Complex sentence: It is a rejection of positivism within economics which defends an a priori epistemology and defines the science of "praxeology" upon a foundation of methodological individualism and laws of apodictic certainty.
Split into simpler sentences: It is a rejection of positivism within economics. It defends an a priori epistemology and defines the science of "praxeology" upon a foundation of methodological individualism and laws of apodictic certainty.