Dialectics

In Hegel's philosophy, change occurs through the tension between an initial thesis and its contradiction, or antithesis. Reconciliation of this contradiction leads to synthesis, a higher conception that involves but transcends both thesis and antithesis. For Hegel, this movement from thesis, to antithesis, to synthesis is characteristic not only of thought, but also of nature, cultural progress, and history. Marx and Engels differed from Hegel in that they saw dialectics as a product of human labor changing the world. Hegel believed that dialectics could only be understood through pure reason, whereas Engels and Marx believed it must be understood through thought and practice--through the the practical struggle to overcome contradictions.

Reference

http://mingo.info-science.uiowa.edu/~stevens/critped/terms.htm

Hegel

Marx

Engels