That the logical development of the categories of thought is the same as the historical evolution of life—­and vice versa—­establishes for Hegel the identity of thought and reality.  In the history of philosophy, the discrepancy between thought and reality has often been emphasized.  There are those who insist that reality is too vast and too deep for man with his limited vision to penetrate; others, again, who set only certain bounds to man’s understanding, reality consisting, they hold, of knowable and unknowable parts; and others still who see in the very shifts and changes of philosophic and scientific opinion the delusion of reason and the illusiveness of reality.  The history of thought certainly does present an array of conflicting views concerning the limits of human reason.  But all the contradictions and conflicts of thought prove to Hegel the sovereignty of reason.  The conflicts of reason are its own necessary processes and expressions.  Its dialectic instability is instability that is peculiar to all reality.  Both thought and reality manifest one nature and one process.  Hence reason with its “dynamic” categories can comprehend the “fluent” reality, because it is flesh of its flesh and bone of its bone.  Hegel’s bold and oft quoted words “What is rational is real; and what is real is rational,” pithily express his whole doctrine.  The nature of rationality and the nature of reality are, for Hegel, one and the same spiritual process, the organic process of triumphing over and conquering conflicts and contradictions.  Where reality conforms to this process it is rational (that which does not conform to it is not reality at all, but has, like an amputated leg, mere contingent existence); the logical formula of this process is but an abstract account of what reality is in its essence.

The equation of the real and the rational, or the discovery of one significant process underlying both life and reason, led Hegel to proclaim a new kind of logic, so well characterized by Professor Royce as the “logic of passion.”  To repeat what has been said above, this means that categories are related to one another as historical epochs, as religious processes, as social and moral institutions, nay, as human passions, wills, and deeds are related to one another.  Mutual conflict and contradiction appear as their sole constant factor amid all their variable conditions.  The introduction of contradiction into logical concepts as their sine qua non meant indeed a revolutionary departure from traditional logic.  Prior to Hegel, logical reasoning was reasoning in accordance with the law of contradiction, i. e., with the assumption that nothing can have at the same time and at the same place contradictory and inconsistent qualities or elements.  For Hegel, on the contrary, contradiction is the very moving principle of the world, the pulse of its life. Alle Dinge sind an sich selbst widersprechend, as he drastically says.