Locke, John (1632–1704)

DOI: 10.4324/9780415249126-DA054-2
Version: v2,  Published online: 2017
Retrieved December 13, 2018, from

4. Abstraction, essences and kinds

Locke nowhere provides a unified account of abstraction. However, by drawing together the various passages in which he discusses this power of the understanding one can construct the general view. In abstraction ‘ideas taken from particular beings, become general representatives of all of the same kind; and their names general names, applicable to whatever exists conformable to such abstract ideas’ (Essay II.xi.9). When explaining the acquisition of the idea of whiteness Locke claims ‘the same colour being observed to day in chalk or snow, which the mind yesterday received from milk, it considers that appearance alone, [and] makes it a representative of all of that kind’ (ibid.). The salient point here is that this case of abstraction involves the formation of a type idea from a group of token ideas. Interestingly, in Locke’s classification of ideas the idea of whiteness is a simple idea. Next Locke discusses the acquisition of the idea man. This comes about when children ‘leave out of the complex idea they had of Peter and James, Mary and Jane, that which is peculiar to each, and retain only what is common to them all’ (Essay III.iii.7). This is also a case of the acquisition of a type idea from tokens, but in this case the type is a complex idea.

Finally, Locke discusses the acquisition of the idea of triangle. This comes about through the simultaneous exclusion of properties such that it is ‘neither oblique, nor rectangle, neither equilateral, equicrural, nor scalenon; but all and none of these at once’ (Essay IV.vii.9). The salient point here is that this is an instance of the acquisition of the idea of a determinable (triangular) from ideas of determinates (equilateral, scalene). Thus, Locke’s account of abstraction ranges from simple to complex ideas, from token to type ideas and from ideas of determinates to ideas of determinables.

The understanding’s power of abstraction enables it to sort things into species or kinds. In the case of modal ideas this is not difficult to do: for example, one can group the odd and the even numbers without recourse to observation. However, in the case of particular substances the correct determination of what constitutes a particular species or kind can be extremely difficult and reveals one of the main limits to our knowledge. In order to explain the nature of this problem Locke developed a distinction between real and nominal essences.

Locke defines essence as ‘the very being of any thing, whereby it is, what it is’ (Essay III.iii.15). He then distinguishes two kinds of essence. The real essence of a particular substance in the world is its inner constitution or corpuscular structure which is ‘nothing but the figure, size, and connexion of its solid parts’ on which its properties depend (Essay II.xxxi.6). The nominal essence is that cluster of ideas that constitute the abstract idea of that sort or kind. Locke’s favourite example of this distinction is gold:

the nominal essence of gold, is that complex idea the word gold stands for, let it be, for instance, a body yellow, of a certain weight, malleable, fusible, and fixed. But the real essence is the constitution of the insensible parts of that body, on which those qualities, and all the other properties of gold depend.


The problem is, however, that ‘the internal constitution, whereon their Properties depend, is unknown to us’ because it is too small to observe (Essay As a result, the mind must resort to the nominal essence of each substance in order to rank it into a particular sort. So, Locke is committed to a form of conventionalism about species: our sorting of substances starts with our ideas about them and not with their inner natures.

This much about Locke’s theory of essence is uncontested. However, scholars disagree over just how radical Locke’s conventionalism really is. Some regard him as a species nominalist. Some claim that, for Locke, the real essence of a substance is relativized to the nominal essence such that as our complex idea of a species changes, so too does its real essence. Others argue that it is the real essence that constrains the nominal essence insofar as the qualities of the real essence – unknown to us – have a ‘union in nature’ which is the causal explanation of the co-occurrence of the same cluster of ideas in our nominal essence. Thus, ‘the mind, in making its complex ideas of substances, only follows nature; and puts none together, which are not supposed to have an union in nature’ (Essay This interpretation of Locke on species sits well with Locke’s talk of perfecting our complex ideas of substances (Essay III.xi.24), for it implies that as natural philosophy advances so too will our nominal essences correspond more closely to the real essences of substances (see also Essentialism).

Whatever is the correct interpretation of Locke on species, one thing is certain: Locke was acutely aware of the empirical considerations that make it such an intractable problem. Whether it be the indeterminate nature of some species boundaries, the problem of monstrous births, the failure of reproductive isolation, or his commitment to the great chain of being, Locke acknowledged that the sorting of substances was a difficult task. As if the empirical considerations were not hard enough, humans also have a propensity to misuse words.

Locke claims that words are signs of ideas and ideas are signs of things in the world or the mind. Thus, ‘the idea which an English-man signifies by the name swan is white colour, long neck, red beak, black legs, and whole feet, and all these of a certain size, with a power of swimming in the water, and making a certain kind of noise’ (Essay II.xxiii.14). Locke’s choice of the word ‘swan’ is a nice illustration of the contingent nature of our nominal essences, for in 1698 Locke learnt from a correspondent of ‘the discoveries of the Dutch of black swans’ which were almost certainly found on the west coast of Australia (Locke 1976–89, 6: 480). The example also provides an entrée into Locke’s views on the nature of propositions and knowledge.

Citing this article:
Anstey, Peter. Abstraction, essences and kinds. Locke, John (1632–1704), 2017, doi:10.4324/9780415249126-DA054-2. Routledge Encyclopedia of Philosophy, Taylor and Francis,
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