Pierre Gassendi (1592–1655) was a Catholic priest who was highly influential in justifying empirical science to religious dogmatists. He studied at Digne and Aix and became professor of rhetoric at Digne when he was 21. After he received his doctorate in theology at Avignon and was ordained a priest, he became professor of philosophy at Aix. He also pursued astronomical research. His Exercitationes Paradoxicae Adversus Aristoteleos (1625) set out all that he thought was dubious and mistaken in Aristotle’s writings. His principle attack on Aristotle was against the possibility of certain knowledge in science. Gassendi argued against Aristotle (384–322 B.C.E.) in his claim that certainty was neither possible nor necessary in science. At the same time, he sought to defend atomism against Church doctrine. Gassendi developed what came to be known as a mitigated or moderate skepticism that supported the conclusions of scientific inquiry.