Descartes who is the originator of Cartesian doubt, invokes a very high standard of knowledge by subjecting all his beliefs, ideas, senses, and thoughts to the method of doubt. By using the method of doubt, he tries to find beliefs that can truly serve as the foundation of knowledge. The beliefs that cannot be deceived and be immune from doubt are considered to be part of the true knowledge. He argued that knowledge gained from the senses or through senses sometimes proved to be deceptive in nature and his beliefs on this bases cannot meet his high standards of Knowledge. He also argues that our own reasoning is not unjust when its concluded from science but without taking great trouble to ascertain whether they are actually existent or not, it would contain some measure of certainty and an element of the indubitable. He makes an assumption that in order to know something, he has to know various scenarios incompatible with the basis of his own knowledge are false.
He concludes that we do not know anything on the basis of our senses alone and as stated in his meditation is to suspend judgement about any belief that is even slightly doubtful. By testing his beliefs by doubt, he establishes the understanding of knowledge in terms of Certainty.I believe Descartes high standards are reasonable as this provides us a method of understanding the world based on the use of reason and having certainty with no doubts as the means to attain true knowledge. Not being able to distinguish between truth and falsity of various scenarios, it’s not possible to distinguish between seeing the world and having an exceptional realistic dream of seeing the world. According to Descartes, Certainty is not a feeling but involves a type of rational insight and only claims that are ‘clear and distinct’ can be certain.
By testing Certainty by reason, Descartes thinks that certainty will establish truth, because what cannot be otherwise must be true.