Locke on Modes, Substances, and Knowledge

Locke on Modes, Substances, and Knowledge R. S. WOOLHOUSE IN A RECENT ARTICLE Christopher Aronson and Douglas Lewis "describe what Locke believes the difference is in ontological status between mixed modes and substances'. 1 They conclude that 'a substance has a real essence which makes a unity of the properties which constitute it.... On the other hand . . . a mixed mode . . . has no real essence which makes a unity of the properties which constitute it'. 2 Their article was written in the light of an earlier one in which David L. Perry, having pointed out that Locke's mixed modes are archetypes and adequate (a fact which, according to Aronson and Lewis [p. 196], follows from mixed modes' having no real essence), says that 'these features are the basis for Locke's attempt to account for a portion of our alleged knowledge of absolutely certain yet instructive propositions'. 3 However, he concludes: There is little difficulty in appreciating the necessary truth of trifling propositions, but we must view as problematic at best the purported necessity of instructive propositions . How can we intuit or demonstrate necessary agreements and disagreements between ideas which are grounded, but not contained, in the nature of those ideas? . . .--Locke evidently recognized no problem in this regard; at least he proposed no solution. (pp. 234-235) Aronson and Lewis agree with Perry about this, and so urge that 'It seems reasonable to suggest therefore that Locke never intended these features of ideas of mixed modes to provide an account of the possibility of this kind of knowledge at all' (p. 193). This line of thought is, I suggest, mistaken:, (1) It is simply false to say that for Locke any difference between modes and substances lies in the former's not 1 'Locke on Mixed Modes, Knowledge, and Substances', Journal of the History of Philosophy, VIII, 2 (1970), 194. 2 Ibid., p. 195; see also lower on this page and pp. 196, 197. a 'Locke on Mixed Modes, Relations, and Knowledge', Journal of the History o] Philosophy, V, 3 (1967), 219. 4 Much of my argument is based on what Locke says about geornetrical figures which, at least officially (II.xiii.5), are simple, not mixed modes. But, as Perry observes (p. 219), [417] 418 HISTORY OF PHILOSOPHY having, and the latter's having, a real essence. In a good number of passages Locke speaks of the real essence of modes, s (2) Since Locke says that modes (like substances) do have real essences the adequacy of our ideas of them (and the inadequacy of our substance-ideas) cannot follow from their not having them (and substances' having them). What it does follow from is, for Locke, our knowledge of modal real essences (and our ignorance of substantial ones). (3) The fact that we know modal real essences, that our mode-ideas are adequate, is intended by Locke to account for our knowledge of instructively necessary propositions. (4) Locke does not leave 'unexplained the . . . possibility of arriving at certain, yet instructive propositions' (Perry, p. 235). The support for this is as follows: (1') Modes do have real essences, for Locke tells us that 'the names of mixed modes always signify . . . the real essences of their species'.6 He speaks of modal real essences also at II.xxxii.24, III.iv.3, xi.15, IV.xii.7-9, vi.4; and at IH.iii.18 where, having distinguished between real and nominal essence, he observes that 'in the species of... modes, they are always the same .... Thus, a figure including a space between three lines, is the real as well as nominal essence of a triangle'. (2') Something must first be said here about the notion of real (and nominal) essence as applied by Locke to substances. All natural things 'have a real, but unknown, constitution of their insensible parts; from which flow those sensible qualities which serve us to distinguish them one from another, according as we have occasion to rank them into sorts, under common denominations' (III.iii.17). And, as is well known, 'the real constitution of the parts' of gold (e.g.) is its real essence, which Locke conceives of as analogous to the internal...