Abelard, Peter (1079-1142) French philosopher. One of the most influential medieval logicians and theologians. Around 1113, while teaching theology in Paris, Abelard fell in love with his student Heloise, whom he secretly married; he was condemned for heresy a few years later because of his nominalist views. He wrote Sic et Non.
Anaxagoras (c. 500-428 B.C.) Greek pre-Socratic philosopher who is said to have made Athens the center of philosophy and to have been Socrates' teacher; he rejected the four elements theory of Empedocles and posited instead an infinite number of unique particles of which all objects are composed.
Anaximander (c. 611-547 B.C.) Greek pre-Socratic thinker who believed the universal substance to be "the boundless" or "the indefinite," rather than something resembling familiar objects. Unlike Thales (his teacher) and Anaximenes, he did not believe that a single element underlies all things.
Anaximenes (6th century B.C.) One of the pre-Socratics and an associate of Anaximander. He agreed with Thales that one type of substance underlies the diversity of observable things. Anaximenes believed that air was that universal substance and that all things are made of air in different degrees of density.
Anselm, St. (1033-1109) Italian monk and Scholastic theologian who became archbishop of Canterbury. St. Anselm founded Scholasticism, integrated Aristotelian logic into theology, and believed that reason and revelation are compatible. He is most famous for his influential ontological argument for God's existence.
Aquinas, St. Thomas (1225-74) The greatest thinker of the Scholastic School. His ideas, in 1879, made the official Catholic philosophy. He incorporated Greek ideas into Christianity by showing Aristotle's thought to be compatible with church doctrine. In his system, reason and faith (revelation) form two separate but harmonious realms whose truths complement rather than oppose one another. He presented influential philosophical proofs for the existence of God. His works include Summa Theologica and On Being and Essence .
Aristotle (384-322 B.C.) Greek philosopher, scientist, logician, and student of many disciplines. Aristotle studied under Plato and became the tutor of Alexander the Great. In 335 he opened the Lyceum, a major philosophical and scientific school in Athens. Aristotle emphasized the observation of nature and analyzed all things in terms of "the four causes." In ethics, he stressed that virtue is a mean between extremes and that man's highest goal should be the use of his intellect. Most of Aristotle's works were lost to Christian civilization from the fifth through the twelfth centuries. Among his writings are Metaphysics , Politics , and Rhetoric .
Augustine of Hippo, St. (354-430) The greatest of the Latin church fathers and possibly the most influential Christian thinker after St. Paul. St. Augustine emphasized man's need for grace. His Confessions and The City of God were influential.
Averroes (1126-98) Spanish-born Arabian philosopher, lawyer, and physician whose detailed commentaries on Aristotle were influential for over 300 years. He emphasized the compatibility of faith and reason but believed philosophical knowledge to be derived from reason. The church condemned his views.
Avicenna (980-1037) Islamic medieval philosopher born in Persia. His Neoplatoist interpretation of Aristotle greatly influenced medieval philosophers, including St. Thomas Aquinas. Avicenna was also a physician; his writings on medicine were important for nearly 500 years.
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