1.1 Knowledge of the external world in Locke’s Essay
In the pop-history of philosophy, Locke is guilty of many philosophical mistakes. Topping the chart of Locke’s greatest philosophical blunders is his discussion of knowledge of the
existence of the external world, which is widely regarded as obviously problematic.52 On the
one hand, Locke is no skeptic. He repeatedly insists that there are, and we know that there are, bodies around us (cf. IV.ii, IV.iv, IV.ix, IV.xi). On the other hand, given that all we perceive are ideas, it isn’t clear how we could ever know that anything exists besides ideas. Worse, Locke’s very definition of knowledge seems plainly inconsistent with knowledge of the existence of anything besides our own mind and ideas. Knowledge, according to Locke,
is the perceived agreement of ideas. How, nearly every reader of the Essay has wondered, can
we know that something exists beyond our ideas by perceiving an agreement between ideas?
52 For example, see Ayers, (1991), Woolhouse (1994), Mattern (1998), Jolley (1999), Bennett (2003), Rickless (2006). For slightly more charitable, though ultimately critical, interpretations see Bolton (2004), Owen (MS),
Locke does allow for an idea of existence, but it took Hume all of a footnote to dispatch the
viability of an approach to knowledge of existence through an idea of existence.53
! In this chapter and the next I will offer a new account of how the second problem
above can be solved. By treating Locke as engaged in the naturalized epistemology described in the Introduction, I will show that Locke can and does offer an account of knowledge of the existence of the external world in the terms of his definition of knowledge as the perception of agreement between ideas. Specifically, I will argue that such knowledge consists in the perception of agreement between a simple idea of sensation and a complex idea of substance. Lingering skeptical worries due to Locke’s claim that all we perceive are ideas will have to wait until the final chapter of the dissertation.
! The problem of reconciling Locke’s account of knowledge in general with knowledge
of the external world breaks down into the following three parts: (a) Which ideas agree in knowledge of the external world?
(b) What is it for ideas to agree?
(c) What does the agreement of those ideas have to do with knowledge of the external
world?
By answering these questions we will have a new answer to a problem that has long been regarded as unsolvable. Indeed, the secondary literature is nearly unanimous in holding that Locke’s definition of knowledge cannot accommodate knowledge of the external world. On
53 In a footnote to his official definition belief at 1.3.7.5 of his Treatise, Hume writes: “We may here take occasion to observe a very remarkable error, which being frequently inculcated in the schools, has become a kind of established maxim, and is universally received by all logicians. This error consists in the vulgar division of the acts of the understanding into conception, judgment, and reasoning, and in the definitions we give of them. Conception is defined to be the simple survey of one or more ideas: judgment to be the separating or uniting of different ideas: reasoning to be the separating or uniting of different ideas by the interposition of others, which shew the relation they bear to each other. But these distinctions and definitions are faulty in very considerable articles. For, first, it is far from being true, that, in every judgment which we form, we unite two different ideas; since in that proposition, God is, or indeed, any other which regards existence, the idea of existence is no distinct idea, which we unite with that of the object, and which is capable of forming a compound idea by that union...”
one side of this debate are those who claim that Locke’s epistemology fails to account for knowledge of the external world because such knowledge doesn’t fit with his definition. On the other side are those who attribute a bifurcated account of knowledge to Locke: one half is provided by his definition of knowledge, the other half is a tacit reliabilism that covers knowledge of the external world. Over the course of this chapter and the next I will develop my answers to the three questions and show the falsity of this dilemma in the literature. For now, I briefly state my answers to these questions as a guide to what’s to come.
(a) The ideas which agree in knowledge of the external world are a complex idea of a substance and a simple idea of sensation.
(b) Ideas agree when one literally contains the other as a part. In the case of
knowledge of the external world, the complex idea of a substance contains the simple idea of sensation.
(c) The agreement of these ideas is relevant to knowledge of the external world because their agreement accounts for two features of knowledge of the external world Locke believes any analysis of such knowledge must account for: first, knowledge of the external world obtains in sensory experience; second, knowledge of the external world is founded on our awareness of our passivity in sensory experience.
How to develop these answers presents a difficult expository challenge. Each answer sheds light on the others and makes their significance and force easier to grasp. The other side of that fact is that the first answer I develop will not be fully defended until all the answers are on the table. Nevertheless, we must start somewhere.
! To choose a starting point I will follow the recipe for expositing Locke’s
epistemology laid out in the Introduction. According to that recipe we want to first exposit the relevant parts of Locke’s theory of ideas. To exposit the relevant parts of Locke’s theory of ideas is just to exposit the genetic structure of the relevant ideas. The ideas relevant to knowledge of the external world for Locke are a complex idea of a substance and a simple
idea of sensation. A full defense of that claim must wait.54 The second step is then to examine the containment relations that are revealed by our account of the genetic structure of the relevant ideas to see what knowledge is had by perceiving such ideas. Finally, the last step is to explain how the perception of such ideas accounts for the knowledge in question.
