Context

The last three sections of Part I are applications of the general principles discovered in the first four sections. In the previous section, the author has treated our ideas of relations. In the present section, he turns his attention to the ideas of substances and their modes.

Background

The concept, or idea, of substance has a long and complex history in philosophy before Hume. Here we will discuss some aspects of the concept of substance that are relevant to Hume’s account of it.

Substance and Accident

Hume calls attention to two correlative notions: substance and accident, as well as to the notion of mode. By the late medieval period, the term ‘accident’ was used in the way we now use the term ‘property.’ An accident is necessarily an accident of a substance. It was said that the relation between accident and substance is that accidents “inhere in” substances. Because of the dependence of accidents upon substances, substances were thought to be in some way “more real” than their accidents. For example, in the 1609 A Compendium of Philosophy in Four Parts, Eustachius a Sancto Paulo writes, “A substance is said to be more properly an entity than any accident, since no natural power can enable accidents to exist unless they inhere in or belong to a substance” (First part, Treatise III, Discourse I, Question 2). (Note, however, that it was commonly held that a divine power could cause accidents to exist without inhering in a substance. This allowed an explanation of the existence of the accidents of bread and wine after their substance has been changed into the body and blood of Christ.)

Descartes

Descartes understood substance as “a thing which exists in such a way as to depend on no other thing for its existence” (Principles of Philosophy, Part One, Section 51). He largely abandoned the term ‘accident’ (though it is defined as a “universal,” which in turn is merely a “mode of thinking,” in Principles, Part One, Section 59). In the place of ‘accident,’ Descartes substitutes the term ‘attribute,’ which is a general way of referring to “what is in a substance” (Principles, Part One, Section 56). So as with the medievals, there is an asymmetrical relation of dependence between substance and what is in it. Descartes went on to define ‘mode’ as an attribute which is an “affection” or “modification” of a substance. For example, if my mind is a substance, thought is an attribute (indeed, the principal attribute) of my mind, whereas my current thought of Descartes is a mode of my mind: the way it currently exists. (Note finally that Descartes rejected the possibility of “real accidents” existing without substance, for which he was censured by various Catholic authorities.)

Locke

In Book II, Chapter 23 of the Essay, Locke approaches the matter from the standpoint of the content and origin of the complex idea of substance. As all complex ideas are composed of simple ideas, Locke begins by noting a feature of some simple ideas, that they “go constantly together.” This gives rise to the presumption that the ideas “belong to one thing.” Thus, we form ideas of a horse or a stone, which are “particular substances” consisting of ordinary observable qualities that are commonly known better by “a smith or a jeweller” than by a philosopher. Locke summarizes his account by stating that “our specific ideas of substances are nothing else but a collection of a certain number of simple ideas, considered as united in one thing.”

But Locke does not stop here. The idea of a substance contains more than the ideas of the various qualities of the thing. With his predecessors, Locke believed that the qualities of things are dependent on something: “not imagining how these simple ideas can subsist by themselves, we accustom ourselves to suppose some substratum in wherein they do subsist, and from which they do result.” Locke states that “the notion of pure substance in general” refers to the substratum, or “a supposition of [one] knows not what support of such qualities which are capable of producing simple ideas in us; which qualities are commonly called accidents.” Thus, the idea of substance in general is “obscure and relative,” as well as being “confused.” This “secret abstract nature” is of no use in classifying substances under different kinds (such as man or stone).

Locke confesses that he uses the word ‘mode’ in a novel way. Modes are “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” (Essay, Book II, Chapter 12). At first glance, this seems to be equivalent to what were traditionally known as “accidents.” But Locke uses the word ‘quality’ in place of the traditional ‘accident.’ We might think of modes instead as ways of existing of the qualities of substances. Supposing an egg to be a substance, and unity to be a quality of substances, there being a dozen eggs is a mode of the substances, generated by aggregating the unities. Another example is beauty, “consisting of a certain composition of color and figure, causing delight to the beholder.”

Berkeley

One of the central tenets of Berkeley’s philosophy was his denial the existence of “pure substance in general,” as well as his denial of the possibility of particular material substances. The argument, as found in the Principles of Human Knowledge, can be summarized as follows. The notion of a “support” of qualities of substances is a mere metaphor, as is the notion of “inherence.” Nonetheless, Berkeley did not deny that the qualities of corporeal things (men, stones, etc.) do not exist independently.

