Educated as a monk, Thomas became a popular speaker in his early twenties. He traveled from town to town, explaining Christianity and defending its beliefs. Europeans were then rediscovering the teachings of Aristotle and other philosophers of ancient Greece, who believed life should be lived by reason, rather than by faith. Thomas argued that there was no conflict between Aristotle's ideas and the teachings of Jesus. In fact. he claimed a person's faith and power to reason should work together.
After years of preaching, Thomas wrote down his ideas in a book called The Heights of Theology. His book became one of the cornerstones of modern Catholicism.