his thoughts may be vain.  If man is the creature of a wicked and cunning being, the light of reason may be only an ignis fatuus kindled by a malicious and mocking spirit.  Here is a soul plunged in the lowest abysses of doubt; but it is a manly soul which seeks in doubt a trial for truth, and not a comfortable pillow on which slothfully to repose.  How does Descartes upraise himself?  By a thought known to every one, and which was already found in St. Augustine:  “Cogito, ergo sum.  I think, therefore I am.”  Deceive me who will; if I am deceived, I exist.  Here is a certainty protected from all assault:  I am.  But what a poor certainty is this!  What does it avail me to have rescued my existence from the abysses of universal doubt, if above the deep waters which have swallowed up all belief floats only this naked and mortifying truth:  I am; but I exist only perhaps to be the sport of errors without end.  The first step therefore taken by the philosopher would be a fruitless one if it were not followed by a second.  An eye is open, and says:  I see; but it must have a warrant that the light by which it sees is not a fantastic brightness.  No, replies Descartes; reason sees a true light; and this is how he proves it:  I am, I know myself; that is certain.  I know myself as a limited and imperfect being; that again is certain.  I conceive then infinity and perfection; that is not less certain; for I should not have the idea of a limit if I did not conceive of infinity, and the word imperfect would have no meaning for me, if I could not imagine perfection, of which imperfection is but the negation.  Starting from this point, the philosopher proves by a series of reasonings that the conception of perfection by our minds demonstrates the real existence of that perfection:  God is.  He adds, that the existence of God is more certain than the most certain of all the theorems of geometry.  You will observe, Gentlemen, that the man who speaks in this way is one of the greatest geometricians that ever lived.  He has found God, he has found the light.  Reason does not deceive, when it is faithful to its own laws:  the senses do not deceive, when they are exercised according to the rules of the understanding.  Error is a malady; it is not the radical condition of our nature; it is not without limits and without remedy, for the final cause of our being is God, that is to say truth and goodness.

     From everlasting God was true,
     For ever good and just will be,

says one of our old psalms.  Faith in the veracity of God—­such is the ground of the assurance of believers; such is also the foundation on which has been raised the greatest of modern philosophies.  Without the knowledge of God and faith in his goodness, man remains plunged in irremediable doubt, possessing only this single, poor, and frightful certainty:  I am; and I exist perhaps only to be eternally deceived.