When I say that Descartes consecrated doubt, you must remember that it was that sort of doubt which Goethe has called “the active scepticism, whose whole aim is to conquer itself;"[70] and not that other sort which is born of flippancy and ignorance, and whose aim is only to perpetuate itself, as an excuse for idleness and indifference.  But it is impossible to define what is meant by scientific doubt better than in Descartes’ own words.  After describing the gradual progress of his negative criticism, he tells us:—­

“For all that, I did not imitate the sceptics, who doubt only for doubting’s sake, and pretend to be always undecided; on the contrary, my whole intention was to arrive at certainty, and to dig away the drift and the sand until I reached the rock or the clay beneath.”

And further, since no man of common sense, when he pulls down his house for the purpose of rebuilding it, fails to provide himself with some shelter while the work is in progress; so, before demolishing the spacious, if not commodious, mansion of his old beliefs, Descartes thought it wise to equip himself with what he calls “une morale par provision,” by which he resolved to govern his practical life until such time as he should be better instructed.  The laws of this “provisional self-government” are embodied in four maxims, of which one binds our philosopher to submit himself to the laws and religion in which he was brought up; another, to act, on all those occasions which call for action, promptly and according to the best of his judgment, and to abide, without repining, by the result:  a third rule is to seek happiness in limiting his desires, rather than in attempting to satisfy them; while the last is to make the search after truth the business of his life.

Thus prepared to go on living while he doubted, Descartes proceeded to face his doubts like a man.  One thing was clear to him, he would not lie to himself—­would, under no penalties, say, “I am sure” of that of which he was not sure; but would go on digging and delving until he came to the solid adamant; or, at worst, made sure there was no adamant.  As the record of his progress tells us, he was obliged to confess that life is full of delusions; that authority may err; that testimony may be false or mistaken; that reason lands us in endless fallacies; that memory is often as little trustworthy as hope; that the evidence of the very senses may be misunderstood; that dreams are real as long as they last, and that what we call reality may be a long and restless dream.  Nay, it is conceivable that some powerful and malicious being may find his pleasure in deluding us, and in making us believe the thing which is not, every moment of our lives.  What, then, is certain?  What even, if such a being exists, is beyond the reach of his powers of delusion?  Why, the fact that the thought, the present consciousness, exists.  Our thoughts may be delusive, but they cannot be fictitious.  As thoughts, they are real and existent, and the cleverest deceiver cannot make them otherwise.