Descartes' theory of knowledge is that it is a conviction based on reason that is so strong that no feeling of doubt can change it. Descartes' epistemology is largely described in terms of being the contrast of doubt, according to Stanford University.
Furthermore, Descartes goes on to say that doubt is also in contrast to certainty. That as certainty continues to increase, doubt will decrease. Therefore, Descartes' theory of knowledge is that knowledge is an unwavering conviction with absolute certainty, as obtained through reason. This theory of knowledge is an "internalist" theory, as opposed to an externalist, which means that Descartes' believes that all humans with knowledge have access to evidence of that knowledge, suggests Stanford University.