Undoubtedly, A Priori needs to be clarified if we are to understand the heart of Critique of Pure Reason; and Kant, precisely for this very reason, devoted a considerable part of Critique to explaining the epistemic status of A Priori, searching its origin, specifying its validity scope, and illustrating its instances. Although he, more or less, in both editions of Critique, put forward some characteristics intrinsic to A Priori (such as necessary, strictly universal, pure, clear, certain and independent of experience) since they have been also used in (pre)post-Kantian traditions, especially in a meaning different from what Kant meant, so they may simply bring about some confusions cause failing to appropriately grasp the heart of Critique. With reference to such confusions the authors make an attempt to shed light on this point in part (1). Then, in part (2-1), based on the text of Critique and its commentators’ views, authors proceed to show that to evade such confusions one should re-define necessary to “ what is emerged from the nature of the human mind” , strictly universal to “ applicable just in the realm of phenomenon” , pure to “ merely focused on the contribution of mind itself in collaboration with the objects themselves to form empirical knowledge” , clear to “ what the scope of searching for is limited to within ourselves not outside of it” and certain to “ what its scope is immutable – either regarding to its instances themselves or to their numbers” . In part (2-2), by scrutinizing the other characteristic (i. e. independent of experience), we shall show that this characteristic, besides of referring to mere structure, can refer to some kind of knowledge on which every possible experience is based; moreover, we shall determine the relation of above characteristic to pre(post)-Kantian traditions.