It should be clearly understood that thought is nothing but the organic function of the brain; and it has to obey the same laws in regard to exertion and repose as any other organic function. The brain can be ruined by overstrain, just like the eyes. As the function of the stomach is to digest, so it is that of the brain to think. The notion of a soul,—as something elementary and immaterial, merely lodging in the brain and needing nothing at all for the performance of its essential function, which consists in always and unweariedly thinking—has undoubtedly driven many people to foolish practices, leading to a deadening of the intellectual powers; Frederick the Great, even, once tried to form the habit of doing without sleep altogether. It would be well if professors of philosophy refrained from giving currency to a notion which is attended by practical results of a pernicious character; but then this is just what professorial philosophy does, in its old-womanish endeavor to keep on good terms with the catechism. A man should accustom himself to view his intellectual capacities in no other light than that of physiological functions, and to manage them accordingly—nursing or exercising them as the case may be; remembering that every kind of physical suffering, malady or disorder, in whatever part of the body it occurs, has its effect upon the mind. The best advice that I know on this subject is given by Cabanis in his Rapports du physique et du moral de l'homme.[32]
32 ([a]return])
[ Translator's Note. The work to which Schopenhauer here refers is a series of essays by Cabanis, a French philosopher (1757-1808), treating of mental and moral phenomena on a physiological basis. In his later days, Cabanis completely abandoned his materialistic standpoint.]
Through neglect of this rule, many men of genius and great scholars have become weak-minded and childish, or even gone quite mad, as they grew old. To take no other instances, there can be no doubt that the celebrated English poets of the early part of this century, Scott, Wordsworth, Southey, became intellectually dull and incapable towards the end of their days, nay, soon after passing their sixtieth year; and that their imbecility can be traced to the fact that, at that period of life, they were all led on? by the promise of high pay, to treat literature as a trade and to write for money. This seduced them into an unnatural abuse of their intellectual powers; and a man who puts his Pegasus into harness, and urges on his Muse with the whip, will have to pay a penalty similar to that which is exacted by the abuse of other kinds of power.
And even in the case of Kant, I suspect that the second childhood of his last four years was due to overwork in later life, and after he had succeeded in becoming a famous man.
Every month of the year has its own peculiar and direct influence upon health and bodily condition generally; nay, even upon the state of the mind. It is an influence dependent upon the weather.