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Reading: Incompatibilism and the Principle of Sufficient Reason in Kant’s Nova Dilucidatio


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Incompatibilism and the Principle of Sufficient Reason in Kant’s Nova Dilucidatio


Aaron Wells

University of Paderborn, DE
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The consensus is that in his 1755 Nova Dilucidatio, Kant endorsed broadly Leibnizian compatibilism, then switched to a strongly incompatibilist position in the early 1760s. I argue for an alternative, incompatibilist reading of the Nova Dilucidatio. On this reading, actions are partly grounded in indeterministic acts of volition, and partly in prior conative or cognitive motivations. Actions resulting from volitions are determined by volitions, but volitions themselves are not fully determined. This move, which was standard in medieval treatments of free choice, explains why Kant is so critical of Crusius’s version of libertarian freedom: Kant understands Crusius as making actions entirely random. In defense of this reading, I offer a new analysis of the version of the principle of sufficient reason that appears in the Nova Dilucidatio. This principle can be read as merely guaranteeing grounds for the existence of things or substances, rather than efficient causes for states and events. As such, the principle need not exclude libertarian freedom. Along the way, I seek to illuminate obscure aspects of Kant’s 1755 views on moral psychology, action theory, and the threat of theological determinism.

How to Cite: Wells, A., 2022. Incompatibilism and the Principle of Sufficient Reason in Kant’s Nova Dilucidatio. Journal of Modern Philosophy, 4(1), p.3. DOI:
  Published on 31 Jan 2022
 Accepted on 13 Sep 2021            Submitted on 16 Oct 2020

Nearly all commentators agree that Kant endorses agent-causal compatibilism in his 1755 Nova Dilucidatio, his first publication to deal in detail with metaphysical issues.1 Kant’s position is usually taken as Leibnizian. On such a reading, freedom would not be compatible with the determination of our actions by external natural things and their laws, but is nevertheless compatible with deterministic laws that are as it were built into the nature of each agent from creation.

In this paper, I argue that Kant is in fact committed to an incompatibilist position in 1755. But some preparatory work will be needed. In section 1, I start by distinguishing between what I’ll call source spontaneity and a more radical indeterministic spontaneity, which involves genuine alternative possibilities in action. While Kant does defend a kind of source spontaneity in the Nova Dilucidatio, his metaphysics rules out the strong version of this doctrine affirmed by Leibniz. For Kant, any finite agent is causally affected by other finite beings, and not just (as for Leibniz) by God and itself.

I then argue in section 2 that Kant’s occasional failures to distinguish these two kinds of spontaneity should not blind us to passages stating that metaphysical spontaneity is required for freedom. On my reading, Kant endorses worries about determinism, which threatens to make us mere machines, pushing moral responsibility for our actions back to God and undermining both kinds of spontaneity. Kant rejects Leibnizian appeals to merely hypothetical determination, and repeatedly commits himself to a libertarian account of freedom as involving indeterministic acts of volition and a capacity to do otherwise. While there are some passages that seem at first glance to express a contrary, compatibilist view, I’ll argue that they are far less conclusive than is usually assumed.

I grant, however, that Kant critiques radical strands of libertarianism which would make our actions random or lacking in any reason. These criticisms of a position Kant attributes to Crusius are usually taken to establish that the Dilucidatio does not endorse libertarian freedom. Like many medieval thinkers, Kant does not take randomness and complete causal determination to be exclusive options: acts of volition, though indeterministic, are not entirely groundless but partly grounded in prior conative or cognitive motivations.

In section 3, I further support this reading by responding to a particularly pressing objection. The Nova Dilucidatio defends a version of the principle of sufficient reason. And the principle of sufficient reason is often thought to entail determinism or even necessitarianism. No room seems left for an incompatibilist reading. I suggest, however, that Kant’s principle can be read as importantly restricted. On this reading, the existence of contingent things (res), rather than their states or modes, is what requires a ground or reason. This reading can help with some of the open interpretive questions about the nature and scope of Kant’s 1755 principle of sufficient reason. I conclude, in section 4, by stressing how in 1755 Kant is already committed to a conception of freedom that involves responsiveness to law; this is a well-known cornerstone of his later practical philosophy.

1. Two Kinds of Spontaneity

In the Nova Dilucidatio (henceforth ‘ND’), Kant repeatedly asserts that willing freely requires acting spontaneously (ND 1:400, 1:402). A natural way to read these claims is as committing Kant to an incompatibilist position. Indeed, Martin Schönfeld (2000: 157) concludes from these passages that Kant takes volition to be an act of ‘spontaneous causation’ that cannot be fully determined by ‘deterministic chains of antecedent grounds.’ In the end I will agree with Schönfeld’s conclusion. Jeremy Byrd (2008: 77 n. 19) points out, however, that Kant’s referring to the will as ‘spontaneous’ here is not in itself enough to establish this conclusion.

To see why, we need to take a brief look at Leibniz. Many of his texts seem to lay out a compatibilist account of freedom.2 A key necessary condition for our liberté, as Leibniz puts it in the Theodicy, is ‘spontanéité, with which we determine ourselves’ (1875–90: VI, III §288). But spontaneity in this sense need not involve independence from deterministic, antecedent grounds. Rather, Leibniz is stressing that we are the source of our actions, even if these actions were fully antecedently determined at creation. So long as ‘God alone’ externally determines us, Leibniz contends in §32 of the “Discourse on Metaphysics,” we enjoy ‘perfect spontaneity’ (1989: 64).

Kant was familiar with the Theodicy and thus, presumably, with these ideas. Some of his earliest surviving notes (Reflexionen 3703–5), which I return to below, discuss Leibniz and Pope in the context of a 1755 prize-essay competition on optimism. Kant also knew Baumgarten’s Metaphysics, which defines spontaneous actions as those depending on causal grounds ‘inside the agent’ (2013: §704). More generally, as Karl Ameriks (1991) notes, throughout Kant’s career the term spontaneity can stand for various kinds of freedom, some much stronger than others. In the current context, then, we cannot assume that spontaneity means anything more than being the source of one’s actions in some sense or other. I will call this source spontaneity, in contrast with indeterministic spontaneity. The latter involves genuine alternative possible volitions that are not predetermined; source spontaneity by contrast makes no claims about predetermination.

Kant certainly insists on the importance of source spontaneity, and more generally of determining ‘whence’ a certain consequence ‘is necessary’: that is, what determines the consequence to be one way rather than otherwise (ND 1:400). Plausibly, for Kant in the ND, a necessary condition for my acting freely is that my actions are not merely imposed on me from the outside; I must (in part) be their source.

Kant also seems to follow Leibniz in distinguishing between various faculties that may motivate action. Free action is linked to motivations based in the interplay between our will and intellectual faculties. These motivations are cognitive rather than fully determined by conative impulses and sensations. By contrast, nonhuman animals act solely on impulses and sensations (NE 1:400–401; compare Theodicy III §288). But commitment to this source criterion for free action does not exclude endorsing further necessary conditions on freedom, such as indeterministic spontaneity. Similarly, even if the involvement of a certain cognitive kind of motivation is a necessary condition for freedom, there are further crucial questions about the role of the will in action.

In the remainder of this section, before turning to the question of whether Kant is committed to indeterministic spontaneity, I want to explore why his version of source spontaneity must be significantly weaker than the one endorsed by Leibniz.

To ensure that ‘God alone’ externally determines us, Leibniz denies that created substances causally interact. This safeguards a strong form of source spontaneity in the face of metaphysical threats. Leibniz may thereby avoid at least some of an incompatibilist’s worries about determinism. One such worry is the way in which determinism often entails that agents are determined by value-neutral external causes and principles (Adams 1994: 21; Jorati 2017: 115). Leibniz thinks he can avoid this worry, because in his system we are only determined by our own teleological nature and by God, who chose to create the best possible world. In response, Martin Knutzen (1745) and other eighteenth-century readers worried that Leibniz’s doctrine of mind-body parallelism entails that our mental activities are non-causally determined, because they must agree with whatever our bodies in fact do.

