Philosophy › Faith and reason
Thomas Aquinas
1225–1274· Philosopher· Reality, mind & God
Well documentedSolid records, texts or physical evidence.
Italian Dominican friar who built the most complete synthesis of Aristotle's philosophy and Christian theology, chiefly in his Summa Theologiae.
See it on the Philosophy map →The idea
The idea: faith and reason come from the same God, so they cannot truly conflict. Reason can prove that God exists; revelation adds truths, like the Trinity, that reason cannot reach. Trained by Albert the Great, Aquinas taught in Paris and Italy and wrote the Summa Theologiae (1265–1274), in which every article states objections, answers, then replies to each. He left it unfinished after a 1273 experience made his work seem 'like straw'. The main objection: his system leans on Aristotle's physics, since overturned.
Why it matters
His synthesis became the backbone of Catholic teaching, officially endorsed in 1879, and still shapes natural-law ethics, just-war theory and arguments about God.
Legacy and sources
His two Summas, Aristotle commentaries and some autograph manuscripts survive; early biographies and records of his 1323 canonization document his life.
Still debated
No one knows what happened in December 1273, when he stopped writing: a mystical vision, a stroke or exhaustion. He died months later, aged about 49.
Inside this (5)
Connections (8)
▸Aristotle was fused with Christian theology by Thomas AquinasWell documented
The connection
Aquinas adopted Aristotle's logic, physics and ethics and his account of the soul as the form of the body, calling him simply 'the Philosopher'. He argued that Aristotle's reasoning, properly understood, supports Christian belief, while correcting points like the world's eternity, which he said reason could neither prove nor disprove.
When and how
Paris and Italy, about 1256–1274; Aquinas wrote commentaries on about a dozen of Aristotle's works, using new translations from the Greek by William of Moerbeke.
How we know
His Aristotle commentaries survive, and the Summa Theologiae quotes 'the Philosopher' on nearly every page.
Debates and open questions
Whether Moerbeke translated at Aquinas's request is uncertain; scholars debate how much Aquinas reshaped Aristotle, for example by adding the creator God Aristotle lacked.
▸Natural law (the Stoics and Cicero) was developed by Thomas AquinasWell documented
The connection
Aquinas took the Stoic and Ciceronian idea of a moral law built into nature and set it in a Christian scheme: eternal law in God's mind, natural law as humans' rational share in it, and human law, valid only if it agrees with natural law. Its first principle: do good and avoid evil.
When and how
The 'Treatise on Law' in the Summa Theologiae (Part I–II, questions 90–97), written around 1270, drawing on Cicero, Roman jurists and Augustine.
How we know
Aquinas cites Cicero, Roman law and Augustine by name in the treatise, and repeats Augustine's line that an unjust law seems to be no law at all.
Debates and open questions
Philosophers still debate whether natural law can be known by reason alone, without belief in God, and how it applies to modern rights.
▸Augustine of Hippo was synthesized with Aristotle by Thomas AquinasWell documented
The connection
Augustine was the Western church's greatest authority, steeped in Plato; Aristotle was the newly translated master of logic and nature. Aquinas wove them together, keeping Augustine's teaching on grace, sin and God but explaining knowledge through Aristotle's senses-first account rather than Augustine's divine illumination.
When and how
Paris and Italy, 1250s–1274; Augustine is the Church Father Aquinas cites most often in the Summa Theologiae.
How we know
The Summa constantly pairs 'the Philosopher' with Augustine, often using Augustine for the 'on the contrary' authority that frames Aquinas's answer.
Debates and open questions
Franciscans such as Bonaventure felt Aquinas gave too much to Aristotle at Augustine's expense; how faithful he was to Augustine is still debated.
▸Avicenna (Ibn Sina) influenced Thomas AquinasWell documented
The connection
Avicenna's distinction between a thing's essence (what it is) and its existence (that it is) became central for Aquinas, who argued that only in God are essence and existence identical. Avicenna's argument from contingent and necessary being also shaped Aquinas's Third Way, and his theory of the soul informed Aquinas's psychology.
When and how
Avicenna's Metaphysics and On the Soul reached Latin in Toledo around 1150–1180; Aquinas used them in Paris from the 1250s, notably in On Being and Essence.
How we know
Aquinas cites Avicenna by name frequently, and his early treatise On Being and Essence (c. 1255) relies on him openly.
Debates and open questions
Scholars debate whether Aquinas's idea of existence as an act truly comes from Avicenna or is his own original turn.
▸Maimonides, Guide for the Perplexed influenced Thomas AquinasWell documented
The connection
Aquinas read the Guide in Latin and called its author 'Rabbi Moses'. He followed Maimonides in holding that reason cannot settle whether the world had a beginning, that much biblical language about God is figurative, and that God reveals some truths reason could reach for those without time to study. He rejected Maimonides' purely negative theology.
When and how
The Guide was translated into Latin around the 1240s, probably in Paris; Aquinas used it from his Sentences commentary in the 1250s onward.
How we know
Aquinas cites 'Rabbi Moses' by name repeatedly, including in the Summa's discussions of divine names and creation.
Debates and open questions
Scholars debate how much of Aquinas's method for reconciling faith and reason came from Maimonides rather than from Avicenna or Christian sources.
▸Thomas Aquinas formulated Aquinas' Five WaysWell documented
The connection
Aquinas rejected Anselm's proof from the mere idea of God, arguing that we must reason from effects we can observe. In one compact article of the Summa Theologiae he set out five arguments, from motion, causation, contingency, degrees of perfection and purposeful order, each ending at something 'everyone calls God'.
When and how
Rome, at the Dominican house of Santa Sabina, about 1266–1268, as he began the Summa Theologiae for beginning theology students.
How we know
The text survives as Summa Theologiae Part I, question 2, article 3; the first article of the same question explicitly rejects Anselm's approach.
Debates and open questions
Scholars debate why he wrote them so briefly; he gave fuller versions elsewhere, as in the Summa contra Gentiles, and may have meant a summary for students.
▸Thomas Aquinas marked the high point of Scholasticism and the recovery of AristotleMostly agreed
The connection
Aquinas used the scholastic method at full scale: each article of his Summa poses a question, lists objections, cites an authority, gives his answer and replies to every objection. His integration of Aristotle with Christian doctrine became, for many, the model of what scholastic philosophy could achieve.
When and how
University of Paris and Dominican schools in Italy, 1252–1274; he was a leading master of the 13th century, alongside Bonaventure and his teacher Albert the Great.
How sure are we?
His works became standard teaching in Dominican schools from about 1300, and Pope Leo XIII recommended them for all Catholic education in 1879.
Debates and open questions
Calling him the peak reflects later Catholic emphasis; in his day he was controversial, and some of his views were caught up in the 1277 Paris condemnation.
▸William of Ockham challenged the realism of Thomas AquinasMostly agreed
The connection
Aquinas held a moderate realism: real shared natures exist in things, and the mind abstracts them. Ockham denied that any shared nature exists outside the mind; only individuals are real, and universals are just mental signs. He also doubted reason could prove much about God, separating theology from philosophy more sharply than Aquinas did.
When and how
Oxford and London, about 1317–1324, in Ockham's commentary on Peter Lombard's Sentences and in his Summa Logicae.
How sure are we?
Ockham's writings state and reject realist positions directly; historians trace the late-medieval split between the 'old way' of Aquinas and Scotus and Ockham's 'modern way'.
Debates and open questions
His main target on universals was often John Duns Scotus rather than Aquinas; how directly he engaged Aquinas himself is debated.