Schopenhauer assumes that our physical drives, on which depend our desires and wants, set the ground of knowledge and being. These drives are in the very source of our biological as well as our intellectual acts, i.e. at the essential content of man as a rational being. Moreover, not only men, but all beings, organic and inorganic get objectivity as a product of will. Will is the thing-in-itself which shows itself in the reality as a whole and in individual objects. (...) Schopenhauer argues that the thing-in-itself is will. In short, he will say that the “thing-in-itself” has an intelligible quality and that it is “will”. Kant associates the unknown character of the first cause with the inconclusive research of causes. This case, known as “the third antinomy”, takes the principle of causality to the impossibility of the existence of the first cause. Schopenhauer’s famous criticism of Kant relies on this point. Thus, he goes on to construct his own theory of causality and of space-time. Schopenhauer does this in the context of the sufficient reason principle. This study examines how this principle is handled by Schopenhauer in the famous fourfold root doctrine. According to Schopenhauer, there are four principles that govern four separate classes of objects. It is precisely this last principle which opens the way to Schopenhauer's metaphysics of will. His original interpretation appears at this point against traditional metaphysics. This study examines the theoretical roots of this philosopher's later, practical tendencies. (shrink)