Joseph Dietzgen, a tanner by trade, was self-taught and developed his theory of dialectical materialism independently of Karl Marx. In this book he argues that thinking is a process involving two opposing aspects—generalization and specialization—and all thought is therefore a dialectical process. Knowledge is limited, truth is relative, and the only absolute is existence itself. This cornerstone of socialist philosophy lays the foundation for a nondogmatic, flexible, nonsectarian yet principled socialist politics.