1. ONTOLOGY is the first part of Wolff’s metaphysics. Ontology treats of what are now called categories, or those fundamental conceptions which are applied to every object, and must therefore at the outset be investigated. Aristotle had already furnished a table of categories, but he had derived them wholly empirically. It is not much better with the ontology of Wolff; it is laid out like a philosophical dictionary. At its head he places the principle of contradiction, viz.: it is not possible for any thing to be, and at the same time not to be. The conception of the possible at once follows from this principle. That is possible which contains no contradiction. That is necessary, the opposite of which contradicts itself, and that is accidental, the opposite of which is possible. Every thing which is possible is a thing, though only an imaginary one; that which neither is, nor is possible, is nothing. When many things together compose a thing, this is a whole, and the individual things comprehended by it are its parts. The greatness of a thing consists in the multitude of its parts. If A contains that by which we can understand the being of B, then that in A by which B becomes understood is the ground of B, and the whole A which contains the ground of B is its cause. That which contains the ground of its properties is the essence of a thing. Space is the arrangement of things which exist conjointly. Place is the determinate way in which a thing exists in conjunction with others. Movement is change of place. Time is the arrangement of that which exists successively, etc.