The name libido can again be used to denote the manifestations of the power of Eros in contradistinction to the energy of the death instinct.[21] We must confess that it is more difficult for us to detect the latter, and to a great extent we can merely conjecture its existence as a background to Eros, also that it eludes us wherever it is not betrayed by a fusion with Eros. In sadism, where it bends the erotic aim to its own will and yet at the same time gratifies the sexual craving completely, we can obtain the clearest insight into its nature and its relation to Eros. But even where it shows itself without any sexual purpose, even in the blindest frenzy of destructiveness, one cannot ignore the fact that satisfaction of it is accompanied by an extraordinarily intense narcissistic enjoyment, due to the fulfilment it brings to the ego of its oldest omnipotence-wishes. The instinct of destruction, when tempered and harnessed (as it were, inhibited in its aim) and directed towards objects, is compelled to provide the ego with satisfaction of its needs and with power over nature. Since the assumption of its existence is based essentially on theoretical grounds, it must be confessed that it is not entirely proof against theoretical objections. But this is how things appear to us now in the present state of our knowledge; future research and reflection will undoubtedly bring further light which will decide the question. In all that follows I take up the standpoint that the tendency to aggression is an innate, independent, instinctual disposition in man, and I come back now to the statement that it constitutes the most powerful obstacle to culture. At one point in the course of this discussion the idea took possession of us that culture was a peculiar process passing over human life and we are still under the influence of this idea. We may add to this that the process proves to be in the service of Eros, which aims at binding together single human individuals, then families, then tribes, races, nations, into one great unity, that of humanity. Why this has to be done we do not know; it is simply the work of Eros. These masses of men must be bound to one another libidinally; necessity alone, the advantages of common work, would not hold them together. The natural instinct of aggressiveness in man, the hostility of each one against all and of all against each one, opposes this programme of civilization. This instinct of aggression is the derivative and main representative of the death instinct we have found alongside of Eros, sharing his rule over the earth. And now, it seems to me, the meaning of the evolution of culture is no longer a riddle to us. It must present to us the struggle between Eros and Death, between the instincts of life and the instincts of destruction, as it works itself out in the human species. This struggle is what all life essentially consists of and so the evolution of civilization