Marxism has developed into many different branches and schools of thought, though now there is no single definitive Marxist theory. Different Marxian schools place a greater emphasis on certain aspects of classical Marxism while rejecting or modifying other aspects. Many schools of thought have sought to combine Marxian concepts and non-Marxian concepts, which has then led to contradictory conclusions. However, lately there is movement toward the recognition that historical materialism and dialectical materialism remains the fundamental aspect of all Marxist schools of thought, which should result in more agreement between different schools.
The term "Marxism" was popularized by Karl Kautsky, who considered himself an "orthodox" Marxist during the dispute between the orthodox and revisionist followers of Marx. Kautsky's revisionist rival Eduard Bernstein also later adopted use of the term. Engels did not support the use of the term "Marxism" to describe either Marx's or his views. Engels claimed that the term was being abusively used as a rhetorical qualifier by those attempting to cast themselves as "real" followers of Marx while casting others in different terms, such as "Lassallians". In 1882, Engels claimed that Marx had criticized self-proclaimed "Marxist" Paul Lafargue, by saying that if Lafargue's views were considered "Marxist", then "one thing is certain and that is that I am not a Marxist".