is a form of philosophical scepticism
associated with the writings and methodology of René Descartes
Cartesian doubt is methodological. Its purpose is to use doubt as a route to certain knowledge by finding those things which could not be doubted. The fallibility of sense data in particular is a subject of Cartesian doubt.
René Descartes, the originator of Cartesian doubt, automatically put all beliefs, ideas, thoughts, and matter in doubt. He showed that his grounds, or reasoning, for any knowledge could just as well be false. Sensory experience, the primary node of knowledge, is often erroneous and therefore must be doubted. For instance, what one is seeing may very well be a hallucination. There is nothing that proves it cannot be. In short, if there is any way a belief can be disproved, then its grounds are insufficient. From this, Descartes proposed two arguments, the dream and the devil.
Descartes, knowing that the context of our dreams - while possibly unbelievable - is often lifelike, hypothesized that humans can only believe that they are awake. There are no sufficient grounds by which to distinguish a dream experience from a waking experience. For instance, Subject A sits at her computer, typing this article. Just as much evidence exists to indicate that her composing this article is reality as there is to demonstrate the opposite. Descartes conceded that we live in a world that can create such ideas as dreams. However, by the end of The Meditations
, he concludes that we can distinguish dream from reality at least in retrospect.
Descartes reasoned that our very own experience may very well be controlled by an "evil demon" of sorts. This demon, or genius, is powerful enough to control anybody. He could have created a superficial world that we may think we live in.
Descartes believed that doubt can be erased by studying the "first person." This heralded the term "cogito ergo sum
" – "I think, therefore I am".