In ancient Greece, LITERACY and interest in the natural world was common in an expanding upper class that devoted much of its leisure time to debate. Popular topics for discussion were the reality, causes, and principles of thinking and being, better known as PHILOSOPHY. These debates considered the facts independent of the traditional religious dogmas of the day, and opened the door to examination of a wide range of new ideas. The writings of many of these early Greek philosophers, including Plato and Aristotle, have been luckily preserved. It has been said that all PHILOSOPHY after Plato was no more than footnotes to his work.