Thomas Aquinas

Key ideas

Aquinas argued that faith and reason are complementary, and that much can be known by reason alone. His Five Ways are arguments from features of the world, such as change, causation and contingency, to a first cause. The argument from contingency is a cornerstone of the why there is something rather than nothing debate.

His ethics combines Aristotle's virtues with a theory of natural law: moral principles that can be known by reason from human nature. In discussing killing in self-defence, he noted that one act can have two effects, one intended and one merely foreseen. This became the doctrine of double effect, which still shapes debates about the trolley problem, medicine and war.

Life, briefly

Aquinas was born into a noble family near Aquino in southern Italy. When he joined the new Dominican order, his family kidnapped him and held him for about a year to try to change his mind. He studied under Albert the Great and taught in Paris and Italy.

Late in 1273 he stopped writing, reportedly saying that what he had written seemed like straw compared with what he had seen. He died the following year, leaving the Summa Theologiae unfinished.

Major works

• Summa Theologiae
• Summa contra Gentiles
• On Being and Essence
• commentaries on Aristotle

Schools of thought

Virtue ethics

Further reading

• EncyclopediaStanford Encyclopedia of Philosophy: Thomas Aquinas
• WikipediaThomas Aquinas