The latter interests historians of esotericism, psychologists, and some philosophers and spiritualists. He exchanged letters with scientists, philosophers, musicians and other intellectuals. Various philosophers and scientists have proposed possible theories. At the court of Jayavarman V lived philosophers, scholars, and artists. Pythagoras was one of the first Western philosophers to stress rationalist insight. Unlike many of the more agnostic Enlightenment philosophers, Rousseau affirmed the necessity of religion. Many existentialist philosophers, like Arthur Schopenhauer, espouse this view. Notable Jesuits include missionaries, educators, scientists, artists, philosophers, and Pope Francis. This is an active discipline pursued by both trained philosophers and scientists. A larger group of pagan philosophers and writers stand behind them. This proposal has received criticism from both philosophers and computer scientists. Naturalism can be found in Democritus, Hobbes, Hume and many other modern philosophers. Berkeley influenced many modern philosophers, especially David Hume. Epicurus's teachings were heavily influenced by those of earlier philosophers, particularly Democritus. Deleuze's studies of individual philosophers and artists are purposely heterodox.