  This much, however, does not explain how perception occurs. Aristotle claims that perception is best understood on the model of hylomorphic change generally: just as a house changes from blue to white when acted upon by the agency of a painter applying paint, so “perception comes about with &lt;an organ’s&gt; being changed and affected … for it seems to be a kind of alteration” (De Anima ii 5, 416b33–34). So in line with his general account of alteration, Aristotle treats perception as a case of interaction between two suitable agents: objects capable of acting and capacities capable of being affected. That the agents and patients must both be suitable is important, since we need to distinguish between two ways, e.g., an odor might affect something. By being placed in its vicinity, a clove of garlic might affect a block of tofu. The tofu might well come to take on the odor of the garlic. But we would not want to say that the tofu perceives the garlic. By contrast, when an animal is affected by the same clove, it perceives the odor. Since the garlic is the same in both cases, the difference in these cases must reside in the character of the object affected. When animals receive perceptual forms, perception results; when non-living entities are affected by what seem to be the same forms, only non-perceptual alteration occurs.