 These two pure forms of intuition—time and space—delivered, for Kant, the theories of arithmetic and Euclidean geometry respectively, and endowed them both with their a priori character. And they made possible the spatio-temporal manifold of intuitions (Anschauungen) which would then in turn, upon structuring by the exercise of concepts of the understanding (especially the concepts of substance and cause) make possible objective knowledge of things and events in the external world. 