Socrates is revered for his shifting of Greek philosophical thought from the contemplation of the nature of the universe, which occupied the philosophers before him, to the examination of human life and its problems. He was the first to study ethics as a science-that is, to study morality in a systematic, consistent manner. Scholars have noted that the impact of Socrates on the development of Western culture and philosophy cannot be overstated, and some have suggested that his teachings influenced the development of Christianity. Yet the study of Socrates's philosophy is plagued by the "problem of Socrates": he wrote nothing. After his death, and perhaps before it, his followers began to record details of his life and thought, but these are arguably more interpretive in nature than they are biographical. Therefore, one of the greatest debates surrounding Socrates is that of the accuracy and validity of the Socratic sources, primarily the writings of Xenophon and Plato. Other critical issues include the interpretation of Socrates's ethical theses that virtue is knowledge, wrong-doing is involuntary, and that the care of the soul is the primary condition for living well; and of his controversial views regarding the treatment of enemies and retaliation. Socrates was born in 469 B.C. in Athens to a stonemason (some sources state that Socrates's father was a sculptor) named Sophroniscus and his spouse, a mid-wife. He was a student of a physicist, Archelaus, and was perhaps interested in the philosophy of Anaxagoras. He is believed to have lived on a small inheritance and on investments made through a wealthy friend. Socrates served in the army, fought in the Peloponnesian War, and married a woman named Xanthippe, who bore two or three sons, sources say. When Socrates was 70 years old, he was accused of "irreligion," or impiety, and of corrupting the youth of Athens. In 399 B.C. he was tried, convicted, and condemned to die by drinking hemlock. While Socrates did not leave any writings, his followers Xenophon and Plato both wrote extensively about Socrates's beliefs and experiences. Yet their respective accounts differ markedly. In addition to the records of Xenophon and Plato, Aristophanes ridiculed Socrates in one of his comedies, Clouds (423 B.C.), and Aristotle commented on the philosoph