Metaphysics is the endeavour to obtain knowledge of the nature of things generally. In Chapter 4 we have seen that Kant argues that concepts applicable to objects generally are discovered by reflecting on the concepts required for connecting any given concepts into judgments. The categories are the basic concepts available for metaphysical thinking. They are the concepts required for referring any given concepts to objects. However, the categories by themselves do not enlarge our knowledge of objects generally; for they are discovered by reflecting on the concept of an object in general. Kant argues that metaphysics can enlarge our knowledge of objects generally only by informing us of the properties of them that enable knowledge to be acquired of them by the categories.1 It is by empirical judgments that knowledge of things is directly acquired. These are verified by finding connections among what are presented us by our senses. Whatever our senses present us with, we can find no connections among them without being aware of how they are connected in time. In Chapter 6, we have seen that Kant argues that concepts of temporal determinations are therefore the basic concepts available for metaphysical knowledge. Yet it is by imagination that we become conscious of the temporal determinations of objects that enable us to acquire knowledge of them by the categories. Metaphysics therefore cannot enlarge our knowledge of things generally without reckoning with conditions by which imagination is bound in uniting what our senses present us with. This poses the question how categorial principles that are synthetic can then be verified by metaphysics a priori. In order to throw light on this question, Kant refers us first to geometry. In Chapter 5, we have already attended to the explanation Kant offers in the Transcendental Aesthetic of how geometrical judgments are verified a priori. Later in the Critique he enlarges upon this account. It is to this that we must now give attention.