Whatever one makes of Leibniz’s defense of compatibilism, it is clear that Kant cannot accept core tenets of Leibnizian metaphysics in the ND, insofar as he accepts causal interaction among created things. Kant’s earliest publication on Living Forces—mostly written in the mid-1740s—affirms that the soul physically interacts with bodies and is subject to dynamical laws (1:20–21). While Kant’s works in the 1750s and 60s raise complications for this picture, he continues to regard humans as embodied, worldly beings.3 Unlike Leibniz, he insists on direct efficient-causal connections between created substances (ND 1:410–12). I’ll eventually return to some details of this argument, but it is worth stressing that by Kant’s lights this interactionist picture is supposed to follow from rationalist first principles. That is, a consistent Leibnizian rationalist ought to embrace causal interaction, or so Kant argues (Laywine 1993: 25–42; Langton 1998: 104–9).

But that means giving up on the demanding source spontaneity Leibniz attributed to finite substances. Kant’s early source spontaneity thus seems to be a matter of degree: free actions are not sufficiently or totally determined by external influences. They never seem to be entirely free of such influences, for as further discussed in section 3, external causal interaction with other created beings looks like a necessary condition for free action. This is a pretty commonsensical position: benevolence, for example, plausibly requires other finite agents to interact with. But it is not a position Leibniz could accept.

Unlike Leibniz, then, Kant leaves finite substances subject to value-neutral external causes and principles that need not have any direct connection to purposiveness or teleology. Our actions may originate, for example, in contingent patterns of Humean custom with external grounds, or the attractive and repulsive forces of matter.

To be sure, the early Kant takes nature to be teleological in some respects. But token natural causes may be value-neutral. Prompted by the Lisbon disaster, Kant writes in 1756 that earthquakes are

planted in nature by God as a proper consequence of fixed laws. [a human being] has no right … to expect only pleasant consequences from the laws of nature that God has ordained. (1:431; cf. 2:104–5)

While such ‘fixed laws’ may be wisely chosen and hence not globally value-neutral, Kant warns against seeing the local consequences of these laws—even destructive earthquakes—as providentially chosen. Instead, the earthquake must be regarded as a mere by-product of laws of nature that were established for other ends. Considered in itself, the earthquake is value-neutral, even if its effects are not. This means that if the early Kant is to be read as a compatibilist, he cannot be seen as pursuing an important Leibnizian strategy to soften the consequences of determinism.

To sum up, Kant did not adopt the metaphysics and teleology Leibniz used to back up a strong source conception of spontaneity. In fact, Kant’s early metaphysical and theological commitments rule out his endorsing a compatibilist conception of freedom that Leibniz would recognize as adequate. This does not establish Kant’s incompatibilism; but it at least shows that in 1755 Kant was not a Leibnizian compatibilist.

2. Freedom of the Will in the Nova Dilucidatio

I now lay out several lines of textual evidence that the ND is committed to an incompatibilist position, and also address texts that are usually taken to support a compatibilist reading. Let me begin with a brief overview.

One main source of evidence I present is Kant’s discussion of how agents must relate to the created world—and ultimately to a creative God—if their freedom is to be preserved. I argue in section 2.1 that, in relatively neglected passages, Kant worries that strict determinism will undermine freedom, and denies that Leibniz’s invocation of hypothetical necessity offers a way out. In other words, he is not just metaphysically committed to a view of freedom that differs from Leibnizian compatibilism (as we saw in section 1), but explicitly rejects key tenets of Leibniz’s doctrine on freedom and determinism.

Here Byrd recommends we see the ND as endorsing strict necessitarianism. Now, Kant accepts the entailment that if God created the actual world necessarily, the ‘immutable necessity of all things’ would follow (ND 1:399). As we will see, however, the textual evidence strongly suggests that Kant rejects necessitarianism. He denies that God created the actual world necessarily.

The question remains whether in the case of finite agency, Kant endorsed determinism in the created world plus some non-Leibnizian compatibilist position. Against this, I’ll argue in section 2.2 that the ND takes seriously objections from Crusius and others that determinism undermines the freedom of finite agents. These objections apply to a wide range of compatibilist positions, Leibnizian or not. Invoking source spontaneity does not answer them. Kant’s acceptance of these objections means that it is most charitable to read his conception of freedom as involving not just source spontaneity but indeterministic spontaneity as well.

Still, interpreters are nearly unanimous that when the ND turns to freedom of the will and moral psychology, it defends compatibilism against Crusius’s incompatibilism. Section 2.2 provides three main kinds of response to this consensus. First, I lay out a reading on which Kant’s focus is rejecting a radical form of libertarianism he associates with Crusius. Therefore, Kant’s objections need not generalize to all incompatibilist positions. Second, I present direct textual evidence that in a number of passages concerning freedom of the will and moral psychology, Kant commits himself to an incompatibilist position. Third, I discuss various passages that appear to endorse compatibilism, and argue that they are not as conclusive as might be assumed.

Even if this textual case is not completely decisive, the aforementioned considerations of charity favor an incompatibilist reading. On my reading, the ND can be read as offering astute criticisms both of compatibilism and of a certain mistaken conception of what is involved in libertarian freedom. Standard readings, by contrast, must see Kant as insisting on some type of compatibilism in a work that also sets out a battery of unrefuted objections to compatibilism.

It is another question whether in 1755 Kant fully faces up to his indeterministic commitments. Perhaps not. But he would hardly be alone in this among seventeenth- and eighteenth-century philosophers (cf. Sleigh, Chappell, and Della Rocca 1998). Moreover, one would be equally justified in worrying that in his confirmed libertarian writings of the early 1760s, Kant fails to provide an adequate metaphysical account of how indeterministic freedom fits into nature.

In section 3, I hope to alleviate one particular source of anxiety on this point. Incompatibilism, I argue, need not conflict with Kant’s version of the principle of sufficient reason, or with some related metaphysical principles he endorses. The principle can be read as significantly limited in its implications, although it does range over actions ‘possessed of moral freedom’ (ND 1:401). That is, the rationalist project of the ND does not need to be read as conflicting with incompatibilism.

2.1. Creation and freedom

In the Critique of Practical Reason, Kant famously dismisses Leibniz’s conception of freedom as ‘nothing better than the freedom of a turnspit,’ a contraption that in a sense generates effects ‘once it is wound up’; analogously, Leibnizian monads are wound up at creation like bits of spiritual ‘machinery’ (5:97; cf. 28:267). Although a monad is the immediate cause of its own states, it is just as passive as a turnspit with respect to the nature with which it was created. Once this nature is determined, on Kant’s reading, the complete history of the monad is fixed.

Additionally, Leibniz’s system raises the suspicion that God turns out to be the author of human sin, even though Leibniz deployed various strategies to make room for human responsibility, such as a distinction between absolute and hypothetical necessity. One philosopher who pressed this worry was Christian Crusius. He was particularly worried about the role of Leibniz’s version of the principle of sufficient reason.4 As we’ll see, Kant engages with Crusius on this topic in detail in the ND.

The standard reading of Kant’s early career, summarized by Christopher Insole, is that up until around 1763 he remained ‘content’ with a compatibilism ‘whereby we are determined by the chain of determining grounds that rests ultimately in God’ (2013: 67). If the turnspit worry occurred to Kant at all during this period, on this reading, it did not trouble him (Insole 2013: 74).

Little attention has been paid to the fact that already in the ND, Kant raises versions of both the turnspit and authorship worries about Leibniz’s conception of freedom, and takes these worries to be interconnected. Additionally, he denies that Leibniz can resolve these problems with the absolute–hypothetical necessity distinction. Regarding the worry that God is the author of sin, Kant writes:

If, as happens in the case of machines, intelligent beings were able to comport themselves passively in relation to those things which impel them towards certain determinations and changes, I should not deny that the blame for all things could be shifted to God as the Architect of the machine. But those things which happen through the will of beings endowed with understanding and the spontaneous power itself of self-determination obviously issue from an inner principle, from conscious desires and from a choice of one of the alternatives according to the freedom of the power of choice. (ND 1:404)

Here Kant connects a worry about God’s authorship of sin to the idea that being the source of one’s actions does not rule out being a merely passive ‘machine.’ That is, if finite agents were merely causally passive in the face of a prior series of grounds, ‘blame’ really would be shifted to the ‘Architect of the machine.’ This indicates that Kant’s references to ‘inner’ causal powers in the second half of the quotation are meant to contrast not just with the causal powers of other created beings, but with God as creating the world and all of the agents in it. It is noteworthy that in the mid-1760s, when Kant is widely agreed to endorse a libertarian conception of freedom, he uses the same language. Freedom is contrasted with being ‘passive’ in relation to ‘a highest productive cause’ such as God, as well as with respect to created ‘objects’ that ‘affect’ us (Refl 3856 17:314).

