Aquinas: Faith Meets Aristotle

In the thirteenth century the complete works of Aristotle arrived in Europe through Arabic translations, and they caused a crisis. Here was a comprehensive, rigorous, entirely pagan account of nature, causation and the soul, and in places it flatly contradicted Christian doctrine. The University of Paris banned teaching it, more than once. Something had to be done with a body of thought that was too good to ignore and too dangerous to absorb.

Thomas Aquinas absorbed it. His answer to the crisis is a single principle with enormous consequences: faith and reason cannot genuinely conflict, because both come from the same source, and truth cannot contradict truth. So when they appear to clash, the conclusion is not that one must be abandoned. It is that somebody has misread something, and the job is to find out who.

Notice what this licenses. It makes serious investigation of the natural world safe rather than threatening, because no discovery can be a threat in principle. A result that seems to contradict doctrine is an invitation to check both the result and the reading of the doctrine. That stance, more than any particular argument he made, is why Aquinas matters outside theology.

The Five Ways are his best-known arguments and the most consistently misread. They are routinely taken as claims about what happened first: something must have started the universe. Aquinas held nothing of the sort. He thought reason alone cannot establish that the universe had a beginning in time at all, and said so.

What the arguments concern is a different kind of series. Take a hand moving a stick which moves a stone. Remove the hand and the whole thing stops instantly, not eventually, because every member of the series is only passing along a power it does not possess on its own. Aquinas argues a series like that cannot run backwards forever, since an infinite line of borrowers with no owner never explains the loan. Something must have the power in its own right. That is what the argument reaches for, and it is a claim about what sustains things now rather than about a first event.

He is also careful about what the arguments deliver. They reach what he says all people call God, and no further. Everything specifically Christian (the Trinity, the incarnation, grace) requires revelation. That division of labour is the whole architecture of the Summa, and it is why the accusation that his arguments prove too little slightly misses: he agreed.

His other lasting contribution is natural law. Moral principles, he holds, can be worked out by reason from human nature, without revelation. Reason grasps a first practical principle (good is to be pursued and evil avoided) in something like the way it grasps non-contradiction in logic. From natural inclinations toward self-preservation, family, society and knowledge, more specific precepts follow. This is why natural law arguments still appear in secular courts: they appeal to what human beings need in order to flourish, which anyone can assess.

The objection that has real force is that reading obligations off human nature has historically produced whatever the reader already believed. Aquinas insists many natural impulses must be governed rather than followed, so the framework is emphatically not natural means good. But the charge that nature is doing less work than it appears to has never fully gone away, and modern natural lawyers spend most of their energy on it.

One last thing worth knowing about him as a writer. Every article in the Summa states the strongest objections first, often better than their actual defenders managed, before giving his answer. Reading only the answers skips half the argument, and it is the half he was proudest of.