Reason and Faith

In the 12th and 13th centuries, a slow avalanche of Aristotle's works was arriving in Latin Europe. Most of Aristotle had been lost to the Christian West for centuries, preserved and commented on in the Islamic world by thinkers like Avicenna and Averroes, and slowly translated into Latin as European and Islamic scholars came into contact through Spain and Sicily.

This was intellectually exhilarating and theologically dangerous at the same time. Aristotle was the greatest philosopher most medieval Europeans had ever encountered, and he was not a Christian. He wrote about ethics, politics, physics, and metaphysics without mentioning God as Christians understood him. Some of his conclusions openly contradicted Christian doctrine: he seemed to hold that the world was eternal (not created), that God did not know individual human beings, and that the soul might not be immortal in the way Christians thought.

The Church's response was cautious. In 1210, the teaching of Aristotle's natural philosophy was banned at the University of Paris. The ban was repeated in 1215 and 1231. The worry was that Aristotle's authority would displace Scripture, and that his pagan premises would corrupt Christian thinking.

By the time Aquinas arrived at Paris in the 1240s, the ban had effectively collapsed. Everyone was reading Aristotle. The question was not whether to use him but how. Some of Aquinas's contemporaries, often called "Latin Averroists," argued that Aristotle should be read on his own terms, even where he disagreed with Christianity, and that there could be truths of reason that contradicted truths of faith. Others, more conservative, argued that Aristotle was simply too pagan to be trusted.

Aquinas charts a third path. He argues that there is only one truth, and that when Aristotle and Christian revelation appear to conflict, one of them has been misread. The project of the Summa, in a certain sense, is the long execution of that argument.

Aquinas's basic position on the relationship between philosophy and theology can be stated simply. God reveals truth in two ways: through the book of nature (which we read with reason) and through the book of Scripture (which we read with faith). Both books have the same author. If we read them correctly, they cannot ultimately disagree.

Reason and revelation are not rivals. They cover somewhat different territory and serve different purposes, but they work together. Reason can get us a long way. We can prove the existence of God, Aquinas thinks, by rational argument from what we observe in the world (he is famous for his "five ways" of doing this). We can work out much of ethics by reflecting on human nature. We can understand a great deal about what kind of creatures we are and what it would mean for us to live well.

But there are truths we cannot reach by reason alone. The doctrine of the Trinity, the Incarnation, the specific details of salvation history: these are truths of faith, known to us only because God has revealed them. Reason cannot prove them, but it can show that they are not contradictory, and it can defend them against objections.

This is why Aquinas does not experience Aristotle as a threat. Aristotle worked out an enormous amount about the natural world and about human life just by using his reason. Everything he got right is a part of the truth God made accessible through natural inquiry. Where Aristotle got things wrong or missed things, revelation can correct him. What matters is that reason and revelation are on the same side.

For our purposes, the most important application of this picture is in ethics. Aquinas will argue that much of ethics is accessible to reason alone, without revelation. You do not need to be a Christian to know that murder is wrong or that we owe our parents honor. These conclusions follow from careful reflection on what human beings are and what our good consists in. This is the central claim of natural law theory, which we will examine in detail in the next two lecture pages.

Recall Aristotle's basic picture from Unit 1. Every living thing has a telos, a natural purpose. The good for a thing is to fulfill its telos well. The human telos is the activity of the soul in accordance with reason. Therefore the human good is eudaimonia: the activity of the soul in accordance with reason, performed well, across a complete life.

Aquinas accepts this framework almost entirely. He agrees that humans have a nature, that nature has a telos, and that the good for us is the fulfillment of that telos. What he adds is an explanation of where the telos comes from. Human nature, on Aquinas's view, is not just there in the furniture of the universe. It is the kind of nature God chose to create when God made human beings. Our telos is the end God designed us for.

This has two consequences that will matter for the rest of the unit.

First, moral order is not a brute fact. It is the expression of a rational will. When Aquinas talks about the "eternal law," he means something like the plan or pattern in the divine mind, the way the creator thinks about creation. Every natural thing, including us, is governed by this law in the sense that every natural thing has the nature God gave it. For things without reason, this governance is automatic: rocks fall, fire burns, plants grow. For rational creatures like us, the governance works differently. We can recognize the rational order of things and freely choose to conform to it. That conformity is what Aquinas calls our participation in the eternal law.

Second, Aristotle's purely this-worldly account of eudaimonia needs to be extended. Aristotle thought the highest form of eudaimonia was the contemplative life, the life of the philosopher. Aquinas thinks this is right as far as it goes, but he adds that the full human end cannot be achieved in this life at all. Our deepest happiness, the complete flourishing we were made for, is the vision of God in the next life. This is not something reason alone can reach, but revelation tells us it is possible. Ethics in this life, for Aquinas, is partly about living well here and partly about preparing for the end we were made for.

You do not have to accept Aquinas's theological framework to follow his arguments. Most of the ethics in our reading can stand on its own. But it helps to notice when the framework is doing work, and this telos-as-divine-design move is one of the places where it shows up most clearly.

The Aristotelian inheritance runs all through Aquinas's ethics. A short list of what he takes over:

Teleology. Everything is directed toward some end. The good for a thing is the fulfillment of its end. This is the structural bedrock of both thinkers' ethics.

Virtue. Aquinas agrees with Aristotle that moral virtues are stable dispositions of character, acquired by habituation, that enable us to live well. He accepts the four classical virtues (prudence, justice, fortitude, temperance) and devotes enormous space to analyzing each one in the Second Part of the Second Part of the Summa. He adds three "theological" virtues (faith, hope, love) that are gifts of divine grace rather than products of habituation, but the fundamental Aristotelian framework remains intact.

Practical reason. Aquinas, like Aristotle, holds that ethical knowledge is practical rather than theoretical, and that the virtuous person is someone who reliably perceives what the situation calls for. The technical term prudentia in Aquinas corresponds closely to Aristotle's phronesis.

The idea that ethics starts from human nature. For both thinkers, the way to know what we should do is to understand what we are. Ethics is not read off a list of commandments; it is worked out by reasoning about what kind of creature we are and what our good consists in.

What Aquinas adds to all this is the theological frame that gives it a source and an ultimate direction. The result is a genuinely new synthesis, one that shapes Catholic moral thought for centuries afterward and still anchors a significant current in contemporary ethics.