Descartes’ Methodical Doubt and Cogito: A Philosophical Journey
1. Methodical Doubt
He had long warned that, in relation to customs, it is sometimes necessary to follow very uncertain opinions as if they were undeniable, as I noted above. But since he wanted to surrender only to the pursuit of truth, he felt that he needed to do the opposite and reject as absolutely false everything in which he could imagine the least doubt, to check if, after doing this, there would not be something in his belief that was wholly indubitable. Thus, considering that our senses sometimes mislead us, he decided to assume that there was nothing that would make it as we imagine. And since there are men who make mistakes in reasoning on matters related to the simplest matters of geometry and acting in paralogisms, judging him, like any other, was subject to error, he rejected as false all the reasons which had hitherto supported demonstrations. And finally, considering that even the thoughts we have when awake can assault us when we sleep, with none in such a condition being true, he resolved to pretend that everything hitherto achieved by his spirit was no more true than the illusions of his dreams.
2. Cogito Discovery
But immediately afterwards he noticed that, while he thus wished to think that everything was false, it was absolutely necessary that he, who thought, was something. And realizing that this truth: I think, therefore I am, was so firm and so sure that all the most extravagant suppositions of the skeptics were not able to make it shake, he thought he could accept it without scruple as the first principle of philosophy that he was seeking.
3. Deduction: Thinking Substance
Later, looking hard at what he was, and seeing that he could pretend he had no body and there was no world or any place where he found it, but that, therefore, he could not pretend that he was not, but on the contrary, only after he thought about doubting the truth of other things, it followed very evidently and certainly that he was, while, if only he had ceased to think, though the rest of what he had imagined had been true, he had no reason to believe that he had been, he came to know from this that he was a substance whose nature or essence lies not only in thought and that such a substance, to exist, has no need of any place or depends on any material thing. So that this self, that is, the soul, by which he is what he is, is entirely distinct from the body, easier to learn it, and though the body were not, it would still be all that is.
4. The Criteria of Truth and Certainty
Examining these issues, reflecting in general on all that is required to affirm that a statement is true and certain, therefore, just identified as one that met such a condition, he thought he should also know what this certainty was. And when he realized that nothing in I think, therefore I am, was sure that he spoke the truth, unless he saw very clearly that he must be thinking, he reasoned that he could accept the general rule that the things we conceive very clearly and distinctly are all true, yet there are only some difficulties in properly identifying what are those we think differently.