Locke, John (1632–1704)

DOI: 10.4324/9780415249126-DA054-2
Version: v2,  Published online: 2017
Retrieved September 22, 2018, from

7. Natural philosophy

On the question of assenting to propositions about matters of fact beyond the limits of our senses, Locke claims that in these cases we must resort to reasoning by analogy. He has a broad conception of analogical reasoning encompassing both inferences based on the principle ‘same effect, same cause’ and a principle of continuity. As for the first sort of analogy, he refers to the production of heat by rubbing two bodies together and inferring from this that the heat of burning matter is the violent agitations of the imperceptible corpuscles from which it is constituted. For the second he argues that from the gradations we perceive in the qualities of living things, we can infer that there is a great chain of being (Essay IV.xvi.12).

These kinds of analogical reasoning can give rise to hypotheses and even the discovery of new truths and the production of useful artefacts. Yet one should not conclude from this that Locke is sanguine about the prospects for natural philosophy or that he had a kind of proto-hypothetico-deductive method. For, a careful analysis of his writings on natural philosophy and their context reveals that he was committed to the new methodology of the experimental philosophers within his ambit. Like them, he gave priority to observation and experiment over premature speculation based upon hypotheses. And like them, he argued for the importance of accumulating a broad base of matters of fact through the application of the Baconian method of natural history before resorting to theorizing (see Bacon, Francis (1561–1626)). However, unlike many of them he was highly pessimistic about the prospects of natural philosophy ever having the status of a demonstrative science like geometry. Thus, while he regarded the corpuscularianism promoted by the likes of Boyle as the most intelligible speculative theory of matter, he very much doubted that we would ever gain epistemic access to the determinate qualities of actual corpuscles.

Without knowledge of the microstructure of particular substances it is impossible to know their real essences and this leads us back to the problem of species. Yet, for Locke, the problems for natural philosophy run still deeper, for even if we had knowledge of real essences of particular sorts of substances, there are unresolvable conceptual problems with the very notion of matter itself.

For example, for Locke, material substance is solid and extended. He defines extension as cohesion of solid parts. Yet he is at a loss to explain the difference between mere contiguity and cohesion. He presents a battery of arguments to show that cohesion cannot result from the pressure of an ambient fluid. And his views about the individuation of substances preclude any form of interpenetration – two substances of the same type cannot occupy the same place at the same time – but just what the cause of cohesion is remains a mystery (Essay II.xxiii). He concludes that we know as little about matter as we do about spirits.

Nevertheless, Locke does have positive views on the nature of material qualities; indeed, on this point he consolidated recent developments in the new, post-Aristotelian theory of qualities. Locke distinguished between the primary qualities of material bodies and their secondary qualities. According to the orthodox interpretation of Locke, primary qualities are those qualities that satisfy two criteria: inseparability and resemblance. The inseparability Locke has in mind is conceptual: one cannot conceive of a material body without some shape, size and degree of motion or rest.

As for resemblance, for observable material bodies, the primary qualities are those qualities that resemble our ideas of those qualities. Thus, my idea of the rectangular shape of the desk in front of me resembles the actual shape of the desk. Secondary qualities, by contrast are conceptually separable: one can conceive of a body that has no colour. Nor do our ideas of secondary qualities resemble their real world correlates. According to Locke, there is nothing in snow resembling the idea of white. Rather, the secondary quality of whiteness is the power that a body has to cause the idea of white in us. For Locke, secondary qualities ‘are in truth nothing in the objects themselves, but powers to produce various sensations in us, and depend upon those primary qualities, viz. bulk, figure, texture, and motion of parts’ (Essay II.viii.14). (See also Primary–secondary distinction)

The corpuscular theory of matter went some way to explaining how a secondary quality such as colour depends upon the texture or arrangement of parts of a body. However, not all the qualities of material bodies could be classified as either primary or secondary. For Locke, the two most problematic qualities were gravity and thought. It is telling that the term ‘gravity’ does not appear in the Essay, even though Locke discusses universal attraction in Some Thoughts Concerning Education and in the Stillingfleet correspondence. In the former he speaks of gravity as ‘impossible to be explained by any natural operation of matter’ (Locke [1693] 1989: 246) and in the latter he says that the power of gravitation is

not only a demonstration that God can, if he pleases, put into bodies powers and ways of operation above what can be derived from our idea of body, or can be explained by what we know of matter, but also an unquestionable and every where visible instance, that he has done so.

(Locke 1823, vol. 4: 467–8; see also, 461)

These claims imply that gravity is not a primary quality but rather one that is superadded to matter.
Citing this article:
Anstey, Peter. Natural philosophy. Locke, John (1632–1704), 2017, doi:10.4324/9780415249126-DA054-2. Routledge Encyclopedia of Philosophy, Taylor and Francis,
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