Some Marxist schools of thought place greater emphasis on certain aspects of classical Marxism while rejecting or modifying other aspects. Some schools have sought to combine Marxian concepts and non-Marxian concepts which has then led to contradictory conclusions. It has been argued that there is a movement toward the recognition of historical and dialectical materialism as the fundamental conceptions of all Marxist schools of thought. This view is rejected by some post-Marxists such as Ernesto Laclau and Chantal Mouffe, who claim that history is not only determined by the mode of production, but also by consciousness and will.