The division of human cognitive faculties into those based on reason and those based on experience belongs to the standard epistemological vocabulary. The controversy between empiricism and rationalism, which is one of the most important in epistemology, is organized around these categories. Both parties occur in their genetic and methodological versions. Within the former version, we have nativism (genetic rationalism) and genetic empiricism, but apriorism (methodological rationalism) and aposteriorism (methodological rationalism) are connected with the latter.¹ This chapter deals mainly with apriorism and aposteriorism, although their connections with the genetic issue will be also noted. The distinctions pointed out in the title are usually regarded as helpful in explaining how apriorism and empiricism are related. In particular, since both views appear in radical or moderate versions, it is important to see where the borderline between them should be drawn.