1. Primary: (extension) and Secondary qualities (sounds, feels, tastes smells, and colors)
2. Descartes: There is no reason to assume that sensations (secondary qualities: odors, tastes, sounds, colors and feels) resemble their causes. What's "in" here, "in" your mind, need not be anything like what triggered or produced it "out there."
3. Sensory perception as a trigger for response best suited to Darwinian survival: The evolutionary explanation of sense impressions.
4.The "look" and "feel" of the world to you or me and the way the world is apart from being seen, felt, or touched.
5. Descartes: Through reason we can "abstract" everything the mind contributes to our view of the external world; remove, peel away, the odor, smell, taste, color, feel, of a thing and be left with its primary qualities. And what are those? Descartes: these are spatially extended things("res extensa")
6. Locke (1632-1704): Secondary qualities: "which in truth are nothing in the objects themselves, but powers to produce various sensations in us by their primary qualities, i.e., by the bulk, figure, texture, and motion of their insensible parts, as colors, sounds, tastes, etc."Primary qualities: "original qualities of body which I think we may observe to produce simple ideas in us, viz. solidity, extension, figure, motion or rest, and number."