thesis / antithesis / synthesis 
In the philosophy of Hegel, the inevitable transition of thought, by contradiction and reconciliation, from an initial conviction to its opposite and then to a new, higher conception that involves but transcends both of them. Thus, for example: 

Being / Non-being / Becoming, 

subjective / objective / absolute, or 

symbolic / classical / romantic.

Since he identified reality with thought, Hegel believed that the same triadic movement is to be found in nature, cultural progress, and history. 

Recommended Reading: Hegel's Science of Logic, tr. by A. V. Miller (Humanity, 1998) {at Amazon.com}; Quentin Lauer, Essays in Hegelian Dialectic (Fordham, 1977) {at Amazon.com}; and Hans-Georg Gadamer, Hegel's Dialectic, tr. by P. Christopher Smith (Yale, 1982) {at Amazon
