 Many philosophers maintain there is a significant difference between primary and secondary qualities but disagree about its foundation. It may be plausible that we perceive things as having a small number of basic qualities which are determinates or degrees of the following: size, figure, extension, duration, motion, position, color, taste, odor, sound, heat, coldness, and tactual qualities such as hardness, softness, roughness and smoothness. The first six (to which solidity and number are sometimes added) are called “primary”; roughly speaking, they are said to be real objective properties of objects and to be distinctly known. The remaining, called “secondary”, are said to be in some way—metaphysically, epistemically, linguistically—derivative, less than fully real, or otherwise metaphysically feeble; or misleading, subjective, ambiguous, or otherwise not perspicuous. The lists map the extension of the division and the doctrine explains its basis.