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Reading: Locke’s Knowledge of Ideas: Propositional or By Acquaintance?


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Locke’s Knowledge of Ideas: Propositional or By Acquaintance?


Shelley Weinberg

University of Illinois at Urbana-Champaign, US
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Locke seems to have conflicting commitments: we know individual ideas and all knowledge is propositional. This paper shows the conflict to be only apparent. Looking at Locke’s philosophy of language in relation to the Port Royal logic, I argue, first, that Locke allows that we have non-ideational mental content that is signified only at the linguistic level. Second, I argue that this non-ideational content plays a role in what we know when we know an idea. As a result, we can see our knowledge of an idea as a form of knowledge by acquaintance: there is a direct epistemic relation between a mental object (an individual idea) and a knowing subject. But owing to Locke’s logic, that knowledge has a tacit propositional structure expressing the truth of the idea, which gains full signification only linguistically.
How to Cite: Weinberg, S., 2021. Locke’s Knowledge of Ideas: Propositional or By Acquaintance?. Journal of Modern Philosophy, 3(1), p.4. DOI:
  Published on 16 Sep 2021
 Accepted on 06 Apr 2021            Submitted on 03 Jun 2020

1. The Problem

Locke defines knowledge as ‘the perception of the connexion and agreement, or disagreement and repugnancy of any of our Ideas’ (IV.i.2).1 Those agreements come in four categories: identity, necessary co-existence in the same substance, relation in general, and real existence (IV.i.3). Although when push comes to shove Locke thinks that all four categories of agreements are relations, he tells us that some agreements are so ‘peculiar … that they deserve well to be considered under distinct heads, and not under Relation in general, since they are such different grounds of affirmation and negation’ (IV.i.7). That is, Locke could have said that to know an agreement of ideas is simply to know a relation of ideas and left it at that. But then what I take to be a meaningful ‘peculiarity … of the different grounds of affirmation and negation’ would have been glossed over. Locke mentions identity and necessary co-existence in the same substance as having this peculiarity. In this paper, I will confine myself to a discussion of the agreement of identity.

Although very little has been said about what Locke could mean by knowing the identity of an idea and how we know it, some controversy exists in the literature. Of those considering the issue, some think the knowledge is trivial; the agreement is simply the relation between two tokens of an idea type.2 Others argue that Locke means the identity of an idea to be a non-trivial form of knowledge, but they disagree as to what the agreement could be.3 That it is non-trivial would be more in line with Locke’s own view that our intuitive knowledge of the identity of an idea (or knowing an idea) is ‘foundational’ to the rest of knowledge while identity propositions composed of two tokens of an idea type are ‘trifling’ and entirely ‘un-instructive.’4

Others who see knowledge of an idea as non-trivial and foundational argue that Locke’s use of the term ‘know’ indicates room for a distinction between a kind of knowledge by acquaintance (objectual knowledge) and propositional knowledge.5 Our knowledge of an idea would be of the former sort—immediate and non-propositional. Where this interpretation hangs its hat is on a particular reading of this passage:

Everyone that has any Knowledge at all, has, as the Foundation of it, various and distinct Ideas: and it is the first Act of the Mind, (without which, it can never be capable of any Knowledge), to know every one of its Ideas by it self, and distinguish it from others. (IV.vii.4)

The phrase in parentheses would be emphasized: our knowledge (by acquaintance) of an idea is necessary for having any other (propositional) knowledge. On its face, I think this is a plausible reading of the passage, and it would be nice not to have to chalk it up to sloppiness on Locke’s part in this use of the term ‘know.’ Here are a few reasons, though, to think that it’s not quite so simple. First, it seems textually clear and the scholarship is fairly well agreed that Locke thinks all knowledge is propositional, and propositions are compositional in nature.6 In Mr. Locke’s second Reply to the Bishop Of Worcester (Locke 1823: vol. iv, 357), Locke says, ‘Everything which we either know or believe, is some proposition.’ And at the end of Book II after having laid out the ‘origin …, sorts, and extent of our Ideas’ Locke states, ‘it is impossible to speak clearly and distinctly of our Knowledge, which all consists in Propositions, without considering, first, the Nature, Use, and Signification of Language’ (II.xxxiii.19). Thus, he writes Book III.

Second, after defining knowledge as the ‘the perception of the connexion and agreement, or disagreement and repugnancy of any of our Ideas,’ he says, ‘In this alone it consists’ (IV.i.2). That is, any form of knowledge must meet this definition. I take an agreement or disagreement of ideas to be propositional. Third, only a few lines later Locke further clarifies the different forms that knowledge (as an agreement or disagreement of ideas) takes or ‘consists in’: ‘to understand a little more distinctly wherein this agreement or disagreement consists, I think we may reduce it all to these four sorts: 1. Identity, or Diversity; 2. Relation; 3. Co-existence, or necessary connexion; 4. Real Existence’ (IV.i.3). Again, I think it is hard to deny that Locke thinks that knowing the identity of an idea conforms to the definition of knowledge as the perception of an agreement, as propositional. Third, he continues, immediately thereafter, to describe our knowledge of the identity of an idea:

First, As to the first sort of Agreement or Disagreement, viz. Identity, or Diversity. ’Tis the first Act of the Mind, when it has any Sentiments or Ideas at all, to perceive its Ideas, and so far as it perceives them, to know each what it is, and that one is not another. This is so absolutely necessary, that without it there could be no Knowledge, no Reasoning, no Imagination, no distinct Thoughts at all. (IV.i.4)

This is a clear statement that knowing the identity of an idea, a foundational form of knowledge, conforms to the definition of knowledge as the perception of an agreement. Given these passages, and what they seem to imply, I think the knowledge by acquaintance view as normally understood can’t get the job entirely done, for it would fly in the face of Locke’s claims that our knowledge of an idea adheres to the definition of knowledge.

What we have, then, is that knowing an idea, for Locke, is a non-trivial, foundational form of knowledge that is consistent with his propositional definition of knowledge as the perception of an agreement. Yet, I think Locke has a significant hurdle to clear in giving a coherent account. For he seems also to claim that we have knowledge of individual ideas. Locke begins his discussion of our knowledge of the identity of an idea with passages telling us that it is the ‘first Act of the Mind,’ when it has any ideas produced there at all, ‘to know each what it is, and thereby … that one [idea] is not another’ (IV.i.4; see also, e.g., IV.i.2, IV.i.4). Moreover, Locke classifies our knowledge of the identity of an idea as intuitive knowledge, describing it this way: ‘For in this [kind of knowledge], the Mind is at no pains of proving or examining, but perceives the Truth, as the Eye doth light, only by being directed toward it’ (IV.ii.1). He adds, ‘For a Man cannot conceive himself capable of a greater certainty, than to know that any Idea, in his Mind is such, as he perceives it to be …’ (IV.ii.1). Two things are noticeable from just these passages. One, as already mentioned, is that we have knowledge of individual ideas. The other is that knowing an idea is an immediate form of knowledge, both temporally and logically. This next passage seems to confirm the claim:

Everyone that has any Knowledge at all, has, as the Foundation of it, various and distinct Ideas: and it is the first Act of the Mind, (without which, it can never be capable of any Knowledge,) to know every one of its Ideas by it self, and distinguish it from others. Every one finds in himself, that he knows the Ideas he has; That he knows also, when any one is in his Understanding, and what it is; And that when more than one are there, he knows them distinctly and unconfusedly one from another. (IV.vii.4)

So, according to this first claim, we know an individual idea when it is produced in the mind, and we know it just in virtue of perceiving, or having, that idea in the mind.7 Therefore, Locke seems to have inconsistent commitments: we know individual ideas as soon as they appear in the mind and all knowledge is propositional.

I will argue that Locke is not in as bad shape as might first appear. I will argue, first, that Locke, following the Port-Royal logic, allows that some components of mental propositions are not signified by ideas. Thus, there can be non-ideational mental content present in the perception of a single idea. I will also argue, second, that we can understand Locke as having an acquaintance view of sorts—a form of objectual knowledge—but due to the complexity of perceptions of ideas and the role of that non-ideational mental content, it can be seen as consistent with his claim that all knowledge is propositional. I will argue that when we perceive an idea, there is an immediate and direct epistemic relation between the mind (consciousness) and an individual idea (a mental object). Yet I will also argue that Locke, following the Port-Royal logic, understands knowing the idea as including an affirmation of the truth of the idea—as having propositional structure.8 Such an account, I will argue, is philosophically and contextually plausible, and it will reconcile Locke’s seemingly inconsistent claims: that knowledge is propositional and that we have knowledge of individual ideas.

