Kant’s notion of synthetic a priori knowledge is rather technical and requires some technical explanation, in terms of what he means by what. It is therefore entirely necessary to define the relevant terminology from a Kantian perspective. Although Kant agrees with the commonly held definitions of some terms like a priori and empirical, it is important to note that he was the first philosopher to introduce the distinction between synthetic and analytic propositions. The purpose of Kant’s Critique of Pure Reason is to defend metaphysics from Hume’s outright exclusion of it from philosophy and Kant is of the opinion that the notion and possibility of synthetic a priori knowledge can do that (Gardner, 1999). Kant thinks that it is synthetic a priori knowledge that all metaphysical inquiry hopes to acquire and that the possibility of synthetic a priori knowledge is equivalent to the possibility of metaphysics (Gardner, 1999).
A priori knowledge is knowledge that is discoverable independently of experience by the operation of the mind or reason. Although for Kant and for Hume all knowledge is derived from experience, a priori knowledge is true in virtue of itself and needs no further experience to justify it. A priori knowledge is discoverable by merely thinking about the relations between ideas which themselves come from experience. In other words once we have, through experience, acquired the necessary ideas and concepts we can know certain truths about those concepts by merely thinking about them, and those truths need no further empirical evidence. A priori truths are true in virtue of the nature of the objects that they are about. For Kant, all a priori truths must be necessary or universal in order for them to be a priori (Gardner, 1999). Empirical or a posteri ...