Berkeley had argued against Locke that the qualities of corporeal things are not represented by ideas, but rather are ideas. And ideas depend for their existence on the mind: an idea exists only insofar as it is perceived by a mind. The relation of being perceived eliminates the need for a substratum for the qualities of things, because as ideas they depend on a perceiver. Corporeal things are nothing more than collections of ideas. For example, “a die seems to me nothing distinct from those things which are termed its modes or accidents” (Section 49). As for Locke’s question concerning why the ideas “go together” as they do, Berkeley ultimately appeals to God’s design (see, e.g., Section 65).

To be sure, the word ‘substance’ may be applied to them in this “vulgar” sense, “but if it be taken in a philosophic sense—for the support of accidents or qualities without the mind—then indeed I acknowledge that we take it away, if one may be said to take away that which never had any existence, not even in the imagination” (Section 37).

Minds, however, are not collections of ideas, because ideas depend on them. Thus they play the traditional role of substances, only without the traditional relation to accidents, qualities or attributes. A quality is not an accident of the mind, but it is an idea perceived by the mind.

The Treatise

1. Much of the reasoning of many philosophers depends on a distinction between substance and accident, and these philosophers think that they have clear ideas of substance and of accident. But the author asks “whether the idea of substance be deriv’d from the impressions of sensation or reflection?” If it is an impression of sensation, then it must be associated with one of the senses, e.g., “if it be perceived by the eyes, it must be a colour.” But in that case, substance would be a color (or one of the other impressions), which none of the philosophers just mentioned would allow. [Strictly speaking, the idea of substance would have to resemble the corresponding impression of sensation, and it would refer to the object of the impression, such as a color.] This leaves only impressions of reflection as the source of the idea of substance, “if it really exist.” However, the latter kind of impressions are passions or emotions, “none of which can possibly represent a substance.” The conclusion that must be drawn is that “we have . . . no idea of substance, distinct from that of a collection of particular qualities. Thus, when we talk or reason about substance, we are only talking or reasoning about a collection of particular qualities.”

2. In this paragraph, the author examines the idea we have of substance, and in the next our idea of mode. In both cases, the idea is about a collection of qualities. [From the examples given, it is clear that the author has in mind substance and mode as general kinds of things: gold, a dance, beauty.] The ideas of these qualities are united by the imagination and are given a name, which allows us to recall that collection of qualities to ourselves or to others. The way in which this takes place is very different in the cases of substances and modes. Substances are supposed to be composed of qualities but to be more than just the sum of their qualities. One view [Locke’s] is that the qualities making up a substance are “referr’d to an unknown something, in which they are suppos’d to inhere.” This view is a fiction. A more modest view is that the qualities are “suppos’d to be closely and inseparably connected by the relations of contiguity and causation.” On either of these views, we may begin with a certain collection of qualities which are connected in a certain way, and then add to the collection new qualities which we discover to stand in the same connection. We might at first have an idea of gold as which is a collection of a yellow color, a certain weight, the ability to be shaped [as into rings: the property of malleability], and the ability to be melted [fusibility]. When it is discovered that something with these qualities can also be dissolved in aqua regia [a mixture of hydrochloric and nitric acids], that quality is added to the others and supposed “to belong to the substance as much as if its idea had from the beginning made a part of the compound one.” The reason that a new quality can be added on a par with the original ones is that the “chief part of the complex idea” of a substance is “the principle of union,” and not any particular quality.

3. On the other hand, no new qualities may be added to the collection of qualities that makes up a mode. There are two kinds of modes. The first is one in which the qualities making up the collection are dispersed among various objects, as with a dance, the idea of which includes different dancers. So there is no union based on contiguity and causation [let alone an “unknown something”], and hence no basis for adding new qualities. The second kind of mode is one in which the qualities are united in one object, but in such a way that “the uniting principle is not regarded as the foundation of the complex idea.” Beauty would be an example of a mode of a second kind. [The union of the qualities that make a person beautiful is not that which makes the person a substance. There is nothing about the former union which admits of allowing new qualities to be added to it in the way that new qualities can be added to the object qua substance.] If a new quality were to be added to the complex making up the mode, we would be talking about a different mode, which would have to be given a different name.

The Enquiry

There is no extended discussion of substance in the Enquiry. Substance is only mentioned a few times, and mode not at all. One place where substance plays a role is in the discussion of the idea of necessary connection, in Section 7. There, Hume implies that we do not know the “secret nature” of either mental or bodily substance, and hence that we are not entitled to claim that one has the power to bring about a change in the other. At the end of Part 2 of Section 12, Hume advances Berkeley’s skeptical argument against the existence of material substance. If all sensible qualities are in the mind, it might be held there could still exist “matter” which is mind-independent. Hume attacks the notion of a substratum of no sensible qualities of things. The notion of “a certain unknown, inexplicable something, as the cause of our perceptions” is “a notion so imperfect, that no skeptic will think it worth while to contend against it.”