Before moving on, let me address an anxiety. One might think I have engaged in some sleight of hand in appealing to the definition of knowledge as an agreement of ideas (what many read as ‘between ideas’) to support that knowledge of an idea has propositional structure and then to claim that that structure includes a direct epistemic relation between a conscious mind and a single idea. To alleviate that worry, let me put my cards on the table. First, for Locke, all thinking is conscious—even self-conscious—and as I and a good bit of the literature sees it, consciousness is not identical to ordinary perception.9 Second, I have argued elsewhere that for Locke, perceptions of ideas are complex mental states that include more than the act of perception and the idea perceived. In the perception of every idea there is at the very least an idea of existence, and as Locke states also an idea of unity:

Existence and Unity, are two other Ideas, that are suggested to the Understanding, by every Object without, and every Idea within. When Ideas are in our Minds, we consider them as being actually there, as well as we consider things to be actually without us; which is, that they exist, or have Existence: And whatever we can consider as one thing, whether a real Being, or Idea, suggests to the Understanding, the Idea of Unity. (II.vii.7)

Therefore, there are more constituents in the perception of a single idea than the act of perception and the idea perceived; at the very least there is also self-consciousness, an idea of existence, and an idea of unity. So, in the perception of an idea those constituents can form agreements, and if they do, then the perception of a single idea can contain ideational agreements that are expressed propositionally. That is, perceptions of ideas are complex propositional states (Weinberg 2016a).

Another way to think about this is to take a page from Ruth Mattern’s playbook. In reconciling Locke’s general definition of knowledge as the perception of an agreement of ideas with his puzzling definition of sensitive knowledge as an ‘actual real Existence agreeing to any Idea’ (IV.i.7), Mattern argues that Locke failed to sharply separate two different senses of ‘agreement and disagreement of ideas.’ There is the ‘agreement and disagreement within propositions.’ And there is the ‘agreement and disagreement that render propositions true’ (1978: 693, my emphasis). In the latter case, as we have in sensitive knowledge, she argues that what grounds the knowledge is not the relation between the ideas themselves as found in the proposition. Rather, what grounds the knowledge is what guarantees the truth of the proposition. As Mattern explains, these are cases in which there are ‘states of affairs that render propositions true and false …. It is what Locke … terms the “grounds of Affirmation and Negation” (E IV.i.7: 527).’ But in the former case, which Mattern (1978: 693) calls ‘idea-theoretic’ truths, ‘the two sorts of agreements coincide; the relation between ideas is both the state rendering the proposition true and the state of the proposition expressing this truth.’ With this argument in hand, we can see the knowledge of an idea as an ‘idea-theoretic’ truth: our knowledge is grounded in the state of affairs that renders the proposition true (the various constituents making up the complexity of the perception), but at the same time it is also the agreement expressed in the structure or composition of the proposition itself. Given the complexity of the perception of any idea, that structure is due both to an agreement between ideas and between a knowing subject and an idea. (I will have more to say about the nature of the complexity in section 4.) With this in our pocket let’s return to the main argument.

2. The First Case for Non-Ideational Mental Content

That Locke has no room for non-ideational mental content is, no doubt, the orthodox view. Nevertheless, in the very last chapter of the Essay, “Of the Division of the Sciences,” I think Locke states quite clearly that he does. Here he describes three branches of knowledge, the third of which is semiotics, or the ‘Doctrine of Signs,’ which is ‘the ways and means, whereby the Knowledge of both the one and the other [sciences] are attained and communicated’ (IV.xxi.1).10 About the ‘doctrine of signs,’ his logic, Locke says this:

[T]he Doctrine of Signs, the most usual whereof being Words, it is aptly enough termed also … Logick; the business whereof, is to consider the Nature of Signs, the Mind makes use of for the understanding of Things, or conveying its Knowledge to others. For since the Things, the Mind contemplates, are none of them, besides it self, present to the Understanding, ’tis necessary that something else, as a Sign or Representation of the thing it considers, should be present to it: And these are Ideas. And because the Scene of Ideas that makes one Man’s Thoughts, cannot be laid open to the immediate view of another, not laid up any where but in Memory, a no very sure Repository: Therefore to communicate our Thoughts to one another, as well as record them for our own use, Signs of our Ideas are also necessary. (IV.xxi.4)

Locke seems to be committed to a theory of what we might call ‘semantic ascent’: ideas serve as signs of the things they represent (initially either external objects perceived in sensation or mental operations perceived in reflection). That is, words signify ideas, which represent things—external objects or mental activities. Thus, signification proceeds stepwise up the ladder from ideas to words.11 Propositions at the level of ideas, Locke calls ‘mental propositions.’ At the next level of signification, ‘verbal propositions,’ ideas are signified by words (IV.v.3). So, on the orthodox understanding, the constituents of any proposition would be initially ideas and then words.

But notice, in the II.xxi.4 passage, how clearly Locke states that there is one thing we know directly, without needing a sign: the mind itself. He says, ‘For since the Things, the Mind contemplates, are none of them, besides it self, present to the Understanding, ’tis necessary that something else, as a Sign or Representation of the thing it considers, should be present to it: And these are Ideas.’ The mind makes use of ideas to understand everything ‘besides it self.’ Udo Thiel (2011: 115–17) suggests that we see the relation between the mind and itself (its immediate presence to itself) as more of a subject-subject relation as opposed to a subject-object relation. I can be immediately conscious of my own mental acts and myself without having to have ideas of them (see also Weinberg 2016a: 39–40). And once we see that the mind is immediately known to itself without ideational signification, other passages can be read as consistent with that view.

For example, consider Locke’s discussion of signs and their role in proposition formation in his account of truth. Truth, Locke says, is ‘the joining or separating of Signs, as the Things signified by them, do agree or disagree one with another’ (IV.v.2) and ‘Truth properly belongs only to Propositions’ (IV.v.2). Locke is also clear that when we have knowledge we perceive a true proposition. Thus, knowledge would be the perception of a true mental proposition wherein the component signs are ideas. A linguistic expression of that knowledge would be a verbal proposition wherein the component signs are words. But then consider this passage in which Locke is speaking of the truth of an idea:

Though in compliance with the ordinary way of Speaking, I have shewed in what sense, and upon what ground our Ideas may be sometimes called true, or false; yet if we look a little nearer into the matter in all cases, where any Idea is call’d true, or false, it is from some Judgment that the Mind makes, or is supposed to make, that is true, or false. For Truth, or Falshood, being never without some Affirmation, or Negation, Express, or Tacit, it is not to be found, but where signs are joined or separated, according to the agreement, or disagreement, of the Things they stand for. The signs we chiefly use, are either Ideas, or Words, wherewith we make either mental, or verbal Propositions. (II.xxxii.19)

Although it is normally the case that the constituents of mental propositions are ideas and the constituents of verbal propositions are words, in the last line, Locke seems to be saying, not that the signs we use are always ideas and words, but only ‘chiefly’ do we find ideas or words. In addition, he is speaking about the truth of ideas, namely the mental proposition that would precede the verbal proposition expressing our knowledge of the identity of an idea. Although this is far from a proof text, and even though this is a passage about signs, I take Locke’s use of ‘chiefly’ to indicate that constituents of mental propositions can in some cases be non-ideational.12

Yet another passage that can be seen as supporting that Locke is open to non-ideational mental content is his claim that we are aware of our mental operations prior to having ideas of reflection.