Returning to the 1755 text, Kant goes on to link moral imputability to acting on an ‘inner principle of self-determination’ (ND 1:405). In context, the relevant principles would need to be independent of God’s choice to create agents with particular natures: therefore, it would apparently need to rest on something like a power to do otherwise.

He also asks why an omnipotent God ‘permitted’ sin rather than preventing it, and provides an answer that reveals his thinking about freedom (ND 1:404). Permitting sin is not the same as causing it, and Kant contends that God can only prevent sin by ‘warnings, threats, encouragements, and furnishing the means,’ because only these indirect divine actions could be ‘compatible with human freedom’ (ND 1:404–5). These limitations on divine action suggest a conception of human freedom that allows for alternative possibilities. God permits sin because the only alternative would involve suppressing human freedom. Contrast a Leibnizian account. If God creates agents such that they necessarily will sin, these agents would be free, for a Leibnizian, because they act with source spontaneity.

This reading is reinforced by notes dating from a year or two before the publication of the ND. Kant is considering questions of theodicy: specifically, why a perfectly good God would allow for moral evils.

Freely acting beings might have avoided many evil actions, and they would have greatly pleased God had they done so. However, the choice of the lesser of two evils, of which one was the lack of freedom and the other of the morally best, was an unavoidable necessity. … Gratitude is due to the Eternal Wisdom for having admitted only the smallest amount of evil. (Refl. 3304 17:232)

Note the counterfactual language in the first sentence, which suggests an incompatibilist account of freedom. In actuality, freely acting beings have committed many evil actions, but they might have done otherwise. As the next sentences make clear, Kant’s view is that God allows freely committed moral evil because it is a better alternative than eliminating creaturely freedom in order to make beings that always acted morally perfectly. Absolutely speaking, God could prevent moral evil, but chooses not to do so because this would impinge on creaturely freedom. There is no suggestion that hypothetical morally perfect beings would lack the source spontaneity required by a Leibnizian account of freedom. Since creatures’ freedom would ex hypothesi be undermined in this scenario, freedom must consist in something more than mere source spontaneity.

Kant further distances himself from Leibnizian compatibilism by denying that the absolute or logical contingency of our actions can help here, so long as these actions are still taken to be hypothetically necessary.5 The fact that it was in God’s absolute power to have chosen to create a different world is cold comfort for us if it is still really impossible, given the world that God actually created, for us to do otherwise (ND 1:399). For then, it is not in our power to have done otherwise, holding the rest of the created world fixed. With these criticisms, Kant may well be observing a standard medieval distinction between real modality and what was often called logical modality. This distinction was taken as a way of specifying more precisely what freedom of decision requires, rather than as ruling it out.6

Kant’s rejection of these Leibnizian strategies has been noted by Byrd (2008: 73), who concludes, however, that Kant endorses necessitarianism. Necessitarianism indeed threatens if one (i) reads Kant as a Leibnizian compatibilist about divine and creaturely action; (ii) takes seriously his rejection of Leibnizian ways of avoiding a slide into necessitarianism; and (iii) observes that he does not articulate alternative strategies for avoiding necessitarianism.

I favor avoiding a necessitarian reading by denying (i). But some passages in the ND do lend apparent support to Byrd’s necessitarian reading, and need to be discussed. Kant holds that divine actions are morally necessitated. He goes on to state that moral necessity has no less ‘force or … effective power’ than absolute necessity; therefore, in particular, ‘the act of creation is not indeterminate in God, but … is so certainly determinate that the opposite would be unworthy of God’ (ND 1:400).

A look at the context of this striking passage, however, indicates the crucial role of semantic and epistemological assumptions about the certainty of a truth or proposition (ND 1:400). The key doctrines Kant wants to defend here are the ‘certainty’ of divine foreknowledge, as well as our ‘certainty’ about God’s choice to create (1:400). The ‘force’ or ‘power’ of moral necessity can be read as concerning the certainty, for some agents, of truths or propositions.

It might be objected that if God is certain about a truth, then that truth will be necessary. But the assumption made behind this objection cannot be taken for granted in Kant’s historical context. It was routinely denied by late Scholastics in the context of debates over divine foreknowledge, and was even denied by Leibniz in his bid to distinguish his position on creation from necessitarianism (Murray 2004: 18–19, 27 n. 53). That is, it was common to think that the certainty of divine foreknowledge does not entail the necessity of the objects of divine foreknowledge. This would be true a fortiori for whatever certainties finite beings like us are capable of. Kant’s own view is that creatures’ free actions are ‘determined by their own grounds’ and not by divine foreknowledge. If foreknowledge necessitated our actions then source spontaneity, as well as indeterministic spontaneity, would be ruled out (ND 1:405). So Kant’s remarks do not entail that on his view, moral necessity collapses into absolute metaphysical necessity.

Note too that this passage does not literally claim that failing to create is beyond God’s power. The claim it makes is normative: such an act would be unworthy of God’s perfect goodness. This sort of merely deontic interpretation of moral necessity can be found in Samuel Clarke, and sometimes in Leibniz. On this understanding, as Robert Adams has put it, ‘the morally necessary is what one morally ought to do,’ and does not eliminate the possibility of acting otherwise (Adams 1994: 22). The late Scholastics had developed more metaphysically loaded conceptions of moral necessity. But these too, as Michael Murray (1995; 2004) has discussed, were meant to avoid standard causal and metaphysical determination, though without making action brute or unintelligible.7 In sum, while moral necessity was conceived in a number of ways in Kant’s time, and it is debatable just how Kant understood it, a point of consensus was that moral necessity does not amount to strict or absolute necessity.8

A wider look at Kant’s writings in the 1750s provides further evidence against a necessitarian reading. Kant’s definition of the principle of sufficient reason as ranging only over contingent properties is incompatible with necessitarianism (ND 1:396). Kant’s central argument for this principle relies on there being some contingent properties. At least some of God’s properties, by contrast, are necessary. These are not subject to the principle of sufficient reason. So Kant clearly admits a distinction between the necessary and the contingent. This is important for the thesis, better known from Kant’s Only Possible Argument but already in place in 1755, that the material content of possibilia has its ‘source’ or ground in God (ND 1:396). Kant denies, however, that what is grounded in God in this way is ‘absolutely necessary’ (1:396). I take him to mean that what actually happens is contingent, even though God grounds the material content of all possibilities.

Again and again during this period, Kant refers to divine choice in creation, understood in terms of possibly doing otherwise. We’ve already seen Kant consider the possibility of God’s creating morally perfect but unfree agents. Elsewhere he writes that God could have chosen to perfect our intellects, or to restore decaying planetary orbits to a more perfect state (ND 1:408). Presumably such choices, though absolutely within God’s power, would have resulted in an overall worse world, and thus are morally impossible.

In the contemporaneous Universal Natural History, many passages are straightforwardly committed to alternative divine choices in creation (UNH 1:271, 1:311, 1:336, 1:345). The work also lays out a distinction between God’s free choices and consequences of these choices that are not free. For example, God’s creating various features of celestial bodies was ‘tied to the mechanical rules of motion’ and therefore not an ‘act [of] free choice’ (1:344).9 Even these unfree creative acts have their source in God. Here too, then, it appears that divine freedom of choice must be distinguished in terms of something beyond mere source spontaneity.

In sum, Kant takes seriously the possibility that divine creation could undermine our freedom. He rejects the Leibnizian response to this problem, without capitulating to necessitarianism. Instead, many of his discussions suggest that (a) God enjoys freedom of alternative possibilities in creation, thus that there is at least one agent with indeterministic spontaneity; and (b) God could have undermined our freedom or spontaneity by creating us differently, even though in such a scenario we would still be the sources of our actions.

2.2. Activity, determination, and the will

Let us turn to Kant’s account of free action. We’ve seen that it includes, as a necessary condition, some degree of source spontaneity. The motivations of free action are recognizably mine, originating for example in my understanding, and not merely in ‘external stimuli and impulses’ (ND 1:400).

