Final answer:
Rene Descartes sought certainty in knowledge through innate, clear and distinct ideas, using systematic doubt and rational introspection to question previously held beliefs. Plato also valued the intellect for understanding essential truths, influencing epistemology and ethics.
Step-by-step explanation:
Rene Descartes, a seminal figure in modern philosophy, doubted the veracity of the truths he had accepted in his youth. His skepticism led him to question all previously held beliefs, laying the groundwork for his famous dictum, "I think, therefore I am." Descartes sought certainty and believed that such certainty could only be found in clear and distinct ideas, which constitute the foundation of true knowledge. These ideas, according to Descartes, are innate and indubitable, such as knowledge of the self, God, and the world. The pursuit of certainty in knowledge drove Descartes to adopt a method of systematic doubt, famously including the hypothesis of an evil demon capable of deceiving us about the external world. Unlike the empirical approach which relies on the senses, Descartes' method emphasized rational introspection.
Similarly, other philosophers like Plato also underscored the importance of the intellect over the senses in grasping essential truths. For Plato, real knowledge or 'Forms' can only be apprehended through abstract reasoning, transcending the imperfections of the sensory world. This philosophy has had profound implications for various fields, including epistemology, metaphysics, and even politics and ethics.