And we see the Reason, why ’tis pretty late, before most Children get Ideas of the Operations of their own Minds; and some have not any clear, or perfect Ideas of the greatest part of them all their Lives. Because, though, they pass there continually; yet like floating Visions, they make not deep Impressions enough, to leave in the Mind clear and distinct lasting Ideas, till the Understanding turns inwards upon it self, reflects on its own Operations, and makes them the Object of its own Contemplation. (II.i.8)

Even though young children do not have ideas of reflection, they are aware of the ‘continually passing’ mental operations involved in having ideas of sensation. For example, they would be vaguely aware that they are sensing. It takes another distinct act of reflection by which the mind contemplates, or takes the mental operation as an object of perception to have an idea of that mental operation. Consider also that Locke defines ‘consciousness’ as ‘the perception of what passes in a man’s own mind,’ and he thinks we are conscious of all that passes in the mind (II.i.19).13 From these passages we can infer that Locke has room for non-ideational mental content of which we are conscious, namely pre-ideational awareness of mental operations.14 In the next section, I will argue that Locke does indeed maintain that there are constituents of some verbal propositions that do not signify ideas. That is, some constituents of mental propositions gain signification only at the level of language. Therefore, some mental propositions have non-ideational content.

3. The Second Case for Non-Ideational Content: Signification by Particles

In order to see how Locke could think that we have knowledge of individual ideas and that that knowledge is somehow propositional, there has to be room for mental content that plays a role in knowledge that is not signified by an idea. To see where Locke leaves that room, we need to take a closer look at Locke’s philosophy of language and especially the function of particles. Although we have seen some textual evidence, we have to make sure that Locke’s main thoughts about signification do not commit him to the view that words can signify only ideas. An early wave of interpreters has thought Locke is so committed.15 For example,

The use of Words, is to be sensible Marks of Ideas; and the Ideas they stand for, are their proper and immediate Signification. (III.ii.1)

Words in their primary or immediate Signification, stand for nothing, but the Ideas in the Mind of him that uses them. (III.ii.2)16

But scholarship following that first wave has agreed that Locke does leave room for words that do not signify ideas, most specifically his claims that ‘particles’ (III.vii) and ‘negative or privative words’ (III.i.4) make up at least two exceptions.17 Even Berkeley understood Locke to have made these exceptions to his general rule that words must stand for ideas (Pearce forthcoming). I think Norman Kretzmann (1968: 180–82) is right when he analyzes the passages above (especially the second one from III.ii.2) to be expressing Locke’s view that words primarily signify ideas, and that ‘primary signification’ is by names, namely nouns and adjectives.18 (Importantly, as we will see later, notably absent from Locke’s Book III account of signification is anything about verbs.)19 Given Locke’s own claim in III.vii that particles do not signify ideas, and the emphasis on ‘primary’ in the III.ii.2 passage above, I think it’s reasonable to follow Kretzmann and the rest of the second wave of interpretation.

What are particles and what do they signify if not ideas? Locke says very little about the function of particles in a language. Nevertheless, he seems to think that particles perform an important and under-examined role. He considers particles, ‘which are not truly, by themselves, the names of any Ideas, … of such constant and indispensible use in Language, and do so much contribute to Men’s well expressing themselves’ (III.vii.2). And he adds, ‘This part of Grammar has been, perhaps, as much neglected, as some others over-diligently cultivated’ (III.vii.3). Indeed, given Locke’s general tendency to verbosity, along with his admission of the importance of the role particles play in language and communication, and his recognition of their neglect, he devotes a surprisingly scant two and a half pages to it. What is more, much of what he does say is by way of providing examples of the different ways in which the word ‘but’ (as a particle) functions in the English language.20

Perhaps as close as we can get to a definition of these parts of speech, in Locke, is this:

For what is meant by them [particles] is commonly as hard to be understood in one, as in another Language. They are all marks of some Action, or Intimation of the Mind; and therefore to understand them rightly, the several views, postures, stands, turns, limitations, and exceptions, and several other thoughts of the Mind, for which we have either none, or very deficient Names, are diligently to be studied. (III.vii.4)

Particles seem to denote acts of the mind, or ways in which the mind engages in thinking about the ideas it has. That’s what I take Locke to mean when he says that to understand how particles function, we would have to study ‘the views, postures, stands, turns, etc.’ of the mind that particles ‘mark or intimate.’21 Moreover, there are some things the mind does for which we don’t have names, and the names we have do not clearly convey the mind’s action. That is, not only does Locke think we fail to have a full understanding of how these parts of speech operate in a language, but also he thinks that we don’t have linguistic marks or intimations of all that the mind does.

In addition to a lack of linguistic items to denote mental actions, we also see in his III.vii.2 explanation of particles that not everything that goes on in the mind is signified by an idea. Some mental acts do not strictly follow the ladder of semantic ascent from non- or pre-ideational content, to ideas, to words in a language; rather, some go right from non-ideational status to language. And when they do make that jump, they are signified by a particle. Therefore, some mental content, ‘action[s] or Intimation[s] of the Mind’ gains signification (by a particle) only at the semantic level of language.

In spite of Locke’s lack of attention, or lack of attention to more than the word ‘but,’ and his lack of more detailed analysis, here is something of interest that he does say about particles:

BESIDES Words, which are the names of Ideas in the Mind, there are a great many others that are made use of, to signify the connexion that the Mind gives to Ideas, or Propositions, one with another. The Mind, in communicating its thought to others, does not only need signs of the Ideas it has then before it, but others also, to shew or intimate some particular action of its own, at that time, relating to those Ideas. This it does several ways; as, Is, and Is not, are the general marks of the Mind, affirming or denying. (III.vii.1)22

Particles are used to express things going on in the mind that are not signified by ideas, but nevertheless must be ‘shew[n] or intimated’ in order for aspects of our thinking to be expressed and communicated to others. Locke describes these as ‘particular action[s] of its [the mind’s] own, at that time, relating to … Ideas.’ Some of those aspects he lists as ‘Connexion, Restriction, Distinction, Opposition, Emphasis, etc.’ (III.vii.2):

To think well, it is not enough, that a Man has Ideas clear and distinct in his Thoughts, nor that he observes the agreement, or disagreement of some of them; but he must think in a train, and observe the dependence of his Thoughts and Reasonings, one upon another: And to express well such methodical and rational Thoughts, he must have words to shew what Connexion, Restriction, Distinction, Opposition, Emphasis, etc. he gives to each respective part of his Discourse. To mistake in any of these, is to puzzle, instead of informing, his Hearer: and therefore it is, that those words, which are not truly, by themselves, the names of any Ideas, are of such constant and indispensible use in Language, and do so much contribute to Men’s well expressing themselves. (III.vii.2)

Unfortunately, Locke doesn’t provide any more explanation of these sorts of mental episodes, even though both ‘connexion’ and ‘distinction’ have quite important roles in Locke’s philosophical psychology and his account of knowledge. Indeed, ‘connexion’ Locke uses as a synonym for ‘agreement’ in his IV.ii.1 definition of knowledge. And another text sees ‘distinction,’ or ‘distinguishing an idea,’ as equivalent to ‘knowing’ it.23 His more general example above (in III.vii.1) is of the mental act of affirmation or denial as shown or intimated by the words ‘Is’ or ‘Is not.’ One way to read this is to say that Locke is taking ‘is’ and ‘is not’ as the general way in which we signify the mind’s affirmation or denial of a particular mental act, say the act of perceiving an agreement or connexion of ideas or the mind’s affirmation or denial of the act of distinguishing a particular idea. But is this the right way to read it?

Since Locke doesn’t give us very much else to go on in his discussion of particles and what they signify, we can get some help by looking to the logic that many think most influenced Locke.24 In Logic or the Art of Thinking, Arnauld and Nicole consider linguistic expressions of mental actions in terms of verbs:

I say that the main function of the verb is to signify affirmation, because we shall see below that it is also used to signify other actions of the soul, such as desiring, requesting, commanding, and so on. But this happens only by changing the inflection and the mood, so in this chapter we will consider the verb only in its principle signification, which is what it has in the indicative. Accordingly, we can say that the verb in itself ought to have no other use than to indicate the connection the mind makes between the two terms of a proposition. Only the verb ‘to be,’ however, called the substantive, retains this simplicity, and only in the third person present, ‘is,’ and on certain occasions. (1996: 79)

In this passage, Arnauld and Nicole are explaining how verbs (‘actions words’) are used to signify ‘actions of the soul.’ The main function of any verb in a sentence in which it appears, state Arnauld and Nicole, is to signify affirmation of an action. Finite verbs25 also have other linguistic functions, such as signifying number, tense, and person (1st, 2nd, 3rd) through inflection; an ending is joined to the indicative form of the verb, which serves to signify the number, tense, or person. (I should note that only the substantive, the verb ‘to be’ in the third personal form ‘is,’ however, signifies an act of affirmation alone as opposed to verbs generally, which principally signify an act of affirming something—some action.) So, when two terms are joined (connected) in a proposition by a verb, there is always also present (either explicitly or implied) an affirmation: for example, X is seeing Y, X is hearing Y, and so on. Arnauld and Nicole explain, ‘Because people are naturally led to abbreviate their expressions, they almost always join other significations to affirmation in the same word’ (1996: 79). For example, we say ‘Peter lives’ instead of ‘Peter is living’ mostly out of convenience. Affirming the living of Peter is signified only implicitly in ‘Peter lives.’ So, all verbs signify affirmation but the signification of the affirming is due to an implicit presence of the indicative, third-personal form of the ‘substantive,’ or the verb ‘to be.’ The point is that the mental act of affirming is not always signified on its own, but often as joined implicitly to another word (the verb).

