Spinoza's doctrine of the eternity of the mind is often understood as the claim that the mind has a part that is eternal. I appeal to two principles that Spinoza takes to govern parthood and causation to raise a new problem for this reading. Spinoza takes the composition of one thing from many to require causal interaction among the many. Yet he also holds that eternal things cannot causally interact, without mediation, with things in duration. So the human mind, since (...) it is the idea of a body existing in duration, cannot have an eternal part. In order to solve this problem, I propose an aspectual reading of Spinoza's doctrine of the eternity of the mind: the mind itself is eternal, under one of its aspects. (shrink)