We have to distinguish two classes of instincts, one of which, the sexual instincts or Eros, is by far the more conspicuous and accessible to study.... The second class of instincts was not so easy to point to; in the end we came to recognize sadism as its representative. On the basis of theoretical considerations, supported by biology, we put forward the hypothesis of a death instinct, the task of which is to lead organic life back into the inanimate state; on the other hand, we supposed that Eros ... aims at complicating life and at the same time, of course, at preserving it. Acting in this way, both the instincts ... would be endeavouring to re-establish a state of things that was disturbed by the emergence of life. The emergence of life would thus be the cause of the continuance of life and also at the same time of the striving towards death; and life itself would be a conflict and compromise between these two trends.

Quote