  Under this pressure from Philonous, Hylas retreats (perhaps a bit quickly) from naïve realism to a more “philosophical” position. He first tries to make use of the primary/secondary quality distinction associated with mechanism and, again, locatable in the thought of Descartes and Locke. Thus, Hylas allows that color, taste, etc. may be mind-dependent (secondary) qualities, but contends that figure, solidity, motion and rest (the primary qualities) exist in mind-independent material bodies. The mechanist picture behind this proposal is that bodies are composed of particles with size, shape, motion/rest, and perhaps solidity, and that our sensory ideas arise from the action of such particles on our sense organs and, ultimately, on our minds. Berkeley opposes this sort of mechanism throughout his writings, believing that it engenders skepticism by dictating that bodies are utterly unlike our sensory experience of them. Here Philonous has a two-pronged reply: (1) The same sorts of relativity arguments that were made against secondary qualities can be made against primary ones. (2) We cannot abstract the primary qualities (e.g. shape) from secondary ones (e.g.  color), and thus we cannot conceive of mechanist material bodies which are extended but not (in themselves)  colored.[11]