But this does not settle how the will’s choices relate to motivation. Three main options are available. First, the will’s choices might be strictly determined by prior motivations—whether these are appetites or desires, or else based in the understanding and other theoretical faculties. Versions of this determinist position have been attributed, rightly or wrongly, to Aquinas, Hobbes, Gassendi, and Wolff.10 Intellectual or psychological determinism threatens to exclude indeterministic spontaneity by making volitions effects that, though not necessarily physical, are broadly natural. Furthermore, once non-volitional motivations are taken as sufficient conditions for action, one can ask about the sufficient conditions for these motivations themselves. If this series of sufficient conditions leads beyond the agent, source spontaneity also seems to be in jeopardy.

Second, voluntary choice might be entirely unconstrained by motivations, such that ‘actions are the product of chance’ (ND 1:402). This is the view Kant attributes to Crusius, perhaps based on the Crusian idea that it is in virtue of their existence that things are spatiotemporally determinate and located outside of thought. More precisely, as Kant reads Crusius, the sheer actuality or existence of a particular event ‘alone’ explains why this event, and no other possible event, occurs: ‘there is no need for a determining ground’ beyond the existence of token acts of ‘the free will’ (ND 1:397). The underlying idea seems to be that an event is necessary at the time that it takes place, insofar as in occurring, it excludes other possibilities. This was a common medieval view, already endorsed by Boethius in his Consolation and commentary on De Interpretatione. It was supposed to be consistent with regarding the future as open or contingent (Normore 2003; Pasnau 2020).

Kant’s characterization of Crusius’s position—leaving aside its accuracy—makes it hard to see how an act of free will could have any explanation stemming from the agent.11 On Kant’s understanding, the appeal to the actuality of an event in the present is supposed to dodge questions about how past events or ‘grounds which are prior’ in time relate to the actual existence of a given action (ND 1:397). In this Crusian account, a present event or act is posited as self-explanatory. Its actual existence somehow explains what it is. But ‘such actions,’ Kant objects, ‘would scarcely deserve to figure among the prerogatives of intelligent beings’ (1:400). These actions are random or inexplicable, for they have no explanation in terms of volitional or motivational grounds. Kant’s Crusius is committed to actions that occur without any determination by prior ‘reason,’ ‘deliberation,’ or ‘motives’ (1:406).

Third, one could adopt a middle position, on which choice is partly but not fully grounded in prior motivations such as reasons and desires. Decisions would then not be fully predetermined. They would have substantive grounds, because they are partly grounded in a free act of willing. Not all would accept the coherence of this middle position, and I will not try to defend it here. But views of this kind are of major historical significance. As Thomas Pink (2004) has argued, this was the standard Latin medieval conception of free will, from Aquinas up until Hobbes. The basic idea is that voluntary action, as an exercise of the will, is neither the mere effect of motivational forces such as appetites and desires, nor of rational beliefs about what should be done.

Many medieval accounts, for instance from Scotus and Suárez, add that a voluntary action in accordance with a reason is metaphysically distinctive, and cannot be understood on the model of a mere effect in the material world. Matter and its natural powers were typically seen as more determined, less free, than volitions (Pink 2004: 131). To take Scotus’s example, the natural power of coldness qua coldness cannot warm, whereas the will can either perform a given act or its opposite (1997: 137–39). Note that on this sort of picture, examining the sources of an action may provide a reliable criterion for determining whether it is free. Free actions will not find their source merely in the powers of matter. But this is because the relevant sources are not fully determined, and not just because they are internal to the agent.

I will argue that many passages in the ND commit Kant to this sort of middle position. We can begin by considering his initial line of response to the Crusian position on freedom. This response is surprisingly concessive. Kant grants to Crusius that if an agent’s ‘act of free will’ actually ‘exists’ at a certain time, then this would exclude the agent’s doing the opposite at that time (ND 1:397).

Here we would expect a determinist to stress that this act of free will is also fully determined by temporally prior grounds. Instead, Kant agrees with the Crusian that the act of free will is ‘contingent’ (ND 1:397). The main point he stresses is rather that the ‘inner existence’ of the act of free will—I take this to mean something like its intrinsic properties—does not entail all the relations that this act stands in (1:397). In particular, the intrinsic properties of the act do not entail all of the act’s temporal properties, such as the time it began.12 So these temporal properties are not determined by the mere existence of the act of free will, but by some external grounds. He takes this to be enough to refute Crusius’s position. The key conclusion here, though, is only that the act of free will has at least one prior determining ground (because its temporal, relational properties have at least one prior determining ground). This does not settle whether the ‘inner’ or essential properties of the act are so determined.

More broadly, Kant repeatedly considers a strictly deterministic picture of the universe in order to address the Crusian objection that the principle of sufficient reason is unacceptable because it entails determinism. Kant grants that determinism poses a serious threat to freedom (1:399, 1:403).13 One of his main lines of response to the Crusian objection is to repeatedly deny that free actions, whether exercised by God or by finite agents, result from ‘ineluctable necessity’ (ND 1:400). Given the context, which is a discussion of determinism, Kant is plausibly read as saying that free actions are incompatible not only with necessitarianism, but also with determinism.

Next, we can turn to more positive accounts of free willing in the ND. Kant is careful to distinguish ‘desire[s]’ and ‘reasons’—i.e., the conative and the cognitive—from our voluntary ‘striv[ing] … in conformity with’ desires or reasons (ND 1:403). The way Kant deploys this distinction appears to commit him to incompatibilist conclusions. For example, he explicitly distinguishes ‘necessitated’ actions, such as reflexes, from free actions that are merely ‘called forth’ by motives (ND 1:400). To be sure, a distinction between the sources of free action is in play here: a necessary condition for my action’s being free is its (partial) source in my rational will. But I take Kant to also be articulating a difference in the (in)determinacy of action. The distinction between being necessitated and being merely called forth concerns not the source, but the metaphysical status of action.14

Furthermore, in a somewhat neglected passage, Kant characterizes free action as involving the ‘spontaneous inclination of the will,’ stressing that ‘the power to perform an action is suspended in a state of indifference relative to each of the two directions in which it could realize itself’ (ND 1:401). Kant singles out the will, rather than mere ‘motives of the understanding,’ as the locus of spontaneity in free action (ND 1:401). Since acts of will are just as internal to an agent as are motives of understanding, the distinction he is drawing does not seem to concern source spontaneity.

Here Kant uses indeterministic, counterfactual language: at least in one stage of choosing, volition is indifferent between alternatives and ‘could realize itself’ in either of two ways (ND 1:401). In stressing that volition might either perform an act or its opposite (unlike powers that are bound to realize a particular alternative), Kant seems to be calling attention to the undetermined nature of volition, above and beyond the question of the source of action. Kant frames this as a ‘generally admitted’ view or datum that needs to be accounted for in an adequate account of the freedom of rational agents (ND 1:401).

Kant does immediately add some qualifications. Free action does not consist ‘in being carried away in all directions towards objects by some vacillating impulse’ (ND 1:401). But this need not imply anything more than a rejection of the radical liberty of indifference that Kant associates with Crusius. Kant wants to claim that there must be some ‘inner’ motivational ‘grounds’ for action, but this does not entail that the will is strictly determined (ND 1:401). In claiming that free action is not indifferent vacillation, then, Kant is not taking back his commitment to the ‘generally admitted’ view that free willing involves genuine alternative possibilities. So it does not seem that Kant propounds this view merely in order to refute it.15

Kant’s non-Crusian position is elaborated in a dialogue between Caius, who takes actions to be in some sense random and groundless, and Titius, who apparently defends Kant’s position. Titius argues at length that the liberty of indifference is in some sense an ‘illusion’ (ND 1:403). At first glance, this looks like a rejection of incompatibilism. Yet in the history of discussions of free will, the term indifference is often ambiguous (Sleigh, Chappell, and Della Rocca 1998: 1210). While medieval conceptions of indifference typically stressed the metaphysical availability of alternative possibilities, later thinkers such as Descartes took indifferent actions to be those an agent performs for no reason. Such ambiguities also appear in Leibniz. He denies that rational agents ever act without a reason (1875–90: III:168; 1989: 195). Yet immediately after rejecting this sort of ‘equilibre’ or equipoise, Leibniz upholds what he calls ‘liberty of indifference’; so by the latter he cannot mean action without any reason (1875–90: VI:128).

