Plato (428–347 B.C.E.) and Aristotle (384–322 B.C.E.), the two most famous Greek philosophers, have had far-reaching influence on Western thought. While neither is best known for his psychological ideas, both have had impact on Western conceptions of the mind. Plato believed that the truth lay in abstract concepts, or forms, that could be grasped through reason alone. The data we get from our senses is impermanent and therefore illusory. The notion of an inborn mental ability to grasp concepts and categories is consistent with modern cognitive psychology and neuroscience, although the dismissal of “sense data” is not. Aristotle was much more enamored of the natural world and believed knowledge to come from systematic logical reasoning about our observations of nature. He maintained that the capacity for logical reasoning is innate but the content of our knowledge can only be grasped through our senses. In this way, Aristotle anticipated the foundations of modern science.