In the course of writing up a paper on Locke’s theory of ideas for a volume on The Lockean Mind, it dawned on me that all complex ideas are conventional signs. So in what follows, I’d like to suggest that, while simple ideas are natural signs of their causes, complex ideas, even complex ideas of substances, are conventional signs that depend on linguistic consolidation.

In recent years, work on representation in Locke has reached some sort of consensus. Most scholars agree that simple ideas represent their causes. But it’s not at all clear what complex ideas represent. If substances are not given in experience, what do complex ideas represent? Do they have corresponding objects? Given Locke’s metaphysics, it seems safe to say that there are no apples, dogs, cats, trees or stones in the world, at least not properly speaking. Let’s unpack this a bit: While the ingredients of complex ideas, i.e. simple ideas, represent the qualities (= properties) that cause them, the resulting complex idea might be said to represent its cause insofar as the simple ideas represent their causes. So the complex idea of an apple might be said to be a natural sign of its cause insofar as the simple ideas (of which it consists), say the ideas of round, green, sweet and firm, are natural signs of qualities. Yet, this cannot be the last word, because complex substance ideas seem to have no direct correlate that they represent. Arguably, we cannot say that the things we think of in virtue of complex ideas are given in experience. My idea of an apple is not simply caused by an apple. Rather the complex idea of apple is made up of ideas of qualities, while the apple as a substantial bearer of the perceived qualities is not itself given in experience but presupposed. Looking at the causal explanation of such ideas, we cannot simply invoke extramental qualities. We also need to take into account the tacit mental operations that form the complex idea out of simple ideas (Essay II, xxiii, 1).

What, then, do complex ideas represent? As I have just said, the idea of an apple can of course be analysed into ideas of qualities. But if the apple idea as such is not taken as a sign of the causes (qualities), what does it represent? To answer this question, it is important to note that Locke appeals to an old distinction between two kinds of ideas, archetypes and copies or ektypes. Traditionally, archetypes would be taken to be ideas in the mind of God, where they serve as blueprints of things to be created. Locke doesn’t appeal to divine ideas, but he still makes use of this distinction when discussing adequate and inadequate ideas (see Essay II, xxxi). Arguably, Locke assumes that our mind forms, stores and names such archetypes when we encounter things or invent moral categories. The archetypes are what Locke calls nominal essences in book III. What does this mean? When we have an occurrent idea of an apple, this idea can be seen as a copy of the archetype through which we recognise the thing as an apple. So when we see an apple, we have in fact an idea that matches to some extent the archetype of apples in our mind.

This archetype-copy relation also forms the foundation for Locke’s famous criticism of our assumption that we have cognitive access to real essences of things. According to Locke, we tend to assume that a present idea of an apple matches the real essence of an apple. But this is a mistake, argues Locke. In fact, we refer it to the nominal essence, which is nothing but an abstract idea with a name annexed to it (see Essay III, iii, 15).

An immediate worry arising from this account is that such archetypes would be highly subjective or instable. After all, nominal essences (or archetypes) of substances are formed in our various accidental encounters with things. But if we invoke Locke’s discussion of language, we can see that he meets this worry. Briefly put, the fact that nominal essences are annexed to names means that these essence ideas are socially consolidated. The linguistic community a speaker is part of will sanction some uses and confirm other uses. This way, the abstract ideas are stabilised and even rectifiable in the light of new discoveries. So if I happen to call apples tomatoes, other users will correct and amend my use of the term, and thus make me adapt the conventional nominal essence.

The upshot is that complex ideas of substances (and mixed modes) are conventional signs to some degree. Although complex ideas consist of simple ideas that can be seen as natural signs of their causes, the complex ideas ultimately function as conventional signs for us. What they present to our mind is not solely determined by what causes their ingredients but also by the patterns that are consolidated within a linguistic community. This means that my occurent idea of an apple, while caused by certain qualities, presents to my mind an apple that I can recognise as an instance of what we call apple, because it has to match the socially consolidated criteria of the nominal essence of apple. Were it not for the historically grown categories salient in my speech community, for instance those for certain kinds of fruit, it is possible that my mind would register the recurrent ideas of certain qualities without ever recognising them as pertaining to a certain kind of thing.

