Rationalism holds that reason rather than experience is the basis of knowledge. Two main rationalist philosophers discussed are Plato and Descartes.
Plato believed that knowledge comes from innate ideas and recollection of forms from our pre-earthly existence. He believed that reason allows understanding of transcendent truths. Descartes developed a method of intuition and deduction, believing that some truths about reality can be intuitively known with certainty and further knowledge deduced from intuitions.
Descartes presented rules in his Discourse on Method to ensure the intellect can grasp all that can be known through orderly and certain processes of reason alone.