In addition, he considers the generally excepted view that our senses dependably report the absolute nature of reality. Like authority though, Descartes discards the senses as a source of truth because of the "Dream Argument" or the belief that based on the senses there is no definite way of proving that you are dreaming or that you are awake. Therefore, it is possible that everything we believe is false, making the senses an unreliable source. Upon establishing this, Descartes doubts the existence of a physical or external world. Despite that, he has an idea of things in the world, he has no definitive way of knowing if they exist beyond his own mind. .
Another foundation that he tries to confirm is mathematics. But he soon realizes math's truth isn't completely reliable because of the "Demon Hypothesis", which acknowledges the possibility of an all powerful, malicious being that is deceiving him about everything, including mathematics. As a result, Descartes ponders the possibility that he has no way of being completely positive about anything, even existence. It is only after some deliberation that he comes to the conclusion that it is impossible to be incorrect about everything because he has doubt, and to posses doubt, there must be a doubter. Hence, he doubts, therefore he exists. With the assurance of his existence, he presents a deeper question of what he actually is. Descartes knows that he is not just a body based on his doubt of the senses. Despite the fact that he feels he is not a body, he does believe he has properties, such as doubt, that make him a substance. From this he concludes that his is an immaterial substance and that his essential property is self-consciousness because you can have no real proof of yourself except through your own thoughts or consciousness. Descartes articulates this belief in the statement, "I"m aware that I"m aware." .
Although he cannot yet be sure of the existence of anything external to or outside of his mind, the certainty of his own thoughts cannot be doubted.
