the difference between "understanding" and "reason" in kant's terminology

while kant presupposes the existence of science and ethic, he studies their boundaries and limits as well. for doing this, he applies two terms and expressions, i.e., “reason” and “understanding”. in this paper, we take a look at the definitions of those two concepts in kant’s terminology within the approach that discriminates their differences. at first, the placement of these two faculties in science territory will be studied and then by examining of kant’s ethical point of view, it will be concluded that in this approach, the functionality of reason appears in act and ethic domains, and pure reason is practical in its essence.