"It is best," some reader will say, "not to concern yourself with what cannot be known." But is it possible? In his very beautiful poem, _The Ancient Sage_, Tennyson said: Thou canst not prove the Nameless, O my son, Nor canst thou prove the world thou movest in, Thou canst not prove that thou art body alone, Thou canst not prove that thou art spirit alone, Nor canst thou prove that thou art both in one: Nor canst thou prove thou art immortal, no, Nor yet that thou art mortal--nay, my son, Thou canst not prove that I, who speak with thee, Am not thyself in converse with thyself, For nothing worthy proving can be proven, Nor yet disproven: wherefore thou be wise, Cleave ever to the sunnier side of doubt, Cling to Faith beyond the forms of Faith! Yes, perhaps, as the Sage says, "nothing worthy proving can be proven, nor yet disproven"; but can we restrain that instinct which urges man to wish to know, and above all to wish to know the things which may conduce to life, to eternal life? Eternal life, not eternal knowledge, as the Alexandrian gnostic said. For living is one thing and knowing is another; and, as we shall see, perhaps there is such an opposition between the two that we may say that everything vital is anti-rational, not merely irrational, and that everything rational is anti-vital. And this is the basis of the tragic sense of life. The defect of Descartes' _Discourse of Method_ lies not in the antecedent methodical doubt; not in his beginning by resolving to doubt everything, a merely intellectual device; but in his resolution to begin by emptying himself of himself, of Descartes, of the real man, the man of flesh and bone, the man who does not want to die, in order that he might be a mere thinker--that is, an abstraction. But the real man returned and thrust himself into the philosophy.