§67 The tasks of pure logic. First: the fixing of the pure categories of meaning, the pure categories of objects and their law-governed combinations

We must, first of all, lay down the more important concepts, in particular all the primitive concepts which ‘make possible’ the interconnected web of knowledge as seen objectively, and particularly the web of theory. We must also clarify these concepts scientifically. We are, in other words, concerned with the concepts which constitute the Idea of unified theory, or with the concepts which are connected with these through ideal laws. Into such a constitution second-order concepts, i.e. concepts of concepts and of other ideal unities, naturally enter. A given theory is a certain deductive combination of given propositions which are themselves certain sorts of combinations of given concepts. The Idea of the pertinent ‘form’ of the theory arises if we substitute variables for these given elements, whereby concepts of concepts and of other Ideas, replace straightforward concepts. Here belong the concepts: Concept, Proposition, Truth etc.