In explaining how verbs function linguistically, Arnauld and Nicole are showing how all verbs implicitly signify the act of affirmation. Importantly, the affirming constitutive of any verb is signified in terms of its exercise or performance, the act in process, rather than as an object of thinking. Gabriel Nuchelmans (1986: 61) explains it this way:

That Locke’s contemporaries were fully aware of this difference between signification in actu exercito [indirectly] and signification in actu significato [directly] is further confirmed by two remarkable passages in the chapter on the verb (II, 2) that was added to Arnauld and Nicole’s La logique ou l’art de penser (1662) in the fifth edition of 1683. The authors, who regard the copula as the only genuine verb, characterize its principal function as consisting in being a mark of affirmation. The finite verb indicates that the discourse in which it occurs is the discourse of someone who does not only conceive of things, but passes judgment on them as well. It is precisely in this respect that the copula-element in the finite verb differs from such names as affirmans and affirmation. The latter words signify affirmation, but only in so far as an actual operation of affirming has become, by a mental act of reflecting, an object of thought. Consequently, they do not signal that the speaker performs an act of affirming; what they signify is the act as a thing conceived of.26

There are a couple of important points to draw out here. First, Arnauld and Nicole see the copula as the only ‘genuine’ verb. I take this to mean that the copula (as an affirmation that an action is occurring) signifies the occurrence of that action by being joined implicitly or explicitly to the verb signifying that action. So, for example, when I say ‘Peter lives’ I am signifying the affirming of the action (living) by Peter by the implicit joining of the copula (‘is’). As mentioned before, really what I am saying when I say ‘Peter lives’ is ‘Peter is living.’ Essentially, we can take the word ‘living’ to be modifying the copula, that is, the signification of the act of affirming is the primary function of the verb where the descriptive aspect of the verb serves to describe what action is affirmed.

Second, the occurrence of a finite verb in a sentence through the implicit joining of the copula signifies a judgment. As Nuchelmans (1986: 61) says, ‘The finite verb indicates that the discourse in which it occurs is the discourse of someone who does not only conceive of things, but passes judgment on them as well.’ This distinction can be understood as the difference between signifying the occurrence of an action and a later reflective consideration of that action. In the former case, it is the action as performed that is signified, where in the latter case it is the action as considered—considered as an object of thinking—that is signified.27

Would Locke have been following Arnauld and Nicole with respect to these two aspects of signification—that the copula is the only genuine verb, which all other finite verbs modify (as adjectives or adverbs), and that there is a distinction between the signification of the performance of a mental act and a later reflection or consideration of it as an object of thinking?28 I think so.29 The former would explain why Locke omitted any discussion of verbs from his Book III account of language and signification.30 And given that he has no chapter on verbs, it would explain why he singles out ‘Is, and Is not’ as ‘general Marks of the mind, affirming or denying’ in his first paragraph explaining the function of particles. Moreover, the latter (a distinction between a mental operation as an object of thinking and its performance) would explain why Locke is careful to say that we have ideas of mental operations produced only by acts of reflection even though we can be conscious of mental operations prior to being able to reflect (Nuchelmans 1986: 64). Indeed, if we reread the earlier IV.xxi.4 passage about Locke’s logic in this context, we find that distinction between the signification of mental actions insofar as they are performed and insofar as they are considered or made objects of reflection. So, when, Locke says, ‘For since the Things, the Mind contemplates, are none of them, besides it self, present to the Understanding, ’tis necessary that something else, as a Sign or Representation of the thing it considers, should be present to it: And these are Ideas’ (IV.xxi.4, my emphasis in bold), we can see him as claiming that mental operations (the mind itself) are not always signified by ideas. Rather, mental operations, although present (conscious) to the mind, are signified by ideas only when they are ‘considered,’ that is made objects of thought as the result of reflection.31 So, it seems that the performance of an act of affirming a mental operation can be signified in a verbal (linguistic) proposition even if it is not first signified by an idea.32

But if an act of affirming a mental action is not signified by an idea, then how is it communicated? Consistent with the III.vii.1 passage already cited, Locke thinks that some mental acts when performed and expressed are signified only linguistically by a particle and not originally by an idea. To repeat some of that passage, he says, ‘The Mind, in communicating its thought to others, does not only need signs of the Ideas it has then before it, but others also, to shew or intimate some particular action of its own, at that time relating to those Ideas’ (III.vii.7). That would mean, for Locke, that there are non- or pre-ideational components of mental propositions, namely mental actions—the performing of a mental operation—that are not signified by ideas but only gain signification through expression in language. In contrast, the same pre-ideational content, say a mental operation (action) when considered or reflected upon, is signified by an idea of reflection. Therefore, in communicating the performing of a mental action, the idea rung on the ladder of signification is skipped. For example, when I look outside and then say to you ‘I see a cat in the yard’ my mental act of affirming my perceiving a cat in the yard (the affirming the occurrent performance of the act of perceiving) is not signified initially by an idea.33

Such an understanding of the difference between signifying an object of thinking and an act of thinking (or ‘posture of the mind in discoursing’ [III.vii.3]) harks back to the medieval distinction between ‘categorematic’ and ‘syncategorematic’ (or ‘non-categorematic’) signification.34 Nuchelmans (1986: 62–63) explains,

The peculiar mode of signifying that is typical of non-categorematic words has as subject the speaker, the speaker’s mind, or the particular word employed. For the relation itself Locke sometimes uses the general verb ‘to signify’, but also, strikingly often, ‘to show’ and ‘to intimate’. These latter verbs seem to be exactly right for indicating the way in which the speaker—and thus the word he uses—reveals a mental act or state of his own which he currently performs or experiences. By uttering the appropriate mark the speaker discloses to the hearer what he is effectively doing and how he is feeling.35

If Locke is following the Port-Royal logic and a traditional view of the difference between categorematic and syncategorematic signification, then mental actions in their performance are not signified by ideas. That is, when I say, ‘I see a cat’ when looking into the yard the performance of my mental act of seeing (sensing/perceiving)—in the moment of seeing—is not signified by an antecedent idea.36 Therefore, a verbal proposition (a linguistic expression) communicating the performance of a mental act in its performance expresses non-ideational mental content. Thus, the performance of any perceptual act, a mental action, skips the idea rung of the semantic ladder achieving signification non-categorematically at the moment of utterance.37

Is there anything else notable that is signified only at the level of linguistic expression? Arnauld and Nicole explain that there is the same sort of non-categorematic signification of the ‘I’ or the subject of the proposition:

Further, in certain cases they have connected it to the subject of the proposition, so that two words, and even a single word, can form a complete proposition. This is possible with two words, as when I say sum homo [I am a man], because sum signifies not only affirmation, but also includes signification of the pronoun ego [I], which is the subject of the proposition…. A single word can form a proposition, for instance when I say vivo, sedeo [I am living, I am seated]. For these verbs contain in themselves both an affirmation and an attribute, as we have already said. Since they are in the first person they also include the subject: ‘I am living,’ ‘I am seated.’ (1996: 79–80)

So in terms of its essence, the verb is a word that signifies an affirmation. But if we wished to include its primary accidents in the definition of the verb, we could define it as follows: vox significans affirmationem cum designation personae, numeri, et temporis. A word that signifies an affirmation while designating person, number, and tense. (1996: 80–81)

Not only does a verb capture an implicit affirmation, but also through the attribution or inflection (the ‘accidents’) it can express the subject. This tells us that not only is the mental act of affirming the action signified with the finite verb, but also the subject, the ‘I,’ is expressed implicitly in the verb. For Locke, this would mean that neither must the affirmation of a mental action (its performance) nor the self acting be signified by an idea. Rather, the performance of the action and the subject acting (namely the ‘I’ in first-personal experience of a mental action) achieve signification only at the level of language—when expressed or reported in language. Thus, mental actions and the first-personal experience of mentally acting are signified by ideas only when considered from a second-order perspective, namely as objects of reflection. That is, only when I turn inward to reflect on my mental operations or on the first-personal way in which I experience my own thinking, are ideas generated of the mental operation and of myself.