! In accord with the recipe, I will now explicate the parts of Locke’s theory of ideas
relevant to knowledge of the external world: complex ideas of substances and simple ideas of sensation. The aim of this chapter is to give an account of Locke’s categories of complex ideas of substances and simple ideas of sensation that will prepare us to understand their role in Locke’s account of knowledge of the external world. I will argue for the following
understanding of each category of ideas. Complex ideas of substances are ideas of things which exist and affect our mind by the production of simple ideas in our understanding. Simple ideas of sensation are the appearances by things to the mind and constitute the
interface between mind and world. I will argue for these understandings by examining the
genetic structure of these ideas and their place within Locke’s naturalized epistemology— how Locke uses these categories of ideas to analyze our experiences and thoughts.
1.2 Locke on complex ideas of substance
! To properly understand Locke’s discussion of our complex ideas of substance it is
important to keep two kinds of distinctions in mind. First, we must be careful to distinguish the programmatic and polemical dimensions of Locke’s discussion of our ideas of
substances. The programmatic dimensions of Locke’s discussion of our ideas of substances
54 Here we come to an unsatisfying aspect of beginning with question (a): I must simply state what I take the ideas to be. Only once we have a grasp of answer to question (c) will we have a satisfactory defense of my answer to question (a). However, the answer to (c) depends on the answer to (b) and I believe it will be easier to understand the answer to (b) and (c) after gaining some familiarity with Locke’s genetic theory of ideas since his account of knowledge is in the terms of his genetic theory of ideas.
are Locke’s efforts to accommodate our ideas of substances within his program of illustrating their genetic structure. Locke’s programmatic discussion of our ideas of substances therefore has two components. First, Locke articulates some characteristic features of thoughts of substances that distinguish them from thoughts of modes or relations. Second, Locke illustrates the genetic structure of thoughts of substances. Having given the characteristic or distinguishing features of thoughts of substances, Locke then illustrates how such thought can be understood as perceiving a complex idea with a genetic structure that differentiates it from other kinds of complex ideas. In displaying the genetic structure of complex ideas of substances, Locke reveals how complex ideas of substances can be understood as consisting in nothing but simple ideas received in sensation and reflection put together by operations of the mind.
! The polemical dimension of Locke’s discussion of ideas of substances has to do with
the controversial conclusions he draws from his account of the genetic structure of ideas of substances. One conclusion, for example, is that our ideas of mind and matter are on equal footing. Neither offers us anymore insight into the essences of minds or bodies, or is any less mysterious, than the other. A second and related conclusion is that previous accounts of our epistemology of substance are mistaken in a way that we will detail shortly. To preview: our epistemic discourse regarding the classification of substances into kinds is guided by our nominal essences of kinds, ideas of their qualities, rather than ideas of their real essence.
! A second kind of distinction that is important to track in Locke’s discussion of
complex ideas of substances has to do with the different ways in which Locke uses the phrase, ‘idea of substance’. We can distinguish at least five different uses. To tease them apart, we can begin with Locke’s introduction of ideas of substances:
(SubA): The ideas of substances are such combinations of simple ideas, as are taken to represent distinct particular things subsisting by themselves, in which the
supposed, or confused idea of substance, such as it is, is always the first and chief. (II.xii.6/165)
Consider the first part of Locke’s description. Ideas of substances are ideas of things, or
objects. Things, or objects, are special in that they exists on their own. Substances only depend on themselves for existence. Ideas of modes and relations, by contrast, are ideas of things with dependent existence. Locke’s account of modes contains a complementary definition in terms of dependence: “[M]odes I call such complex ideas, which however compounded, contain not in them the supposition of subsisting by themselves, but are considered as dependences on, or affections of substances” (II.xii.4/165). Locke’s examples
of modes and substances confirms that the distinction is supposed to track things or objects,
on the one hand, and that which depends on substances for their existence. Among Locke’s list of modes are: triangle, gratitude, beauty, a dozen, theft, and murder (II.xii.4). Among Locke’s examples of substances are a man, a sheep, and lead (II.xii.6).
! The second half of (SubA) is potentially confusing and so must be addressed. Locke
seems to be saying that the idea of substance is the ‘chief’ component of ideas of substances.
To clarify, Locke follows (SubA) with:
(SubB): Thus if to substance be joined the simple idea of a certain dull whitish
color, with certain degrees of weight, hardness, ductility, and fusibility, we have the idea of lead; and a combination of the ideas of a certain sort of figure, with the powers of motion, thought, and reasoning, joined to substance, make the ordinary idea of a man. (II.xii.6/165)
Locke’s point is as follows. Our complex ideas of substances have several components. Some of those components are ideas of properties, or qualities, like color, ductility, thinking, etc. Of course, ideas of modes can include such ideas as well. What distinguishes our ideas of
Thus, the complexity of ideas of substances is evident in their introduction in the Essay. They are combinations of ideas of qualities with the idea of substance.
