Enneads VI.2: The Categories of Plotinos
Sixth Ennead, Book Two
1. After having discussed the doctrine of the ten categories (of Aristotle), and spoken of the (Stoics) who reduce all things to a single genus, and then distribute them in four species, we must still set forth our own opinion on the subject, striving however to conform ourselves to the doctrine of Plato.
Plotinos Is Forced to Demonstration of His Divergence from Plato
If it were our opinion that essence was one, we would not need to study whether there was one single genus for all things, whether all genera could not be reduced to a single one; whether there were principles; whether the genera were at the same time principles; or whether all principles are genera, without saying conversely that all genera are principles; or, if we must distinguish between them, say that some principles are simultaneously genera, or some genera are principles, or, finally, whether all principles be genera without the genera being principles, and conversely. But, since we do not acknowledge that essence is one, the reasons for which were advanced by Plato and other philosophers, we find ourselves forced to treat all these questions, and first to explain why we recognize genera of essences, and what number we decide on.