This simple infinity, or the absolute notion, may be called the simple essence of life, the soul of the world, the universal blood, whose omnipresence is neither disturbed, nor interrupted by any difference, but rather is itself every difference, as also their supersession; it pulsates within itself but does not move, inwardly vibrates, yet is at rest. It is self-identical, for the differences are tautological; they are differences that are none. This self-identical essence is therefore related only to itself; 'to itself' implies relationship to an 'other,' and the relation-to-self is rather a self-sundering; or, in other words, that very self-identicalness is an inner difference. These sundered moments are thus in and for themselves, each an opposite--of an other; thus in each moment the 'other' is at the same time expressed; or each is not the opposite of an 'other' but only a pure opposite; and so each is therefore in its own self the opposite of itself.
Georg Wilhelm Friedrich Hegel, “The Phenomenology of Spirit” (1807).