4. Our Knowledge of an Idea

How does the foregoing analysis of the function of verbs and particles in a language help Locke out of his problem? Remember that there seems to be a conflict between Locke’s two commitments with respect to the account of knowing an idea. We have knowledge of an individual idea, whenever and as soon as it first enters the mind, and all knowledge is propositional. I contend that these claims are made consistent once we realize, following the Port-Royal logic, that the occurrent performance of a mental action and the subject acting are not signified by ideas prior to their signification by words. Ideas do the signifying only when mental operations and the self are considered as objects of thinking, when they are the objects of reflection. Therefore, there can be elements of the mental state that is the knowledge of an idea (i.e., the truth-making mental content) that are signified only at the level of language.38

What does this do for us? Well, it opens to the door to a propositional account of knowing a single idea. For all components of the proposition (the truth-making mental content) need not all be ideas. That is, we can see the perception of an individual idea as a complex mental state the elements of which constitute the agreement known in knowing an idea. So, really, for Locke, we can think of perceptions of ideas as complex propositional states. Locke’s II.xxxii.1–2 treatment of the ‘truth’ of an idea describes just this situation. Although, Locke says, ‘Truth and Falshood belong, in Propriety of Speech, only to Propositions; yet Ideas are oftentimes termed true or false (as what Words are there, that are not used with great Latitude, and with some deviation from their strict and proper Significations?)’ And even though Locke admits that ‘Ideas, being nothing but bare Appearances or Perceptions in our Minds, cannot properly and simply in themselves be said to be true or false, no more than a single Name of any thing, can be said to be true or false,’ he does tell us what this other sort of ‘truth’ consists in. All truths are propositional, so there must be more to the truth of an idea than the idea simply in itself.

Indeed, Locke tells us that the truth of an idea is propositional:

Though, I think when Ideas themselves are termed true or false, there is still some secret or tacit Proposition, which is the Foundation of that Denomination: as we shall see, if we examine the particular Occasions, wherein they come to be called true or false. In all which, we shall find some kind of Affirmation, or Negation, which is the Reason of that Denomination. (II.xxxii.1)

He continues,

Indeed, both Ideas and Words, may be said to be true in a metaphysical Sense of the Word Truth; as all other Things, that any way exist, are said to be true; i.e. really to be such as they exist. Though in Things called true, even in that Sense, there is, perhaps, a secret reference to our Ideas, look’d upon as the Standards of that Truth, which amounts to a mental Proposition, though it be usually not taken notice of. (II.xxxii.2)

The truth of an idea consists in a ‘secret or tacit Proposition’ expressing, as Locke says, ‘really to be such as [it] exists,’ namely ‘the idea really is as it exists in the mind.’ Expressing it this way, I suggest, is no different from other locutions Locke uses to express what we know when we have knowledge of an idea. He says, ‘The Idea is as I am perceiving it to be’ (IV.ii.1) or he says, ‘I mean some object in the Mind, and consequently determined, i.e. such as it is there seen and perceived to be’ (1975: 13).

What, then are the components of the tacit proposition known in knowing an idea? Consistent with Locke’s verbal propositions (above) expressing that knowledge, when I know an idea there is an agreement between the idea and my conscious perception of it: it really is as ‘I perceive it to be,’ ‘as I perceive it existing in my mind,’ ‘as it is there seen/perceived and perceived [by me] to be.’ Yet, due the complexity of the perception of the idea, there are other elements (the simple ideas of existence and unity [II.i.7]) contributing to both the structure of the proposition and the truth-making mental content. The agreement, then, is composed of ideational and non-ideational elements internal to the complex mental state, and it is expressed linguistically in the ways just mentioned. That is, there is the idea ‘existing’ or ‘there’ (experienced existentially) in my mind due to an agreement between the idea perceived and the simple idea of existence. That perceived idea—the qualitative patterns or features—also agrees to my conscious perception of it,39 namely to the first-personal way in which the idea appears in my mind—as appearing to me, the subject as I occurrently perceive it, which is a direct epistemic relation between a knowing/conscious subject and an idea (object).40 (In addition, I suggest, due to the simple idea of unity—also a part of the complexity—the idea perceived is considered as, Locke says, ‘one thing’ (II.vii.7.)) We might just as easily say, ‘I know the idea,’ ‘I see the idea,’ or ‘I know that object in my mind,’—both ‘that it is there’ and ‘what it is’ (IV.vii.4)—where, the truth-making mental content and the agreements therein (both between ideas and between non-ideational content and an idea) gets cashed out propositionally in Locke’s logic.

Therefore, our problem is solved, for we can have knowledge of an individual idea that has a propositional structure. Why? For two reasons: First, following the Port-Royal logic, Locke allows that we have non-ideational mental content that achieves signification only at the linguistic level; Second, perceptions of ideas, for Locke, are complex propositional states with agreeing components such that being in that mental state conveys knowledge. We can see knowing an idea to be knowledge of acquaintance: there is a direct epistemic relation between a mental object and a knowing subject. But owing to Locke’s logic, at the level of mental content that knowledge has a tacit propositional structure expressing (or affirming) the truth of the idea, which is revealed explicitly only at the level of language.

5. Conclusion

Locke’s account of knowing an idea includes two seemingly conflicting commitments: we know individual ideas in the very first act of perceiving them and all knowledge is propositional. The key to the solution, following the Port-Royal logic, is Locke’s acceptance of the linguistic function of verbs and particles to signify the performance of mental actions without those actions having first been signified by ideas. Once we see the elements internal to the perception of an idea and that Locke allows non-ideational mental content to do work in that perception, which constitutes our knowledge an idea, we can see how knowing an idea is a complex mental state with a tacit propositional structure. Thus, Locke’s account of knowing an idea can be seen as a kind of propositional knowledge by acquaintance.


1All references to Locke’s Essay concerning Human Understanding (Locke 1975) will be appear in the body of the paper by book.chapter.section number. 

2Gibson (1960), Aaron (1971), Mabbott (1973), and Ayers, (1991) mention knowledge of the agreement of identity but dismiss it as ‘trifling.’ Yolton (1985) and Jolley (1999) don’t mention it at all. 

3For example, focusing on Locke’s statements that ‘it is the first act of the Mind … to know every one of its Ideas by it self’ and ‘he can never be in doubt when any Idea is in his Mind, that it is there, and is the Idea is it,’ Lex Newman (2007: 328n18) suggests two complementary agreements: ‘Suppose a sensation of red is occurring in my mind. To know that that idea is presently occurring – that it is in the present contents of my consciousness – is to perceive an agreement between that idea and my general idea of perception. (To know, in addition, that the occurring sensation is of red is to perceive, in addition, an agreement between that idea of sensation and my general idea of red.)’ But this cannot be Locke’s view, for contrary to Locke’s claim that it is the ‘first act of the Mind’ to know its ideas, it would require that we already have the complex general ideas of perception and of red in order to initially know any simple ideas. Matt Priselac (2017: 91–92) has more recently argued that to know the identity of an idea, a non-trivial foundational form of knowledge, ‘depends on the discerning operation of the mind.’ He continues, ‘We achieve knowledge by discerning one idea within some other complex idea. We know, for example, that gold is yellow by discerning yellow within our idea of gold, identifying it as the idea it is within the complex in which it is already perceived.’ I suggest that Priselac’s explanation falls to the same sort of criticism as does Newman’s. It seems that to know the idea yellow, we must already have a complex idea, say of gold, from which to discern it. Given that Locke thinks that all ideas come into the mind ‘simple and unmixed’ (II.ii.1) and it is the first act of the mind to know its ideas, it seems that we would already know the idea yellow before discerning it as one out of the others that are in the idea gold. 

