The difference between the a priori and the a posteriori is a central issue in Kant's philosophy. It is an important question, not only because we should keep the a priori and the a posteriori apart, but also because the a priori is the logical or conceptual condition for the a posteriori. The forms of intuition, for example, are a priori, and they are ">a priori because they are the conditions for observation. All observation requires some form of condition, and as conditions, these forms are conceptually (not temporally) prior to observation.