Now when Caius claims that agents are in a radical ‘state of indifference’ between acting one way and another, he grants that this notion of freedom would ‘eliminate’ ‘all … grounds’ of free action whatsoever (ND 1:402). So in taking issue with Caius, Titius need not reject the metaphysics of libertarian freedom as such. Titius can be read as endorsing a conception of rational volition on which voluntary actions are not indifferent, in the sense of being merely random or a matter of chance. The action is grounded in volition and in (non-determining) prior motives. As Kant has Titius say:

Since grounds attract us in a certain direction, we shall, in order at least to test our freedom, turn our attention in the opposite direction, and thus make it preponderant so that the desire is directed thus and not otherwise. In this way, we shall easily persuade ourselves that determining grounds must certainly be present. (ND 1:403, emphasis in original)

The final phrase in this passage stresses the way in which action is determined by grounds. But this is downstream, as it were, from the volitional locus of freedom: we ‘make’ up at least some of these grounds voluntarily.

Elsewhere, Titius objects that Caius’s conception of freedom threatens to remove any role for prior motives, and especially for virtues of character, which Titius seems to understand as pre-existing settled dispositions (1:402). If actions are really performed with freedom of indifference, then they will not be based on virtuous dispositions but on inexplicable ‘baleful fate’ or ‘chance’ (1:402). Titius’s speech is at a high rhetorical pitch. It ridicules Caius’s position as counterintuitive and self-undermining. This style contrasts with Kant’s earlier neutral or positive assessment of the ability to do otherwise as a ‘generally admitted’ datum. So both the content of Titius’s objections and their tone indicate that Kant draws a distinction between the metaphysics of libertarian freedom as such, and a Crusian version of libertarianism that entails indifference.

To illustrate the account of agency that Kant has Titius advocate, consider a case where I am choosing among two desirable but mutually exclusive options. For example, I am planning to have dinner, but decide to go for a walk instead. Titius does not describe this as a case where my antecedent motives strictly determine that I will go for a walk. Instead, the idea is that I will to make the desire to go for a walk ‘preponderant’ over the desire to dine that had previously ‘attract[ed]’ me, and so act in accordance with the former desire (ND 1:403).

My going for a walk is not random or indifferent. Rather, it is ‘determined by grounds.’ It is grounded at least in (1) my desire to go for a walk and (2) my willing to act in accordance with that desire, rather than the desire to have dinner (ND 1:402). Here (2) is an act of agent causation not fully determined by prior motives.

Should this distinction seem overly subtle, it is worth noting that Baumgarten—despite his reticence about the metaphysical issues involved in freedom—also clearly distinguishes two faculties associated with (1) and (2). Baumgarten takes arbitrium as a faculty of ‘desiring and averting’ (that is, a faculty that determines motivations) to be distinct from libertas as a faculty of ‘willing or refusing’ (2013: §712, §719). Kant flags this distinction in notes on Baumgarten from around 1755, classifying sensory appetites as examples of mere arbitrium (Belieben) and indicating that non-human animals as well as humans possess this faculty (Kant 2019: 277, 280). Both of these faculties are in turn distinct, on Baumgarten’s account, from mere spontaneitas in the sense of being the source of one’s actions.

I take the moral psychology of the ND to also invoke (3) a capacity to attend to a given desire rather than some other, conflicting desire. Kant stresses, for example, that ‘turn[ing] our attention’ is an exercise of ‘freedom’ (ND 1:403). This capacity originates in the will: genuine choice involves willing our intellectual faculties to reflectively consider our options before acting. Options can then be made more or less salient.16 Cases of akrasia and other kinds of practical irrationality can be partly explained in terms of this capacity. Through selective attention, the lesser good may seem to be to be a better choice than the greater; one may even come to entirely ignore a good.

These discussions of agency and moral psychology are importantly linked to Crusian anxieties about determinism. Caius worries that if determinism is true, his responsibility for his own ‘misdeeds’ does not fall on him, since his actions are fated from creation (ND 1:401). The worry, as he puts it, is that ‘every inclination of my will has been completely determined by an antecedent ground … right back to the beginning of all things’ (ND 1:402).

One aspect of Titius’s response to this worry is to stress the importance, in the context of moral responsibility, of an ‘inner principle’ as the source of one’s actions (ND 1:402). This has been taken to commit Kant to a compatibilist position. But that does not follow. On the one hand, it is possible to acknowledge that source spontaneity is crucially involved in moral responsibility, for example in practices of praise and blame, without taking it to be sufficient for free action. On the other hand, we’ve seen that Kant’s interactive metaphysics does not permit actions to originate from an absolutely inner principle.

The first response Titius makes to Caius is in fact straightforwardly concerned with determinism as a threat to the alternative possibilities required for freedom. Titius, speaking for Kant, says:

At any given juncture, the series of interconnected grounds furnishes motives for the performance of an action which are equally attractive in both directions: you readily adopted one of them because acting thus rather than otherwise was more pleasurable to you. But you say: it was already determined by the totality of grounds that I should incline in one particular direction. I should, however, like you to consider whether it is not the case that the spontaneous inclination of your will, according to the attractions of the object, is not required if there is to be a complete ground of action. (ND 1:402)

At the moment of choice, on this picture, the agent has available two ‘equally attractive’ sets of motives. But neither set of motives is a sufficient ground of action. Instead, a further ground must be added, which originates in the will and is not determined by either set of motives. This further ground is a necessary condition for acting in one way, and not the other.

So this passage apparently commits Kant to an incompatibilist account of freedom, on which the way we act is not determined by pre-existing motives, but is also necessarily grounded in the inclination of the will one way or the other. No matter how much ‘the state of things prior to … free acts has been determined,’ the ‘hinge’ of action remains ‘voluntary’ (ND 1:404). Again, going for a walk, as an action based on volitions, may be determined: the will plus all other grounds are jointly sufficient conditions for it. But the volitions themselves need not be determined, even if they are influenced by, or partly grounded in, desire for ‘the attractions of the object.’ While possible objects of choice provide the matter for willing, a further necessary condition for settling choice originates in the agent’s will.

Let us turn, finally, to some passages where Kant can seem, contrary to my reading, to endorse determinism and compatibilism. These passages have been taken to rule out the reading of the ND I defend here. But I’ll argue that they are far from conclusive. In one such passage, Kant writes:

In so far as they [sc., the free actions of human beings] are regarded as determinate, their opposites are indeed excluded; they are not, however, excluded by grounds which are posited as existing outside the desires and spontaneous inclinations of the subject, as if the agent were compelled to perform his actions against his will. … On the contrary, it is in the very inclination of his volitions and desires, insofar as that inclination readily yields to the blandishments of his representations, that his actions are determined by a fixed law and in a connection which is most certain but also free. (ND 1:400)

To begin, note that Kant’s topic is the determination of action by the will, not the determination of the will itself. And his framing of the issue is qualified. Free actions are considered ‘insofar as they … are regarded as determinate.’ Taken literally, this implies that actions could also be regarded as indeterminate.

Even the references to a ‘certain’ connection or a ‘fixed law’ at the end of the passage need not entail strict determinism regarding the will. For this claim is in the first instance about action, which is causally downstream of acts of willing. Additionally, we have seen that in Leibniz and his medieval predecessors, a high degree of certainty is compatible with contingency. Finally, it cannot be assumed that a ‘fixed law’ means a deterministic natural law. For example, moral necessitation might be lawlike without being strictly deterministic. I return to this issue in section 4 below.

While the passage from 1:400 aims in part to defend source spontaneity, I take it to suggest that indeterministic spontaneity is required as well. This lends support to my reading. Consider the first sentence of the passage. On the conception of source spontaneity laid out here, free actions are not grounded in what exists ‘outside the desires and spontaneous inclinations of the subject.’ Kant, however, has shown himself to have grasped Crusius’s objection that if strict determinism were true, the ultimate grounds of free actions would lie outside the subject’s will and spontaneous inclinations. A few pages later, he reiterates that moral responsibility requires that agents’ actions ultimately originate in an ‘inner principle of self-determination’: in the agents ‘themselves,’ rather than a causal chain that merely passes through them (ND 1:404). Kant’s interactive metaphysics, if deterministic, would undermine this kind of ultimate origination of free actions in agents. So there is a way to read this passage as holding that if one takes source spontaneity seriously, as ultimate responsibility, one will be led to see that it requires indeterministic spontaneity at some point in an agent’s history.

