Arthur Schopenhauer

“ By one of those bold generalizations which occasionally mark a real advance in Science, Schopenhauer conceived this unifying principle, this underlying unity, to consist in something analogous to that will which self-consciousness reveals to us. Will is, according to him, the fundamental reality of the world, the thing-in-itself; and its objectivation is what is presented in phenomena. The struggle of the will to realize itself evolves the organism, which in its turn evolves intelligence as the servant of the will. ”

“ That Schopenhauer conceives life as an evil is a deduction, and possibly a mistaken deduction, from his metaphysical theory. Whether his scheme of things is correct or not—and it shares the common fate of all metaphysical systems in being unverifiable, and to that extent unprofitable—he will in the last resort have made good his claim to be read by his insight into the varied needs of human life. ”

“ Written so as to be intelligible enough in themselves, the tendency of many of them is towards the fundamental idea on which his system is based. It may therefore be convenient to summarize that idea in a couple of sentences; more especially as Schopenhauer sometimes writes as if his advice had been followed and his readers were acquainted with the whole of his work.
All philosophy is in some sense the endeavor to find a unifying principle, to discover the most general conception underlying the whole field of nature and of knowledge. ”