But Peter Olivi thinks it suffers from two fatal weaknesses.8 The first is that, whatever it means for the so-called “species” of green to turn up in your eye, the presence of that species in the eye cannot be identical with, or even give rise to, a perception in your soul. Immaterial things can certainly influence physical things, as when your soul commands your hand to reach out to take an olive out of a bowl, but the reverse is not the case. Bodies cannot affect anything incorporeal. That’s the first problem with the species theory, one that would, of course, only impress someone who shares
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