Another potentially problematic passage appears in the dialogue between Titius and Caius. In one exchange, Titius may seem to accept determinism and hence compatibilism, implying that Kant does so as well. Caius objects that on Titius’s account of moral psychology, the ‘will could not have failed to incline’ towards one action rather than another, and Titius responds that this does not eliminate spontaneity or freedom, if freedom is properly understood (ND 1:402). However, especially read in the context of Titius’s broader goals in the dialogue, this passage need only commit Kant to the idea that some prior motives (which ‘incline’ it to some extent) were predetermined, rather than that volition is strictly predetermined. While Titius does emphasize here that spontaneous action ‘issues from an inner principle,’ this can accord with a reading on which source spontaneity is a necessary but not sufficient condition for freedom (1:402). Here too, Titius can be read as rejecting a specifically Crusian view rather than possible incompatibilist accounts.17

A final important textual reason why the early Kant has been read as compatibilist is his defense of a version of the principle of sufficient reason. The principle, which he prefers to call the Principle of Determining Ground (PDG), might seem to guarantee that every action is causally determined. And there is a long history of conflict between libertarian freedom and explanatory principles such as the principle of sufficient reason. Murray (2004: 8) contends, for example, that this sort of tension can already be found in Aquinas. I will argue in the following section, however, that Kant’s specific version of the principle of sufficient reason does not exclude an incompatibilist reading.

3. Freedom and the Principle of Sufficient Reason

The whole discussion of freedom in the ND is framed as a defense of the PDG against Crusian objections that such principles entail determinism or necessitarianism, and rule out freedom (ND 1:399). Kant wants to say that the PDG and human freedom are consistent; action is not strictly ‘unavoidable’ (inevitabilis), even if once willed it is ‘bound to happen’ (ND 1:399, 1:402). If Kant believes that his PDG entails strict determinism, while endorsing both the PDG and freedom, then it would follow that he is a compatibilist.

There is, however, a way to reconcile all of this with Kant’s incompatibilism. On one plausible reading, Kant does not take his PDG to entail strict causal determinism or to exclude incompatibilist freedom. Earlier modern philosophers used several strategies to articulate this kind of position. A radical approach was taken by Clarke at the beginning of the eighteenth century. He argued that a global principle of sufficient reason is consistent with libertarian freedom, and can even be used to prove that at least one agent exercising such freedom actually exists.18 A more typical strategy tames the principle of sufficient reason by limiting its scope, such that it need not entail consequences such as general determinism (cf. Della Rocca 2021). I think the early Kant can be read as taking this latter approach. Here I can only provide some reasons why this reading is plausible, rather than defending it in full detail.

Let’s take a closer look at the PDG. Although a central goal of the ND is to defend this principle, Kant is not as clear as one might like in answering a number of questions about it, including:

  1. Why is it called a principle of determining rather than sufficient ground?
  2. Does the PDG appeal to an essentially temporal conception of priority?
  3. What are the PDG’s implications for the causal interaction of created substances?
  4. What is the scope of the PDG?

While I cannot fully clear up all these questions, I’ll argue that what Kant does say about these issues need not preclude libertarian freedom.19

(i) Determining or sufficient grounds? Kant explicitly follows Crusius in regarding the term sufficient ground as ambiguous. Like Crusius, he prefers to speak of a principle of determining ground (ND 1:393). Crusius’s terminological shift is motivated by some of the same commitments that make him think the PDG entails strict determinism. Kant’s making the same shift in terminology does not, however, entail that he shares all of Crusius’s commitments.

Crusius’s point was that the rationalist principle endorsed by Leibniz goes beyond the trivial claim that whatever is actually thus-and-so has sufficient grounds for its being thus-and-so. In the first place, the principle also has explanatory significance, allowing us to understand why something is determinately thus and not otherwise (Crusius 2020: 202; 1964–87: §38). So far, this is basically a terminological issue: the contrastive, explanatory significance of the principle was already stressed by Leibniz.20

But Crusius also makes a key modal move in his interpretation of Leibniz’s principle of sufficient reason, which he also reads in terms of determining grounds:

… From every sufficient reason it is necessary that it be understood why that which is opposed to it does not and cannot exist, as long namely as that reason is posited and the configuration of coexisting things does not change. (2020: 202, emphasis added)

That is, if p falls under the principle of determining ground, there is some set of grounds that necessitates that p rather than ¬p obtains. (I leave open what kind of necessity Crusius takes this to be.) If all our actions fall under the principle of determining ground, then it seems they will be necessitated as well. To avoid this consequence, Crusius contends that some of our actions escape the principle of determining ground. Like God’s creative act, they are ‘first actions which are not efficiently produced by any other thing,’ and can freely be ‘undertaken or omitted’ by the agent (Crusius 2020: 214; 1964–87: §§81–83). In other words, our indeterministic spontaneity is incompatible with our actions’ falling under the scope of the principle of determining ground.

Kant need not take strong metaphysical consequences to be built into the notion of determination. Kant’s discussions of determination instead often focus on its conceptual or semantic ramifications. A determining ground is ‘sufficient’ for us to ‘conceive [a] thing in such and such a way, and in no other’ (ND 1:393). That is, the ground is sufficient for us to conceive of some object ϕ as having the property G rather than ¬G. This does not settle the metaphysical question whether ϕ could have been otherwise, for example having the property ¬G. This latter question depends on whether G is an essential property of ϕ, and the PDG is silent on this.

More generally, Kant sometimes stresses that the PDG, as a principle of truths, ensures that all propositions have a determinate truth-value (ND 1:393–94). This point, closely related to the principle of bivalence, may imply that the world is metaphysically determinate, but need not bring along any particular picture about relations among real things.

(ii) Is antecedence temporal? In my reading of the moral psychology of the ND, an act of willing is somehow prior to outer actions such as turning on a faucet. But must temporal priority always be involved in such cases? The same question can be asked about Kant’s talk of antecedent grounds, which is ambiguous between temporal and non-temporal (metaphysical) antecedence.

In general, an antecedently determining ground is one that has metaphysical priority—it is a so-called ‘real’ rather than ideal ground (ND 1:398). This is not always distinguished from a notion of intelligibility, such that if χ grounds ψ, then if χ did not exist ψ ‘would not be intelligible’ (ND 1:392). Neither of these notions of ground need involve temporal priority or precedence.21 Parts can really, but synchronically ground a whole; substances are prior to accidents; logical truths can atemporally render other logical truths intelligible.

Kant’s moral psychology, of course, often treats grounds that indeed are prior in time. For example, he has Titius argue that any plausible account of free action should allow it to be guided by pre-existing dispositions such as ‘virtue’ (ND 1:402). But Kant never states that actions must only have temporally antecedent grounds. Voluntary action is described as not fully determined by temporally ‘prior’ grounds (ND 1:404). So agent causation through the will may be simultaneous with the action that it grounds.

(iii) The PDG and causal interaction. Kant holds that ‘no change can happen to substances except in so far as they are connected with other substances’ (ND 1:410). Kant calls this the Principle of Succession (PS). Kant suggests that the PS somehow derives from the PDG (ND 1:410–11). This would appear to threaten the somewhat deflationary reading of the PDG I lay out in this section. However, Kant’s actual argument for the PS clearly invokes many premises in addition to the PDG, especially concerning the metaphysics of change in substances. Indeed, it is hard to see how the PS could follow solely from any version of the principle sufficient reason, without auxiliary premises.22

It might be objected that the PS, whatever its grounds, independently rules out libertarian freedom. For Kant holds that our minds or souls are not exempt from the PS, except by supernatural divine intervention (ND 1:413). Since it is plausible that willing involves change across time in a substance, it would follow that on a strong reading of the PS, willing is not caused by substances themselves but solely by external substances acting on them. This would undermine source spontaneity, and thus rule out freedom, however things stand with determinism.

Kant should not be read, however, as endorsing such a strong version of the PS. While it may be controversial that Kant endorses indeterministic spontaneity in this work, all interpreters seem to agree that he takes agents to be at least a partial source of their actions, hence in some way responsible for their own change in state.

An alternative reading of the PS can be brought out by considering the dialectical context in which Kant introduces it. The key conclusion Kant wants to establish is that a causally isolated substance, such as a Leibnizian monad, would not undergo change. Since Leibnizians think created substances do undergo change, if Kant can get them to accept the Principle of Succession, the Leibnizians will be pushed to grant causal interaction among created substances (ND 1:412).