4I don’t think there is any doubt that Locke thinks so, for identity propositions of the type ‘red is red’ (the idea affirmed of itself) are simply statements of something we already know (the idea). Locke says, ‘First, All purely identical Propositions. These obviously, and at first blush, appear to contain no instruction in them. For when we affirm the same Term of it self, whether it be barely verbal, or whether it contains any clear and real Idea, it shews us nothing, but what we must certainly know before, whether such a Proposition be either made by, or proposed to us’ (IV.viii.2). For evidence that Locke thinks our knowledge of an idea is foundational, see IV.vii.4 (cited in just a moment) and IV.viii.3. 

5Wolterstorff (1996: 14) is the only one I know of who holds what I think to be an explicit form of this view in print. I suspect others may think similarly, even if not explicitly in print. This latter point I owe to Galen Strawson. Historically, John Toland, who claimed his view of knowledge to be taken directly from Locke, thought that knowing an idea was not propositional. I thank Kenny Pearce for this point about Toland. Priselac’s (2017) view that idea agreement is to be understood as idea containment and that Locke sees knowing the identity of an idea as discerning it from other ideas (in note 3 above) might be seen as a sort of knowledge by acquaintance. 

6In addition, in the IV.v.1 definition of truth, Locke is clear that the ‘joining or separating of Signs’ whose agreement or disagreement constitutes truth ‘is what by another name, we call Proposition.’ For some of the more recent secondary literature emphasizing Locke’s understanding of knowledge as propositional, see for example, Mattern (1978), Soles (1985), Owen (1999), Newman, (2004; 2007), Rickless (2008), Allen (2013), Weinberg (2016a; 2016b), and Nagel (2016). 

7See also, ‘For let an Idea be as it will, it can be no other but such as the Mind perceives it to be; and that very perception, sufficiently distinguishes it from all other Ideas, which cannot be other, i.e. different, without being perceived to be so. No Idea therefore can be undistinguishable from another, from which it ought to be different, unless you would have it different from itself’ (II.xxix.5). Contrary to what I am arguing, one might take these passages to be about the mental act of ‘discerning’ or distinguishing an idea (II.xi.1). But that is simply to focus on the other side of the same coin. As Michael Ayers (1991: 98) acknowledges, ‘on Locke’s view the perception of the identity or diversity of ideas reduces to the “discerning” or distinguishing of a single idea or two different ideas.’ He continues, ‘Since we cannot have ideas without distinguishing them, the potentiality for a kind of propositional knowledge is bound up with the very having of ideas.’ In a comparison of Locke with Descartes, Louis Loeb (1981: 54) claims that for both ‘we have intuitive knowledge of propositions about the content of our present sensory states.’ I take Loeb to be saying that perceiving or having an idea is to have a form of propositional knowledge. 

8I should note that I am following Ayers (1991), Owen (2007), and Marušić (2014) in seeing Locke as having a ‘one-act’ view of knowledge and judgment. See Ott (2004) for the contrary view that first we form a proposition, and then we affirm it in a second act. See Jaffro (2018) for the view that Locke has a one-act account of intuitive knowledge and a two-act account of other forms of knowledge and judgment. In this paper, I am limiting my argument to our intuitive knowledge of an individual idea. See Buroker (1996) for the view that Arnauld held a one-act account of judgment. 

9More recently, see Coventry and Kriegel (2008), Lähteenmäki (2008; 2011), Jorgensen (2010), Thiel (2011), LoLordo (2012), Weinberg (2008; 2016a). 

10The ‘one and the other’ two sciences are natural philosophy and practical philosophy. 

11I thank Martha Bolton for pointing out the importance of this to me. I will also have more to say about the IV.xxi.4 passage in section 3. 

12Lex Newman in his commentary on a version of this paper at the 2021 Central Division of the APA and an anonymous referee suggested to me that here Locke could be considering other kinds of signs as, for example, when we write ‘I ♥︎ pizza’ or perhaps gestures or something of that sort. I suppose it could be that Locke is thinking something like this, although, to my knowledge, he doesn’t ever speak of signs that are neither ideas nor words. But he does say clearly in IV.xxi.4 that ideas are not needed to signify the mind’s immediate understanding of itself. I should say that I see the IV.xxi.4 passage as the most important to my interpretation, so even if one is not persuaded to read II.xxxii.19 as I do, I don’t see it as counting against the viability of the overall interpretation. And as I alluded to at the end of section 1, and as I hope to make much clearer in section 4, I see my interpretation as fully consistent with Locke’s statement in II.xxxii.19 that ‘Truth, or Falshood, being never without some Affirmation, or Negation, Express, or Tacit, it is not to be found, but where signs are joined or separated, according to the agreement, or disagreement, of the Things they stand for.’ The truth-making mental content signified in the verbal proposition expressing the perception of an idea is made up of an agreement between signs (ideas) as well as between non-ideational content and an idea. 

13A number of recent interpretations, although differing in details, agree that, for Locke, consciousness is a constituent, or ingredient, of the mental state that is the perception of an idea. See Coventry and Kriegel (2008), Lähteenmäki (2008; 2011), Jorgensen (2010), Thiel (2011), LoLordo (2012), Weinberg (2008; 2016a). 

14Wolterstorff (1996: 14) seems to allow the same when he says, ‘Locke rather often speaks of the mind as being directly acquainted with its own ‘operations’ (for example in II,i,4 and II,I,8); and he doesn’t count the mind’s operations among its ideas.’ This is not, by any means however, an uncontroversial view. One might want to read II.i.8 as making a distinction between ‘clear and distinct’ ideas of reflection and those that are not. The interpretive problem is how to maintain Locke’s empiricist principle that all ideas have their source in sensation and reflection, yet young children are, even if only vaguely, conscious of their mental operations. For example, LoLordo (2012: 112–20) makes a distinction between ‘lasting’ and ‘non-lasting’ ideas of reflection. But then there arises the question what is the relation between consciousness and reflection? For LoLordo, consciousness is identical to reflection, but reflection is a source of ideas only when there is added attention and the idea is lodged in memory: what is produced is a ‘lasting’ idea. This interpretation has two infelicitous consequences. First, it denies Locke a second (higher) order account of reflection. All reflection on this view is relegated to first-order thinking. Second, it disrupts the symmetry between the production of ideas in sensation and the production of ideas in reflection, for sensation is a source of ideas even when there is no added attention (II.ix.4). See Weinberg (2016a) for more extensive arguments along these lines. On the other hand, we could perhaps follow Lähteenmäki (2011: 163–67) who emphasizes that consciousness, even if it is an element or constituent of perception, does not have the nature of an act. It is simply the experience of one’s own thinking. But what is consciousness an experience of? Lähteenmäki answers that we are conscious only of ideas, and when we are conscious of our mental acts it is only indirectly through our ideas of those acts—simple ideas of reflection. Lähteenmäki also makes a distinction between ‘passive involuntary reflection and an active voluntary reflection,’ where the former would account for our awareness that even young children have of their mental operations whenever they are thinking—similar to what LoLordo calls ‘non-lasting ideas.’ I take it that Lähteenmäki wants to say that consciousness provides the experience of the idea, but the source of the idea is involuntary reflection. One might still ask, though, what is the status of the content of consciousness—the experience of the ‘I’ when I am thinking, what it feels like to be sensing as opposed to remembering—given that it is neither an act of perception nor is it identical to the idea produced in involuntary reflection? Elsewhere, Lähteenmäki (2008: 83) calls it ‘a state of being aware, the feeling of what passes in one’s mind.’ I take this to be a contentful mental state. So, it seems that one can still ask what is the status of this mental content? Is it an idea or is it non-ideational? If the former, then consciousness seems to be a source of ideas; if the latter then Lähteenmäki’s view would have to include that not everything in the mind of which we are aware is an idea. 

15Alston (1964: 22–25), Clapp (1967: vol. 4, 496), Bennett (1971: 20), Henze (1971). 

16Here’s another: ‘… Words … come to be made use of by Men, as the Signs of their Ideas’ (III.ii.1); ‘That then which Words are the Marks of, are the Ideas of the Speaker’ (III.ii.2). 

