  A thing’s essence may not be absolutely equivalent to its nature for Spinoza, since a thing such as a square circle has a nature but cannot exist (Ip11) and one might interpret Spinoza as holding that anything which has an essence might exist (IId2). Still, the two terms might be taken interchangeably here because Spinoza is only describing existents. If this assumption is correct, then perhaps Spinoza’s reasoning runs like this: