But how could we realize such genera? Are all these genera susceptible of division, or do they lie entire within each of the objects they comprehend? If so, how does this unity find itself? Unity exists therein as a genus, just as the whole exists within the plurality. Does unity exist only in the objects that participate therein? Not only in these objects, but also in itself. This point will be studied later. QUANTITY IS A SECONDARY GENUS, THEREFORE NOT A FIRST. 13. Now why should we not posit quantity among the primary genera? And why not also quality? Quantity is not one of the primary genera like those we have posited, because the primary genera coexist with essence (which is not the case with quantity). Indeed, movement is inseparable from essence; being its actualization and life. Stability is implied in being; while identity and difference are still more inseparable from essence; so that all these (categories) appear to us simultaneously. As to number (which is discrete quantity), it is something posterior. As to (mathematical) numbers, far more are they posterior both to these genera, and themselves; for the numbers follow each other; the second depends on the first, and so forth; the last are contained within the first. Number, therefore, cannot be posited among the primary genera. Indeed, it is permissible to doubt whether quantity may be posited as any kind of a genus. More even than number, extension (which is continuous quantity), shows the characteristics of compositeness, and of posteriority. Along with number, the line enters into the idea of extension. This would make two elements. Then comes surface, which makes three. If then it be from number that continuous dimension derives its quantitativeness, how could this dimension be a genus, when number is not? On the other hand, anteriority and posteriority exist in dimension as well as in numbers. But if both kinds of quantities have in common this, that they are quantities, it will be necessary to discover the nature of quantity. When this will have been found, we shall be able to make of it a secondary genus; but it could not rank with the primary genera. If, then, quantity be a genus without being a primary one, it will still remain for us to discover to which higher genus, whether primary or secondary, it should be subsumed. NUMBER AND DIMENSION DIFFER SO MUCH AS TO SUGGEST DIFFERENT CLASSIFICATION.