17Include here Land (1974: 8), Landesman (1976: 24, 34), Woozley (1976: 429), Ashworth (1984: 51–52), and Ayers (1991, I: 22). 

18Ayers (1991, I: 22–23) agrees that words (names) standing for subjects and predicates are signifying ideas. 

19See, for example, Kretzmann (1968: 180). Landesman (1976: 24n6) considers that Locke does say in II.xviii.2 that verbs correspond to ideas, namely ideas of modes. For example, Locke has a discussion of the simple idea of motion in III.iv.9, but Landesman admits ‘that the examples Locke selects to discuss in detail are most often common nouns applicable to bodies.’ 

20Here are some examples: ‘BUT, to say no more; I saw BUT two planets; You pray; BUT is it not GOD would bring you to the true Religion, and All animals have sense; BUT a Dog is an Animal’ (III.vii.5). 

21According to Ashworth (1984: 57, 59), such a view has its roots in scholastic logic, which Locke’s Oxford education would have exposed him to. As opposed to categorematic words, or ‘ordinary lexical items,’ which signified concepts, ‘… syncategorematic words, that is logical connectives, quantifiers, adverbs, and so on, signified only “in some way.” They corresponded not to concepts, but to mental acts of affirmation, negation, distribution, or other ways of modifying the things thought about, and it was obvious to medieval and post-medieval logicians that there need be no straightforward correspondence between the number and position of syncategorematic words in a sentence and these mental acts.’ 

22Remember that in IV.xxi.4 Locke states, ‘For since the Things, the Mind contemplates, are none of them, besides itself, present to the Understanding, ’tis necessary that something else, as a Sign or Representation of the thing it considers, should be present to it: And these are Ideas’ (my emphasis in bold). That the mind is present to itself without signification by an idea would be consistent with the claim in this (III.vii.1) passage in which Locke says that particles directly ‘intimate some particular action of its [the mind’s] own’ without the need for an intermediary idea. See also Jaffro (2018: 180): ‘Even though there is an important difference between marks of affirmation and negation (which, as I understand Locke, “signify the connexion that the Mind gives to Ideas”) and particles proper (which “connect not only parts of Propositions but whole Sentences to one another”) affirmation and negation are terms that Locke puts in the same category as particles, according to the logico-grammatical tradition, which assimilates particles, verbs, and copula to syncategorematic terms, markers of operations and not conceptions.’ How particles perform their function and what they actually signify, insofar as they are signifying ‘mental actions of [our] own … relating to Ideas,’ will be explained shortly. 

23Here again is Locke’s IV.i.2 definition of knowledge: Knowledge then seems to me to be nothing but the perception of the connexion and agreement, or disagreement and repugnancy of any of our Ideas. Also, we can see ‘distinction’ as equivalent to knowing an idea in the first act of perceiving it: ‘… the Mind clearly and infallibly perceives each Idea to agree with it self, and to be what it is; … And this is does without any pains, labour, or deduction; but at first view, by its natural power of perception and distinction’ (IV.i.4). I think this is preliminary evidence that Locke’s mention of ‘distinction’ and ‘connexion’ as acts signified by particles has to do with acts of the mind involved in knowledge and specifically knowledge of an idea. See also, again, note 7. 

24Nuchelmans (1985), Ayers (1991), Van der Schaar (2008), Ott (2002), Marušić (2014), Pearce (2017; 2019), Jaffro (2018). 

25A finite verb is one that shows person, tense, and number. Non-finite verbs are generally in the infinitive form and are not inflected; they do not show person, tense, or number. 

26See also Pearce (2016: 377). 

27Ashworth (1984: 52) notes that we find the same distinction in William Ockham’s Summa Logicae (1974: 194–95): ‘As Ockham has pointed out in the fourteenth century, it is one thing to exercise an act of affirming or denying, and quite another thing to speak about that act. Particles indicate that a mental act is being exercised, they do not signify these acts as objects.’ See also Ayers (1991: vol. 1, 204–5) who finds the same similarity (a link between medieval theory and seventeenth century logic) between Locke and John Buridan. 

28John Wilkins (1668: 304), a contemporary in the linguistic tradition of the Royal Society says this: ‘By the word Predicate, I mean likewise all that which follows the Copula in the same sentence, whereof the Adjective (if any such there be) immediately next after the Copula, is commonly incorporated with it in instituted Languages, and both together make up that which Grammarians call a Verb.’ As Land (1974: 3) explains, ‘Verbs may invariably be reduced to the form “adjective + copula” and the copula is an “essential particle”.’ 

29No copy of the 1683 edition of Logic or the Art of Thinking was found in Locke’s library according to the best record we have. But given the amount of evidence offered in the next few pages, it seems reasonable, nonetheless, that at the very least Locke was thinking along the same lines. And given that these ideas can be traced to medieval logicians and contemporaries in the Royal Society (see especially notes 27 and 28), it’s not a far stretch to see Locke thinking similarly. Moreover, as Kenneth Pearce (2019: 89–90) has compellingly argued, Locke’s reasons for writing Book III of the Essay (on language), after having already completed what are now the surviving drafts that do not include it, parallel Arnauld and Nicole’s reasons for adding the chapter on the verb (and other material on language) to the 1683 edition of the Logic. First, there is wide agreement that the original design of the Essay mirrors the structure of the Logic: it moves from an account of the origin and nature of ideas and the distinctions between them, to judgments or propositions, to the nature of reasoning, to a division of the sciences. Second, continues Pearce, in the Logic, ‘the material is added at the very beginning of Part II, on judgments, and is said to be useful for understanding judgments because “The mind is accustomed to linking [words and ideas] so closely that we can scarcely conceive one without the other, so that the idea of the thing, prompts the idea of the sound, and the idea of the sound that of the thing” [Logic 1996: 73–74].’ Locke tells us, similarly, his reasons for adding the material on language in between his treatment of ideas and his account of propositions/judgments and knowledge: ‘There is so close a connection between Ideas and words … that it is impossible to speak clearly and distinctly of our Knowledge, which all consists in propositions, without considering, first, the Nature, Use, and Signification of Language’ (II.xxxiii.19). These similarities are striking. I agree with Pearce that the evidence that Locke was familiar with Arnauld and Nicole’s material on language added to the 1683 edition of the Logic is not conclusive. But also I agree with Pearce that given his arguments, and now with the addition of mine, surely the conclusion is plausible. 

30See also Nuchelmans (1986: 63–64): ‘It seems to me that the fact that Locke does not discuss verbs as such in the third book of the Essay is explained most satisfactorily by the assumption that he follows, among others, the authors of the Port-Royal Grammar and Logic in regarding the copula as the only genuine verb; and, being a syncategorematic mark of the performance of an act of affirming, the copula is not a sign of an idea.’ Kretzmann (1968: 179) agrees that Locke adopts syncategorematic signification ‘ruling out’ that words signify only ideas. With respect to verbs, Kretzmann (1968: 180) explains, ‘Locke does briefly consider the signification of verbs in Book Two and at the beginning of Book Three, but in a way quite detached from the semantic theory developed in Book Three, where verbs are not discussed as such. While he does not explicitly exclude verbs from the scope of his main thesis [that words signify only ideas], he never includes them either; and what he has to say about words in Book Three shows that his governing and perhaps exclusive concern was with nouns and adjectives, or “names.”’ According to Wilkins (1668: 304) too, a verb has no distinct place amongst integrals in a philosophical grammar: ‘By the word Predicate, I mean … all that which follows the Copula in the same sentence, whereof the Adjective (if any such there be) immediately next after the Copula, is commonly incorporated with it in instituted Languages, and both together make up that which Grammarians call the Verb.’ See again also Land (1974). 

