The treatise "On the Fourfold Root of the Principle of Sufficient Reason" constitutes in its basic form the doctoral thesis of Arthur Schopenhauer, which the philosopher himself later elaborated. As he himself admits, this work became the foundation of his entire philosophical system. The main theme of the work is the so-called "principle of the sufficient reason (or ground)", according to which all things in the world have some sufficient cause that justifies their existence in an entirely comprehensible manner. Thus, the principle of the sufficient reason becomes the basis of all sciences. More specifically, the "fourfold root" is examined, that is, the form and function of this principle in the four basic categories into which the philosopher divides things: natural phenomena, concepts, mathematical theorems, objects of the will.