But all Kant needs for this polemical goal is to claim that causal interaction is a necessary or enabling condition for internal change in substances. Causal interaction may be a condition for representations of possible actions that constitute the matter of willing, for example. This does not rule out a libertarian conception of the will. The ability to will or nil need not be wholly determined by representations of possible actions, even if it depends on access to some such representations for its actual exercise. In other words, while the faculty of willing is plausibly intrinsic to agents, any particular volition is not a purely intrinsic property of an agent—in the sense of a property an agent would still have if it were lonely, or the sole non-divine occupant of a possible world. Leibniz, by contrast, seems to think each of us would have the same volitions if we were the only actual substance other than God.

(iv) The scope of the PDG. What then is the metaphysical significance of Kant’s PDG? Many early modern philosophers endorse causal principles, along the lines of the claim that all effects have causes. We might then expect Kant’s principle of determining ground to be a causal principle ranging over all effects. But it is not at all obvious that the ND is committed to this. Kant claims that ‘only the existence of contingent things … requires the support of a determining ground’ (ND 1:396).23 Here a thing is a res, not an object in general. A res must not be confused with a thing’s state or mode.

As such, Kant can be read as endorsing, not a causal principle ranging over effects, but a version of the principle of sufficient reason that dates back to the eleventh century—see Avicenna (2005)—and is perhaps best known for driving Aquinas’s Third Way. This Avicennan principle dictates that if a thing is not necessary in itself, there must be some reason why it exists rather than not. The principle is silent on how things stand with modes, states, or accidents. The same distinction reappears in Kant’s first Critique, when he revisits metaphysical disputes about sufficient grounds. There, he takes the question of our freedom to be in effect a question about the grounds of certain states; this is discussed in the Third Antinomy. It is a different matter how our contingent existence as things or substances is grounded (this is treated in the Fourth Antinomy and subsequent criticisms of the cosmological argument).

Support for this reading can be drawn from Kant’s claim that the PDG shows the existence of a divine understanding as ‘common principle’ of the ‘existence’ of finite substances (ND 1:412–13, emphasis added). This is Kant’s so-called Principle of Coexistence: finite substances cannot ground each other’s existence, so some further ground of the existence of all finite substances is required. In this context God is posited as an efficient productive and conserving cause of existence—and as the formal cause of lawlike relations among substances (ND 1:414). Note that Kant does not claim God produces all the states of finite substances. These substances causally interact with one another once they are created. Substances, not God, produce particular states, with the help of laws of nature.

To sum up my reading, then: it is indeed axiomatic for Kant that contingent existents require a ground of their existence. But he need not be read as taking this to entail that all the states of all contingent existents are causally grounded. Must Kant then follow Crusius in permitting ungrounded first actions? That depends on what action means. Inner acts of will, for Kant, involve indeterministic freedom. But many ordinary actions—turning on a faucet, going for a walk—do have fully determining grounds and are hence not Crusian first actions, even if some of the relevant grounds are themselves acts of will.24

It might be objected that it is arbitrary to limit the principle of sufficient reason in this way, and that charity demands reading Kant as embracing a principle that ranges non-arbitrarily over actions as well as the existence of things. While I won’t settle the philosophical charge of arbitrariness here, as a historical matter it was in fact standard for early modern philosophers to limit the scope of the principle of sufficient reason.

We’ve seen that Crusius does exactly this, even if he seems motivated more by a need to preserve morality rather than any properly metaphysical distinction. Some argue that Leibniz too distinguished between reasons and causes, so as to limit the causal implications of his principle of sufficient reason and avoid causal determinism (Sleigh, Chappell, and Della Rocca 1998: 1259–60).25 Still other interpreters have suggested that even the arch-rationalist Spinoza adopts this kind of limitation strategy. For example, Martin Lin (2019: 164–81) argues that Spinoza restricts the principle to existential truths about things or substances; this looks a lot like the Avicennan principle of sufficient reason I’m attributing to Kant. And Yitzhak Melamed (2013: 96–104) takes Spinoza’s principle to apply to efficient but not immanent causation. Whether or not these readings of Leibniz and Spinoza are correct, they indicate that it need not be uncharitable to read a thinker with rationalist inclinations as limiting the scope of the principle of sufficient reason.

A narrow reading of the scope of Kant’s PDG also affords a response to a piece of textual evidence raised by Byrd (2008: 77 n. 19) against any libertarian reading of the ND. According to Byrd, Kant rules out self-causation. Libertarian freedom must involve self-causation. So Kant must rule out libertarian freedom.

In fact, the passage Byrd cites does not rule out self-causation in general—if this is taken, for example, in the immanent sense in which a substance can be the cause of its states or modes. Rather, Kant argues that it would be ‘absurd’ for a finite res to ground or cause ‘its existence’ (ND 1:394). Libertarian freedom does not, however, require that agents literally create themselves. That view of freedom might indeed be ‘absurd’ if attributed to finite agents. Instead, libertarian freedom requires only that agents freely determine some of their states, namely their volitions. As discussed in section 2.2, it need not even be the case that agents as it were create volitions ex nihilo, without drawing on prior representations for material; at least, that does not follow from the mere ability to have chosen otherwise.

Kant’s nuanced position can be obscured, I think, by his series of objections to Crusius. For as we’ve seen, Crusius also limits the scope of the PDG or principle of sufficient reason. And Kant objects to various claims he attributes to Crusius. Yet these objections do not include the idea that Crusius arbitrarily restricts the PDG. Instead, we’ve seen Kant’s main worry is that Crusius makes action product of mere ‘chance’ or randomness, such that the PDG in no way applies to action (ND 1:402).

4. Conclusion

A well-known problem with random or chance action is that it seems to undermine moral responsibility. This is a concern for Kant as well, as we’ve seen from his discussions of Crusius. In concluding, I want to return to one of Kant’s preferred ways of distinguishing rational action from products of chance. He holds that an agent’s ‘freedom’ is ‘greater’ the more they submit ‘to the law’ (ND 1:402). To determine one’s spontaneity in a random or arbitrary way is thus not to act with genuine freedom. These ideas fit well with Kant’s broadly intellectualist theology, where God aims at ‘the greatest possible perfection’ in the created world, in contrast to Crusius’s focus on will and power (ND 1:404; cf. Schneewind 1998: 445–46; Insole 2013).

This looks like a conception of positive freedom under laws, even if it is not articulated in detail and might be consistent with acting on merely natural laws.26 The idea is elaborated a bit further in Kant’s 1763 Only Possible Argument. There, Kant first suggests that all causality follows some laws, a point that is reiterated later, for example in the Groundwork (4:446).

These need not be the standard laws of nature. Kant notes that there may be supernatural or miraculous laws of divine action, as well as ‘laws of freedom’ for finite agents (OPA 2:110–11). Henry Allison (2020: 72) cautions against reading Kant’s mature conceptions of the moral law, autonomy, and pure practical reason back into this passage. While this is a fair point, Kant’s early works can still be read as envisioning an account of positive freedom that is compatible with generally binding laws. To be sure, the status and content of these laws (let alone the justification of libertarian freedom) has not been worked out in detail, as Kant himself grants in the 1764 “Prize Essay” (2:298). But even in 1755, I hope to have shown, Kant was aware of the metaphysical burdens of this conception of freedom, and drew anti-Leibnizian and ultimately incompatibilist conclusions.


1See Finster (1982), Schneewind (1998: 497–500), Longuenesse (2005: 117–42), Byrd (2008), Hogan (2009: 371), Insole (2013: 65–68), and Allison (2020: 12–32, 43–44). Schönfeld (2000: 154ff.) is unusual in arguing that Kant endorses a libertarian position on free will in the Nova Dilucidatio. But as I will discuss, the textual case Schönfeld lays out is not decisive, and he does not address the question of (in)compatibilism in detail. 

2A standard reading of Leibniz as a compatibilist and a determinist, as laid out by Adams (1994), will provide a helpful foil for interpreting the ND. But my main argument does not depend on the correctness of such a reading. 