31Arnauld (1990): 71) makes the same point in his distinction between ‘implicit’ and ‘explicit’ reflection. The former, which we can also think of as consciousness, is a reflexive aspect of perception, which accompanies all thought. Explicit reflection is a second order act in which one perception is the object of another: ‘[O]ur thought or perception is essentially reflective upon itself: or as it is rather better said in Latin, est sui conscia. For I do not think without knowing that I think; I do not know a square without knowing that I know it … I do not imagine I see the sun, without being certain that I imagine I see it…. [A]s well as this implicit reflection which accompanies all our perceptions, there is also something explicit, which occurs when we examine our perception by means of another perception.’ See Steven Nadler (1989: 118–22). For more current agreement with Nadler on this particular point, see Weinberg (2016a: 14–15), and Pearce (2019: 90–91). I see Locke’s understanding of consciousness as similar to Arnauld’s implicit reflection and to views of La Forge and Lamy, in that there is a one level reflexive aspect to consciousness (Arnauld’s implicit reflection) and a second (higher) order reflection (Arnauld’s explicit reflection). I see Locke as understanding consciousness as a reflexive constituent of every perception. Therefore, consciousness plays an epistemic role. But I do not agree with those who see two different kinds of reflection to make sense of the different ways in which we are aware of mental operations. For those positions see the only difference between implicit and explicit reflection in Locke as a matter of attention—whether or not the perception is attended to, which is contrary to Arnauld’s explicit reflection as a second (higher) order act. (See again note 14.) In addition, that Locke was following the Port-Royal logic—the logic of the day—does not mean he would follow Arnauld in everything else. In thinking about what to call what Arnauld termed ‘reflexion virtuelle’ (implicit reflection), I think it more plausible that Locke looked to Cudworth, who had given the English term ‘consciousness’ philosophical meaning. See also Thiel (1994; 2011). Given the employment of the new term, and Locke’s close relationship to Cudworth, it makes sense that Locke would use the English term ‘consciousness’ instead of reverting to the distinction between mental states as found in French. In thinking about Locke’s relation to Cudworth on consciousness, I am most sympathetic to Pécharman (2014). 

32As Nuchelmans duly notes: Interpretations arguing that particles must be signifying ideas (see note 15) fail to notice this distinction and so mistakenly claim that mental acts even in their performance would be signified by an idea of reflection. Clapp (1967: vol. 4, 496) says this: ‘Again a difficulty arises. If “is” and “is not” stand for the mind’s act of affirming or denying, then either the mind directly apprehends its own actions in some way or we do have ideas of affirmation or denial. If we do have ideas of the mind’s acts, then these words ought to signify the ideas of these acts; if we do not have ideas which these words signify, then either we do not apprehend them or something else besides ideas is the object of the mind when it thinks.’ See also Bennett (1971: 20). But, as just cited, there is textual evidence that the mind does apprehend itself directly and indirectly via ideas of reflection (IV.xxi.4). 

33See Landesman (1976: 34): ‘Particles signify the mind’s own actions in bringing its ideas together into bits of connected thinking (III.vii.1, III.vii.6). Locke’s remarks about the copula suggest what he has in mind: “Is and is not are the general marks of the mind, affirming, or denying (3.7.1)” … In general, because the same “names” can occur in different speech acts, a further linguistic mechanism is required to indicate which is the intended act.’ 

34See again notes 21 and 27. 

35Again here is Nuchelmans (1986: 64): ‘Particles, then, in so far as they are actually used, are marks of some action, posture, or feeling exemplified by the speaker’s mind at the moment of utterance…. Someone who wants to describe, classify, and explain their use and force in language must enter into his own thoughts and observe nicely the several actions and postures of his mind in discoursing. From the second-order vantage point taken by philosophers and grammarians, the performed acts and felt states of which particles are marks when actually used, are contemplated and examined through acts of reflecting and thus become objects of thought and ideas of reflection. As such, of course, they can no longer be expressed by particles; the appropriate linguistic tools by which they are mentioned and denoted as things conceived of are those words which are names of ideas in the mind.’ 

36Bennett (2001: vol. 2, 116–17) attributes this view to Locke, but then argues that Locke should have also employed this aspect of his theory of meaning to understanding what ‘thing’ as substance apart from its properties denotes. Citing III.vii.1, 4, Bennett says, ‘His theory of meaning has, as we have seen, two parts: one for general classificatory terms, the other for words like ‘if’ and ‘but’ and ‘is’, which he calls ‘particles’. The latter, he says, do not stand for ideas but rather express mental operations on ideas.’ That Bennett extends the use of particles to other mental operations (actions) is evident in his explanation of how Locke should have explained the meaning of ‘thing’: ‘When I say ‘This is an orange’ I mean that there are here instances of certain properties such as orangeness, sphericalness, etc., and I indicate that I am operating on my ideas of those instances in a certain combining manner. This, though crude and only partial, is better than the obviously doomed attempt to associate ‘thing’ with a type of idea.’ 

37In order to avoid any confusion, Locke does say, in II.xxi.72, ‘what is signified by Verbs that Grammarians call Active, does not always signify Action; v.g. this Proposition: I see the Moon, or a Star, or I feel the heat of the Sun, though expressed by a Verb Active, does not signify any Action in me, whereby I operate on those Substances; but only the reception of the Ideas of light, roundness, and heat, wherein I am not active, but barely passive, and cannot, in that position of my Eyes or Body, avoid receiving them.’ Here Locke is distinguishing active and passive powers, not making a claim that in sensing we are not engaging in a mental operation or act of perceiving. 

38Wolterstorff (1996: 21) admits that ‘Locke’s actual view, as distinguished from his official view, was that facts available to one for one’s “perception” have not only one’s own ideas as their constituents but also one’s mental acts, and perhaps oneself.’ See also Weinberg (2016a: 69) and for more recent views that perceptions of ideas, for Locke, have an internal complexity. 

39See also II.xxxii.26: ‘Upon the whole matter, I think, That our Ideas, as they are considered by the Mind, either in reference to the proper signification of their Names; or in reference to the reality of Things, may very fitly be called right, or wrong Ideas, according as they agree, or disagree to those Patterns to which they are referred. But if any one had rather call them true, or false, ’tis fit he use a liberty which every one has, to call Things by those Names he thinks best; though in propriety of Speech, Truth, or Falshood, will, I think, scarce agree to them, but as they, some way or other, virtually contain in them some mental Proposition.’ Here Locke confirms that when ideas are true there is ‘contained in them some mental Proposition’ ‘according as they agree … to those Patterns to which they are referred.’ 

40One might here object that there is more than one act of predication captured in each of these verbal propositions: 1) there is a connecting of the I and the occurrent mental act of perceiving signified by ‘I perceiving’ or ‘I am perceiving,’ and 2) there is the connecting of the idea perceived and the I perceiving it signified by the verbal proposition, ‘The idea is as I am perceiving it to be.’ I think that is right, but unproblematic. Much of Locke’s philosophical psychology (what goes on in the mind when we engage in different kinds of thinking) is much more complicated than the simple way in which it is presented in the Essay. To give just one example, consider all that’s involved in the mental act of naming an idea. As Land (1974: 14) explains, ‘The name thus becomes a thing of some complexity in Locke’s philosophy. The name “table” involves not only the idea of a table, the physical sign table, and the idea of the sign table, but also the act connecting or assigning that idea to the idea of a table and the memory idea of that act of assignment. The successful understanding of a name is the product of all these elements duly assembled.’ Notice that along with all the different ideas in the mind in grasping the meaning of ‘table’ there is also an act of connecting the idea to the name. Even the act of signification itself, for Locke, seems to be propositional. Indeed, along with the two agreements I have outlined in the perception of an idea, there would also be an agreement between the ‘I perceiving’ and the simple idea of existence, which makes full sense of Locke’s IV.ix.3 claim about the intuitive knowledge of our own existence: ‘In every Act of Sensation, Reasoning, or Thinking, we are conscious to our selves of our own Being; and, in this Matter, come not short of the highest degree of Certainty.’ In the perception of any idea, we also know that we exist. 


I want to thank Martha Bolton whose critical comments on my book spurred me to think more carefully about the issue, and especially Kenny Pearce, for his generosity in conversations and comments on earlier versions of this paper. I would also like to thank the Chicago Modern Philosophy Roundtable (2017), NJ/NYC Early Modern Group (2018), Princeton Early Modern Conference in Philosophy of Mind (2018), audiences at Indiana University (2018), the University of Massachusetts Amherst (2019) and particularly Joseph Levine, the St. Louis Seminar in Early Modern Philosophy (2019), my commentator Lex Newman and the audience at the Central Division Meeting of the APA (2021), and the anonymous referees for this journal.

Competing Interests

The author has no competing interests to declare.


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