The will may be defined, not as a definite, separate power, but as the self-conscious impulse to action resulting from excitation. Any other definition is inconsistent with the theory of evolution, according to which that individuation which is the first condition of the struggle for existence, is nevertheless but the expression of all previously existing oppositions. To make of the will or of the impulse to self-preservation anything separate and individual, is as childish as to personify death. The individual is totality as unity. Darwinism teaches us, not that the world together with man has been created according to any teleological principle, but that it has developed by virtue of motion. The human being moves by virtue of reciprocal action and reaction with the world. Yet only by virtue of his unity as feeling does he think and will. Individuality is that which stamps all our activity with the mark of the ego, which causes us to recognize every impulse that moves in us as our impulse, to call all our willing ours. The psychical, the summation of functions to which we give this name, reaches consummation in the clarification of feeling to consciousness, in which the desire of an action or of abstinence from an action appears to us as our will. As thought is based on perception, so will is based on impulse; and since thought and will appear as the two highest opposites of feeling, and this, according to our definition, springs from sensation by way of perception, the will, including action and abstinence from action, arises out of the general sensitivity. The progress of science authorizes the expectation that the close relation of sensitivity to simple reaction will one day be discovered. The conceptions of teleology are groundless. The so-called "ends" of nature have the peculiarity that they are according to the means. It does not rain in order that there may be vegetation, but vegetation exists because it is conditioned by the rain. Only with thinking man, in his struggle for existence, arises the concept of ends; man has not attained to civilization by help of a friend; rather has he wrung civilization from nature as an enemy; compelled by it to the exertion of his whole strength, and growing in cunning by exercise, he has learned to use the weaknesses of his foe to his own advantage. To want he owes the greatest things that he has accomplished. By way of labor alone can victory over nature be achieved and salvation won.