! The role of the idea of substance in complex ideas of substances emerges by bringing
the two halves of (SubA) together. Ideas of substances differ from ideas of modes or relations
in that they are ideas of things which do not depend on anything else for their existence. This feature of our ideas of substance is accounted for within Locke’s theory of ideas by the fact that ideas of substances are alone in having as a part the idea of substance. So, whatever the idea of substance is, its role in our ideas of substances seems to be to mark the unique feature of ideas of substances: that they are ideas of independently existing things on which modes and relations depend for their existence.
! Locke’s introductory remarks concerning ideas of substances has an additional source
of potential confusion over and above the double use of ‘substance’. The second potential
confusion has to do with Locke’s examples of substances. In (SubA) Locke calls ideas of
substances ideas of “distinct particular things”. In (SubB), however, Locke’s first example
doesn’t appear to be an example of a distinct particular thing, but instead of a kind of thing: lead. Locke writes that combining the idea of substance with certain ideas of qualities gives
us our substance idea of lead and not simply our idea of a particular hunk of lead. Some
commentators make heavy weather of this text. Bolton (1998), for example, takes this as part
of an argument against the claim that, for Locke, ideas of substances are ideas of particular
individuals. Bolton (1998) argues that our complex ideas of substances are ideas of natural
kinds.55 As I will argue in section 1.2.3 below, Bolton’s reading, like many other
55 “Although the expression ‘distinct particular things’ might naturally be taken to mean Aristotelian individuals, or countable things, that interpretation is ruled out at once by the appearance of lead, a sort of
interpretations of Locke on substance, understands Locke’s discussion of ideas of substance to articulate a metaphysics of substance. This is, I will argue, a mistake.
! It seems best to interpret the fact that Locke’s examples of substances in II.xii.6 range
over an idea of lead (a kind of thing) as well as an idea of a man (a particular thing) to be evidence that there is another important ambiguity in Locke’s uses of the phrase ‘idea of substance’. Locke’s category of complex ideas of substances provides the category under which Locke’s theory of ideas analyzes of all thoughts and experiences of things, or objects. Our thought and experience of things or objects are varied, of course. We can have a thought or experience of a particular thing, such as the particular daffodil outside my now. Or, we can think of kinds of things, such as daffodils. Within Locke’s theory of ideas, both of these kind of ‘thing’-thoughts are analyzed as the perception of complex ideas of a substances. The distinguishing feature of all of these ideas is that they include in them the idea of substance; it is by virtue of having the idea of substance as a part that they are all ideas of substances.
! In addition to these four uses of the phrase ‘idea of substance’ there is one more,
though it is almost exclusively found in philosophy. This use of the phrase ‘idea of
substance’ is an idea of a metaphysical kind which is distinct from modes or relations. It is an abstract idea of substance in general. Presumably, it is abstracted from the idea of substance which is a characteristic component of ideas of substances. Locke often uses the phrase this when criticizing the explanatory weight other philosophers put on such an idea or
metaphysical kind. For example, in the context of considering whether space is a mode or a substance, Locke writes, “If it be demanded (as usually it is) whether this space void of body, be substance or accident, I shall readily answer, I know not: nor shall be ashamed to own my ignorance, till they that ask, shew me a clear distinct idea of substance” (II.xiii.17/174).
Locke’s complaint here is about the metaphysical kinds substance and accident. Locke professes to not feel the need to come up with an answer to the metaphysical nature of space
because the ideas metaphysical kinds, at least that of substance, are confused.56
! So far, then, we have five closely related uses of the phrase ‘idea of substance’. By
‘idea of substance’, Locke may mean:
Idea of substance1:! The component idea which distinguishes complex ideas of
! ! ! substances from other complex ideas.
Idea of substance2:! Complex ideas of substances, both particular individuals
! ! ! and kinds of substances
Idea of substance3: ! An idea of a particular, individual thing.
Idea of substance4:! An idea of a kind of thing.
Idea of substance5: ! An abstract idea of a metaphysical kind, distinct from other
! ! ! metaphysical kinds such as mode or relation.
Ideas of substances2 contain, as a part, an idea of substance1. This is what makes them ideas
of substances2. Ideas of substances3 or substances4 are sub-cases of ideas of substances2. So,
ideas of substances2 can be divided into ideas of a particular individuals (ideas of
substances3) or general ideas of a kinds of individuals (ideas of substances4). It is by virtue of
containing the idea of substance1 as a part that ideas of substances3 or substances4 are ideas
of substances2, as opposed to complex ideas of modes or relations. What differentiates ideas
of substances3 from ideas of substances4 has to do with another part of their genetic structure.
Presumably, the operation of the mind Locke calls ‘abstraction’ is an important distinguishing
56 Other uses of this phrase can be found in II.xiii.18-20, and in II.xxiii, entitled ‘Of our complex ideas of substance’. For example, from Locke’s discussion in II.xxiii: “the idea then we have, to which we give the