I understand Locke's definitions of Primary Qualities as being mind-independent and residing in the world, and Secondary Qualities as being mind-dependent and reliant on us. But did he provide a actual list/ definition for deciding what's what? I believe he described 'roundness' as a primary quality. I can see how physical shape/dimensions are objective primary qualities, but when you get to concepts like 'roundness' it feels more subjective and secondary. Is there a clear rule to delineate the difference, or is it just judgement in some cases?

  • See John Locke : The Limits of Human Understanding : "Locke offers an account of physical objects based in the mechanical philosophy and the corpuscular hypothesis.Atoms have properties. They are extended, they are solid, they have a particular shape and they are in motion or rest. They combine together to produce the familiar stuff and physical objects, the gold and the wood, the horses and violets, the tables and chairs of our world. 1/2 May 15, 2018 at 13:41
  • These familiar things also have properties. They are extended, solid, have a particular shape and are in motion and at rest. In addition to these properties that they share with the atoms that compose them, they have other properties such as colors, smells, tastes that they get by standing in relation to perceivers. The distinction between these two kinds of properties goes back to the Greek atomists. It is articulated by Galileo and Descartes as well as Locke’s mentor Robert Boyle." 2/2 May 15, 2018 at 13:41

1 Answer 1


See An Essay Concerning Human Understanding : Book II, Chapter VIII by John Locke.

  1. Primary qualities of bodies.

Qualities thus considered in bodies are,

First, such as are utterly inseparable from the body, in what state soever it be ; and such as in all the alterations and changes it suffers, all the force can be used upon it, it constantly keeps ; and such as sense constantly finds in every particle of matter which has bulk enough to be perceived ; and the mind finds inseparable from every particle of matter, though less than to make itself singly be perceived by our senses : v.g. Take a grain of wheat, divide it into two parts ; each part has still solidity, extension, figure, and mobility : divide it again, and it retains still the same qualities ; and so divide it on, till the parts become insensible ; they must retain still each of them all those qualities. [...] These I call original or primary qualities of body, which I think we may observe to produce simple ideas in us, viz. solidity, extension, figure, motion or rest, and number.

  1. Secondary qualities of bodies.

Secondly, such qualities which in truth are nothing in the objects themselves but power to produce various sensations in us by their primary qualities, i.e. by the bulk, figure, texture, and motion of their insensible parts, as colours, sounds, tastes, &c. These I call secondary qualities.

  • I understand the general distinction Locke makes, but it seems precise definitions of the difference is debatable, and that was my point. I gave 'roundness' as an example because it seems to me a bit more subjective/secondary than an object's precise shape. Further down the Stanford article you linked to is 'There has been considerable scholarly debate concerning the details of Locke’s account of the distinction. Among the issues are which qualities Locke assigns to each of the two categories... Another issue is what the criterion is for putting a quality in one list rather than another.'
    – Simon K
    May 16, 2018 at 9:56
  • So to restate my question; can anyone give some more precise examples of the disagreements over certain qualities being primary or secondary?
    – Simon K
    May 16, 2018 at 9:59
  • @SimonK - agreed: it is debatable and it was debated. Locke's primary qualities list is : "solidity, extension, figure, motion or rest, and number" contrasted to secondary ones : "colours, sounds, tastes". Thus "roundness" must be figure. May 16, 2018 at 10:00
  • The criteria is : "what is utterly inseparable from the body" vs "what is mind-dependent". May 16, 2018 at 10:01

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