Dialectic is an important Hegelian concept, even though it is only used a few times in Introduction to the Philosophy of History. It denotes a kind of progress-through-negation, in which Spirit destroys realizations of itself to rise again in a new and more fully realized form. This sense of dialectic is closely linked to the self-consciousness of Spirit. In knowing itself (the universal) as its own opposite (the subjective or particular), Spirit struggles against itself as it emerges in the world. The dialectic therefore helps to explain why rational history progresses through violent upheaval rather than through smooth transition.