Having thus made myself sure of these maxims, and having set them apart together with the verities of faith, I judged that for the rest of my opinions I might set freely to work to divest myself of them. For nine years, therefore, I went up and down the world a spectator rather than an actor. These nine years slipped away before I had begun to seek for the foundations of any philosophy more certain, nor perhaps should I have dared to undertake the quest had it not been put about that I had already succeeded. _IV.--"I THINK, THEREFORE I AM"_ I had long since remarked that in matters of conduct it is necessary sometimes to follow opinions known to be uncertain, as if they were not subject to doubt; but, because now I was desirous to devote myself to the search after truth, I considered that I must do just the contrary, and reject as absolutely false everything concerning which I could imagine the least doubt to exist. Thus, because our senses sometimes deceive us I would suppose that nothing is such as they make us to imagine it; and because I was as likely to err as another in reasoning, I rejected as false all the reasons which I had formerly accepted as demonstrative; and finally, considering that all the thoughts we have when awake can come to us also when we sleep without any of them being true, I resolved to feign that everything which had ever entered into my mind was no more truth than the illusion of my dreams. But I observed that, while I was thus resolved to feign that everything was false, I who thought must of necessity be somewhat; and remarking this truth--"_I think, therefore I am_"--was so firm and so assured that all the most extravagant suppositions of the sceptics were unable to shake it, I judged that I could unhesitatingly accept it as the first principle of the philosophy I was seeking. I could feign that there was no world, I could not feign that I did not exist. And I judged that I might take it as a general rule that the things which we conceive very clearly and very distinctly are all true, and that the only difficulty lies in the way of discerning which those things are that we conceive distinctly.