The chapter is focused upon the reconstruction of Lukács's arguments against irrationalism. Lukács's explanation of irrationalism is mostly causal in the general sense that complex structures are caused and can be explained by other complex structures. In this sense a causal relationship can be discovered between capitalism and irrationalist philosophy. But if irrationalism is causally determined by societal structure, and other supra-rational factors, it is irrational to believe in irrationalism. Conversely, it is also true that accepting rationalism is rational. Th is is contrary to Popper's and Lukács's views alike. Against Popper's theory it implies that there are rational arguments for rationalism. In contrast to Lukács' theory it involves that there are not only causal factors, but reasons (such as evidences and the requirement of logical consistency) that support accepting rationalism. In the conclusion a detailed argument is presented in favor of the thesis that rationalism can be based rationally.