s the detailed history of his doubts. He has told us how
he found that he could, plausibly enough, doubt of everything except
his own existence. He pushed his scepticism to the verge of
self-annihilation. There he stopped: there in self, there in his
consciousness, he found at last an irresistible fact, an irreversible
certainty. Firm ground was discovered. He could doubt the existence
of the external world, and treat it as a phantasm. He could doubt the
existence of God, and treat the belief as a superstition. But of the
existence of his own thinking, doubting mind, no sort of doubt was
possible. He, the doubter, existed if nothing else existed. The
existence that was revealed to him in his own consciousness, was the
primary fact, the first indubitable certainty. Hence his famous _Cogito
ergo Sum_: I think, therefore I am." (_Lewes's Bio. Hist. Phil._)

Proceeding from the certainty of his existence, Des Cartes endeavors
to rind other equally certain tacts, and for that purpose presents
the following doctrine and rules for our guidance:--The basis of all
certitude is consciousness, consciousness is the sole foundation of
absolute certainty, whatever it distinctly proclaims must be true.
The process is, therefore, rendered clear and simple: examine your
consciousness--each distinct reply will be a fact.

He tells us further that all clear ideas are true--that whatever is
clearly and distinctly conceived is true--and in these lie the vitality
of his system, the cause of the truth or error of his thinkings.

The following are the rules he gave us for the detection and separation
of true ideas from false, (_i.e._, imperfect or complex):--

"1. Never to accept anything as true but what is evidently so; to admit
nothing but what so clearly and distinctly presents itself as true, that
there can be no reason to doubt it.

"2. To divide every question into as many separate parts as possible,
that each part being more easily conceived, the whole may be more
intelligible.

"3. To conduct the examination with order, beginning by that of objects
the most simple, and therefore the easiest to be known, and ascending
little by little up to knowledge of the most complex.

"4. To make such exact calculations, and such circumspections as to be
confident that nothing essential has been omitted. Consciousness being
the basis of all certitude, everything of which you are clearly and
distinctly conscious must be true: everything which