Plotinos: Complete Works, v. 3 In Chronological Order,...

1. Very ancient philosophers have investigated the number and kinds of essences. Some said there was but one;296 others, that there was a limited number of them; others still, an infinite number. Besides, those who recognized but a single (essence) have advanced opinions very different, as is also the case with those who recognized a limited or unlimited number of essences. As the opinions of these philosophers have been sufficiently examined by their successors, we shall not busy ourselves therewith. We shall study the doctrine of those who, after having examined the opinions of their predecessors, decided on determinate numbers (of essences); admitting neither a single essence, because they recognized that there was a multiplicity even in the intelligibles; nor an infinite number of essences, because such an infinity could not exist, and would render all science impossible; but who, classifying the essences whose number is limited, and seeing that these classifications could not be considered elements, looked on them as "kinds." Of these, some (the Peripatetic Aristotelians) proposed ten, while others proposed a lesser number (the Stoics taught four), or a greater number (the Pythagorean "oppositions," for instance). As to the kinds, there is also difference of opinions: some looked upon the kinds as principle (Plotinos himself); while others (Aristotle) held that they formed classes.