Locke makes this point clear when he writes that ideas without names annexed to them would resemble a library with unbound books in which we could access pages without it being determined to which books the pages belong: ‘He that has complex Ideas, without particular names for them, would be in no better Case than a Bookseller, who had in his Ware-house Volumes, that lay there unbound, and without Titles …’ (Essay III, x, 26-27). The point is that the precise ingredients of our complex ideas, the structure and amount of simple ideas belonging to them, are determined by the naming practice in a given speech community. Thus, although the ingredients themselves have a causal origin, the way the ingredients are bound into bundles and used in thinking is a matter of convention.

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* This piece is now kindly featured by Locke Studies 19 (2019).

I’m exaggerating, but only a bit. Earlier this year, Kenny Pearce* wrote a fine post on “Locke’s Experimental Philosophy of Ideas”, highlighting what is often forgotten: that Locke’s Essay ties in with Baconian natural history. He then goes on to argue that we should also see Locke’s account of ideas as part of that project and concludes:

“This line of interpretation has consequences for how we must understand Locke’s account of ideas. If Locke is following this kind of Baconian methodology then, although he does at various points seek to explain various phenomena, his ‘ideas’ cannot be understood as theoretical posits aiming to explain how we perceive external objects.”

If this is correct, almost all interpretations of Locke’s theory of ideas are mistaken. Locke’s account amounts to nothing more than an unsystematic catalogue of the “ideas of which we are aware”. Indeed, the whole Essay is to be seen as an “intentionally unsystematic work”. Or so Kenny Pearce claims.

I think this is a challenging approach and certainly deserves more attention. At this point, however, I would like to address just one issue, i.e. the claim that ideas are to be seen in a “natural historical” sense. Given the evidence, I think this is correct and has been overlooked too often in attempts at making sense of book II of the Essay. But I would like to add two observations that might put a wholly different spin on Locke’s account.

(1) Natural history is not simply an account of what we “are aware” of. Locke sees his natural history of ideas as one that proceeds from simple ideas to the more complex. Starting from the simple ingredients, however, is not meant to imply that we are aware of simple ideas as givens. Locke doesn’t think that our awareness starts with simple ideas. Rather, Locke starts with simple ideas for two reasons: firstly, he wants to account for the origin of ideas; secondly, he starts with simple ideas for what one might call didactical reasons: “Because observing the faculties of the Mind, how they operate about simple Ideas …, we may the better examine them and learn how the Mind abstracts, denominates, compares, and exercises its other Operations, about those which are complex …” (II, xi, 14)

(2) Perhaps more importantly, Locke explicitly finishes this natural historical account early on and begins an entirely new discussion of ideas: here, he is interested in relations between different kinds of ideas and in what I’d call their epistemic content: “Though in the foregoing part, I have often mentioned simple Ideas, which are truly the Materials of all our knowledge; yet having treated them there, rather in the way that they come into the Mind, than as distinguished from others more compounded, it will not be, perhaps amiss to take a view of some of them again under this Consideration …” (II, xiii, 1) Thus, a great part of book II is not owing to the natural historical perspective.

The upshot is that Locke introduces two different perspectives on ideas: the natural historical one, accounting for the origin, and the epistemic one, accounting for representational content. As I elaborate in a paper of mine, I think that the former perspective focuses on the causal history of ideas, while the latter is intended as a consideration of the different kinds of representational content in our episodes of thought. In other words, the former explains how ideas originate in experience, while the latter explains how we end up taking things as something, e.g. as substances, modes or relations.

If this is correct, we should indeed acknowledge Locke’s reliance on Baconian natural history. But we should also carefully consider where Locke introduces different ways of treating ideas. After all, in conjunction with the considerations on language, Locke took his account of ideas as something that would “afford us another sort of Logick and Critick, than what we have been hitherto acquainted with.” (IV, xxi, 4)

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* Kenny Pearce regularly blogs on early modern philosophy.