matter has no extension, for extension is inseparable from the form, and that therefore it is incorporeal. Yet Aristotle had already taught that it is not a body although it is corporeal: "(
Greek characters)" (Stob. Ecl., lib. i., c. 12, 5). In reality we think under pure matter only action, in the abstract, quite independent of the kind of action, thus pure causality itself; and as such it is not an object but a condition of experience, just like space and time. This is the reason why in the accompanying table of our pure a priori knowledge matter is able to take the place of causality, and therefore appears along with space and time as the third pure form, and therefore as dependent on our intellect.
This table contains all the fundamental truths which are rooted in our perceptive or intuitive knowledge a priori, expressed as first principles independent of each other. What is special, however, what forms the content of arithmetic and geometry, is not given here, nor yet what only results from the union and application of those formal principles of knowledge. This is the subject of the "Metaphysical First Principles of Natural Science" expounded by Kant, to which this table in some measure forms the propædutic and introduction, and with which it therefore stands in direct connection. In this table I have primarily had in view the very remarkable parallelism of those a priori principles of knowledge which form the framework of all experience, but specially also the fact that, as I have explained in § 4 of the first volume, matter (and also causality) is to be regarded as a combination, or if it is preferred, an amalgamation, of space and time. In agreement with this, we find that what geometry is for the pure perception or intuition of space, and arithmetic for that of time, Kant's phoronomy is for the pure perception or intuition of the two united. For matter is primarily that which is movable in space. The mathematical point cannot even be conceived as movable, as Aristotle has shown ("Physics," vi. 10). This philosopher also himself
