That "I am" seems a sort of epitome of the humanism, not to say of the pathos of the humanism of the time. Man had lost everything but his own self, his lacking, longing, always seeking self. Montaigne put the situation plainly when he said in so many words, that portrayal of self was the beginning and the end alike of physics, the science of outer reality, and metaphysics the science of all reality. Man had been left with his mere self, robbed of beliefs and traditions, and abandoned by everything but his doubts and the empty companionship which these afforded, but to that, an unshaped thing with an undefined activity, real only for what it did not have, he clung tenaciously and often enthusiastically. And Descartes spoke for him: _Knowing that I have nothing, I am_.
But in this self that was real only because always lacking, always doubting, Descartes found a priceless treasure. Every one is familiar with the principle of Christian theology, that the conviction of sin is a real promise because the actual beginning of salvation, and every one has some appreciation of this principle. It is a principle, too, that no priest ever made or could ever unmake, belonging as it does to the very nature of conscious creatures. In like manner, [p.185] then, Descartes recognized in the consciousness of doubt, or say of intellectual error, the real promise, because the actual beginning or even the very presence of veracity in knowledge. The doubter, conscious of error as he must be, was never without and never by any possibility could be without a sense for truth, an idea of veracity. Doubting all things he must yet believe in truth. Plato said centuries before that mere opinion, however false, was nevertheless always in love with true knowledge, and this Platonic love Descartes found in the doubter's conviction of error. In Plato's spirit Descartes insisted that doubt was a constant yearning for truth, a persistent faith in it. Doubt was informed with truth, with the idea of truth, very much as one has the "idea" of a thing that one cannot master. Man might be a doubter of all things, then, but in spite of his doubt he must believe in the reality of things, not exactly in the individual reality of each and every thing, but in reality in and among all things. For him, doubting and self-conscious, there must dwell in the world a realizing nature or power, an agent of perfect veracity, checking any experience from being altogether deceptive. And, for the present, to narrow our attention to a single phase of the doubter's natural idea of veracity, as Descartes reasoned about it, truth and everything that goes with truth, perfection and absoluteness in all its phases, could not be solely human if to doubt was human. They must, in consequence, be divine. So God, a spirit of truth and righteousness, was real, as real as the real self of always doubting but ever truth-loving man. _Dubito, cogito; ergo sum: etiam_ [p.186] _Deus est. I doubt, I think; as thinker and doubter I am: and what is more, God, veracity incarnate, is also_.