3On Kant’s early conception of causal interaction and its implications for our psychology broadly speaking, see Ameriks (2000: 25–83), Laywine (1993), and Watkins (2005). In the 1755 Universal Natural History, Kant speculates that various limitations of our cognitive faculties can be traced to our embodiment in passive, resisting matter (1:330; 1:355–57). Kant revisits these themes, but with more caution, in the 1764 “Essay on the Maladies of the Head.” Metaphysics lectures from around this time indicate that Kant now denies that the soul’s interaction with the body is literally dynamical (28:146). 

4See Crusius (2020: 204–6). Crusius is neutral on whether Leibniz must be committed to God’s authoring sin through his will, or whether this must be traced to ‘blind fate’ (i.e., to the necessary nature of things independent of God’s volition) (2020: 204). Either way, Crusius thinks, the consequences for moral imputation are disastrous. 

5For some of Leibniz’s statements of the distinction between absolute and hypothetical necessity, and its role in safeguarding freedom, see a May 1686 draft letter to Arnauld (1989: 69–70), and a letter to Coste of 19 December 1707 (1989: 193–96). 

6Luis de Molina contended in Disputatio 47 of the 1588 Concordia Liberi Arbitrii that logical contingency is compatible with real ‘fatalistic and infallible necessity’ in the actual created order (Molina 1988: 87). Duns Scotus, by contrast, had argued in the thirteenth century that the mere logical possibility of doing otherwise brings with it a real power to do otherwise, while still distinguishing between these kinds of modality. See Lectura I.39 §§50–51 (Scotus 1994: 116–19). 

7Murray notes that Leibniz sometimes speaks of moral necessity in a more than merely deontic sense, while continuing to distinguish it from strict or absolute necessity, as in draft letters to Arnauld (Leibniz 1875–90: II:37–47). Crusius objected to this distinction, and took Leibniz to be committed to necessitarianism (Schneewind 1998: 455). 

8Later, in his 1759 essay on optimism, Kant may commit himself to a metaphysical rather than merely deontic conception of moral necessity, with respect to divine actions. Yet this discussion actually provides further evidence for reading Kant as an incompatibilist during the 1750s. Moral necessitation impairs freedom of the will: ‘not being able to choose other than that which one distinctly and rightly recognizes as the best constitutes … a constraint which limits the will [ein Zwang des Willens], and a necessity which cancels freedom’ (2:34). That is, even the best possible motivations limit the will and cancel freedom if one lacks the ability to do otherwise. The upshot seems to be that because their choices are not morally necessitated, finite agents are more free than God. 

9Duns Scotus and other medieval authors would have called this an exercise of God’s ordained rather than absolute power (1997: 191–94) 

10See Schneewind (1998: 437–38), Sleigh, Chappell, and Della Rocca (1998), and Murray (2004: 7). Aquinas and Wolff would surely deny that their conceptions of practical reasoning really have deterministic consequences. Gassendi and Hobbes might be willing to embrace determinism. 

11One inaccuracy in Kant’s characterization is that Crusius grounds actions in mental powers and prior mental representations, not just in present existence (Crusius 1964–87: §59; 2020: 223; Schneewind 1998: 446–51; Watkins 2005: 82–93). Kant may also not adequately appreciate Crusius’s special, metaphysically thick conception of existence (Crusius 1964–87: §§46–48). Instead, Kant distinguishes between the ‘real’ properties of possibilia and their actual existence (ND 1:396). This prefigures his thesis (explicitly introduced in the early 1760s) that existence is not a real property. Thus he appears to read the Crusian position as one on which actions are not grounded in any real property whatsoever. It is possible that Kant is obliquely responding to Pietist anti-rationalists such as Joachim Lange, and not only to Crusius. Kant’s notes on Baumgarten from around 1755 contain a number of references to Crusius, with a special focus on basic principles (Grundsätze), but Kant also voices doubts about the status of these principles (Kant 2019: 22, 27, 32–33, 291). 

12This is an instance of the early Kant’s rejection of the reducibility of relations to intrinsic properties (Langton 1998: 97–123). 

13The passage at 1:403 might be taken to straightforwardly endorse determinism, rather than as articulating the Crusian objection that the principle of sufficient reason entails determinism. But in dialogical context, this passage summarizes an objection from Caius (standing in for Crusius) that the principle of sufficient reason eliminates freedom and moral responsibility. Kant’s surrogate Titius says that this deterministic picture is the ‘reason’ why ‘you’ (i.e., Caius) take the principle of sufficient reason to undermine freedom and moral responsibility. Kant, however, rejects both this consequence and the deterministic picture that suggests it. 

14Actions that have their source in reasons may also essentially differ in other respects from actions that originate solely in reflexes or physical causes. Source spontaneity and indeterministic spontaneity may be coextensive, even though the former does not entail the latter. 

15I thank an anonymous referee for raising this interpretive possibility. 

16A long line of thinkers stress our (partial) voluntary control over cognitive or intellectual acts that factor into our choices. See Hatfield (2009: 392–402) on Lucretius and Augustine, and Gallagher (1994) on Aquinas. 

17Another possible way of reading this passage as not committing Kant to determinism, which I cannot develop in detail here, would invoke moral necessity. For moral necessitarians, it might be true that given certain assumptions about the agent’s character, the agent could not have failed to incline in a certain direction; but the agent retains a real, not merely logical, possibility of having done otherwise. 

18See Clarke (1998: 54), a text that may have partly inspired the Thesis argument in Kant’s Third Antinomy. 

19Laywine (1993: 33), Schönfeld (2000: 133–34), and Longuenesse (2005: 121–25) all note the obscurity of Kant’s PDG. Perin (2015) considers an important question about the PDG that I cannot get into here, namely whether Kant has any clear argument for the version of principle ranging over extramental things, as opposed to the ‘realm of truths’ (ND 1:396). 

20See Leibniz (2011: 355–56) and §32 of the Monadology (1989: 217). 

21Cf. Aristotle’s Metaphysics Δ.11. 

22Consider too how the principle of sufficient reason has sometimes been thought to entail the elimination of all relations, including causal connections, between substances (Della Rocca 2021: §3). This is incompatible with Kant’s Principle of Succession. 

23While Kant does not explicitly use the term res in this sentence, he does so slightly earlier, in the course of arguing for this claim by reductio (‘Nihil erit, quod ut exsistens determinet, praeter ipsam rei exsistentiam,’ ND 1:396, emphasis added), and in a later restatement of the same claim (‘Verum rem contingentem nunquam, si a ratione antecedenter determinante discesseris, sufficienter determinatam, hinc nec exsistentem esse posse, si libuerit, etiam alio argumento probabo,’ 1:397, emphasis added). 

24The motion of my hand to turn on a faucet, on this view, would not count as a volition. We find a similar thought in medieval thinkers such as Suárez: moving my hand to turn the faucet on may be an action of some kind, but not in the fundamental sense; my will, not my hand, is responsive to reasons (Pink 2004: 131). So both Kant and the medievals might avoid Ryle’s (1949: 54) problem of a regress of volitions. 

25Some passages from Kant’s Critical period suggest a similar view, such as a reference to an ‘intelligible’ determination of action that rests not on the chain of natural causes but ‘on mere grounds of the understanding’ (auf bloßen Gründen des Verstandes) (A545/B573). 

26See Henrich’s (1957) discussion of Kant’s early engagement with Hutcheson; the latter ultimately categorized moral sense as a merely natural law, like the law of gravity. Crusius’s ethics similarly includes a naturalistically conceived moral drive (Gewissentrieb): see Schneewind (1998: 447–48). Kant’s views might also have developed in response to Baumgarten’s distinction between physical and moral laws in the 1760 Elements of First Practical Philosophy (2020: §60). 


Thanks to Karl Ameriks, Katharina Kraus, Sam Newlands, Fred Rush, Phil Sloan, Eric Watkins, and the editors and referees of the Journal of Modern Philosophy. Research for this article was partly supported by the Deutsche Forschungsgemeinschaft (DFG), project number 435124693.

Competing Interests

No competing interests. (Partial funding from the DFG is declared in the Acknowledgements, but does not reasonably create a conflict of interest.)


    For Kant’s translated works, I use the translations of the Cambridge Edition of Kant’s works (Paul Guyer and Allen Wood, eds., 1992–). Citations of Kant are by volume and page of the Academy Edition—except for Kant (2019), which is cited by page number, and for the Critique of Pure Reason, for which I use the standard A/B pagination.

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