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