I distinguish two senses in which organisms are mechanically inexplicable for Kant. Mechanical inexplicability in the first sense is shared with artefacts, and consists in their exhibiting regularities irreducible to the regularities of matter. Mechanical inexplicability in the second sense is peculiar to organisms, consisting in the reciprocal causal dependence of an organism's parts. This distinction corresponds to two strands of thought in Aristotle, one supporting a teleological conception of organisms, the other supporting a conception of organisms as natural. Recognizing (...) this distinction helps us to see how a teleological conception of organisms is compatible with recent advances in biology. (shrink)