Locke on Substance
Some Lecture Notes

© by Dr. Jan Garrett

Last modified February 27, 2007

Importance of the Idea of Substance

Roughly, substances are enduring things whose presence gives continuity and even meaning to a thinker's vision of reality. Almost all major philosophers have a felt a need to say something about substance, even if they did not use the term, for if there were nothing continuous of this sort, then everything would undergo constant change, and thus the world would be chaotic and fundamentally unintelligible.

For almost every philosopher since Aristotle who speaks of substance, the existence of a substance makes possible the existence of accidental features, features the thing may have or lack. An accident exists only if there is a substance to which it is attached. Thus, for Descartes, doubt is an accident which depends upon mental substances for its existence.

Locke on the Origin of the Idea of Substance

According to Locke in Book II of his Essay Concerning Human Understanding, the Mind, observing the ideas it is furnished with, notices that various simple ideas go together, as it were, in groups, and are thus presumed to belong to one thing. Words--nouns, primarily--play a role here, as they are developed to refer with convenience to such things.

Not imagining how these simple ideas can subsist by themselves, we accustom ourselves, to suppose some substratum wherein they do subsist, and from which they do result, which therefore we call substance. (Chapter 23, Sect. 1)
Continuing, Locke writes,
if anyone will examine himself concerning his notion of pure substance in general, he will find he has no other idea of it at all, but only a supposition of he knows not what support of such qualities which are capable of producing simple ideas in us; which qualities are commonly called accidents. (Sect. 2)
In what do qualities like color and weight inhere? the solid extended parts. But in what do solidity and extension inhere? We are at a loss to say, other than something "we know not what" which underlies the observable qualities.

Locke's views on substance need to approached with a certain amount of caution. He does not deny that we have the idea of substance, as a kind of support of qualities. But he stresses how limited this idea is.

In a few years, George Berkeley will accuse Locke of not going far enough; since we have no sense impressions concerning material substance, B. will say, we really have no idea of it at all and we should dismiss the idea of material substance altogether. Then David Hume will say that B. too failed to go far enough, for we have no sense impressions of mental substance or soul either.

Now, Locke would agree with Hume to this extent: we are in the same position with respect to mental substance as with material substance. We have internal evidence of the operations of spirit, such as thinking, fearing, reasoning, which are accidents which we suppose to inhere in a mind or soul, a mental substance, but

we have as clear a notion of the substance of spirit, as we have of body; the one [is] supposed to be (without knowing what it is) the substratum to those simple ideas we have from without; and the other [is] supposed (with a like ignorance of what it is) to be the substratum to those operations, which we experiment [experience] in ourselves within. (Chapter 23, Sect. 5)
Yet, unlike Berkeley and Hume, Locke refuses to depart from common sense so radically as to deny, or toy with denying, the existence of material and mental substances.

We do, however, have complex ideas of substances, says Locke, as the collection of primary, secondary and tertiary qualities that are typically linked in the supposed substrata:

Whatever . . . be the secret and abstract nature of substance in general, all the ideas we have of particular distinct sorts of substances are nothing but several combinations of simple ideas, coexisting in such, though unknown cause of their union as makes the whole subsist of itself. 'Tis by such combinations of simple ideas, and nothing else, that we represent particular sorts of substances to ourselves. (Chap. 23, Sect.6)
Most of these qualities are tertiary ones, which is to say, the active or passive powers of things (Chap. 23, Sections 8-10). These powers are the capacities of things to behave in certain ways under certain circumstances, when they are brought together with other things or experimented with in various ways. Gold, for example, is soluble in aqua regia. Loadstone, a naturally occurring magnetic rock, has the power to draw iron.

Inadequacy of Our Ideas about Substances

The importance of this point regarding tertiary properties of material substances should not be underestimated. It leads Locke to make some interesting observations about the inexhaustibility and inevitable inadequacy of our ideas regarding substances.

In Book II, chapter 31 he distinguishes between adequate and inadequate ideas: ideas are adequate just in case "they perfectly represent those archetypes [originals] which the mind supposes them taken from; which it intends them to stand for, and to which it refers them." (Section 1) Inadequate ideas are incomplete representations of those originals to which they are referred.

All our simple ideas, Locke says, are adequate (Section 2). They are, after all, nothing but the effects of powers in things, fitted and ordained by God, to produce certain sensations in us. We are sure they agree to the reality of things. When Locke says that all our simple ideas are adequate, he means our ideas of primary, secondary and tertiary qualities of things.

(You might think that this contradicts his view that ideas of secondary qualities, like yellow or sweet, do not resemble these ideas' causes that exist in external things. Locke does not mean to retract this view. What he means is that there is a reliable correlation, attributed ultimately to the goodness of God, between some really existing features of the cause of these ideas and the sensory ideas themselves as they appear in our mind.)

Our complex ideas of substances, however, are all inadequate. "For there desiring to copy things as they really do exist; and to represent to ourselves that constitution on which all their properties depend, we perceive our ideas attain not that perfection we intend." (Chapter 31, Sect. 3) One major reason that our ideas of substances are and will remain inadequate is that we can never know all the active and passive powers which a given kind of material thing (such as gold) possesses (though a specialist will know many more than the man on the street and therefore have a different idea of the substance). (Chapter 31, Sect. 8:

The simple ideas whereof we make our complex ones of substances are all of them (bating only the figure and bulk of some sorts) powers; which being relations to other substances we can never be sure that we know all the powers that are in any one body till we have tried what changes it is fitted to give to or receive from other substances in their several ways of application: which being impossible to be tried upon any one body, much less upon all, it is impossible we should have adequate ideas of any substance made up of a collection of all its properties.
For Locke all our ideas come ultimately from sense-experience and tend to be, at best, like copies of the surfaces of things. And when you think about it, there's no certainty that the ideas we get about a thing reveal its true essence or core.

Nominal v. Real Essences

Locke, in fact, does not believe we can know the inner nature of things. We could know gold for example only as a yellow metal, ductile, heavy, soluble in aqua regia, etc. But we couldn't know how these attributes, which we experience, arise as a result of its internal structure. He takes up this problem in Books iii and iv of the Essay. In Book iii he introduces the distinction between nominal and real essence of things. The nominal essence is captured in the definition of things by their empirical qualities; the real essence, which is the nature of the thing as it is in itself, is beyond our grasp; it seems to be in about the same situation as the "I know not what" that underlies qualities. We seem to have to assume it is there, but confess not to be able to know it.

Locke seems a bit ambiguous regarding just why we cannot know it. Sometimes it sounds as if we could know it if only we had much more powerful microscopes, i.e., more powerful enhancements of our senses. This is an interesting idea, since we do today have just such instruments, and our scientists will sometimes say that now we know what gold really is (its atomic structure, say, the number of protons and electrons which atoms of gold have) as well as much more about how it affects other things and produces events which we observe through the senses.

At other times Locke's doubts about discovering the true nature of matter seem more radical: enhance the powers of the senses as you will, he seems to say, you will still never see into the hidden heart of matter, for in your observations you only have access to the effects, not to the causes. To which one might add, reasoning from effects to causes is at best probable; even if we have a theory concerning the causes from which all the known effects can be deduced, there could well be another theory which would do so as well, and we would have no way to be sure which of the two was correct.


bating = with the exception of

aqua regia = a mixture of nitric and hydrochloric acid that dissolves gold or platinum