Medieval Philosophy

by Peter S. Adamson

The theologian is like the optician who doesn’t understand geometry, who we might say takes it as “a matter of faith” that parallel lines won’t meet in the end. Likewise, the theologian operates with perfectly certain principles, without himself understanding why they are certain.

In a set of famous arguments, often called the “five ways,” Aquinas describes five routes to establishing that God does in fact exist (ST Q2 a3 resp). These are some of the most thoroughly discussed arguments in the history of philosophy, and if all that discussion has shown anything, it is that the arguments need a lot of help if they are to be made watertight and convincing. For this reason I tend to sympathize with readers who see the five ways in the context of

theology, as Aquinas understands theology. Remember that philosophy offers various services to the theologian. These include proving certain preliminary points, which could certainly include the existence of God. But philosophy can also help us to understand things we already accept on the basis of faith, and you can be sure that these would most definitely include the existence of God. So it may be better to think of the five ways as offering the theologians a set of rational approaches for thinking about God, even if they are also intended to work as proofs.

what [Aquinas] is saying is like this: although there are several objections to the assumption that God exists, which should be taken seriously, we Christians firmly hold…that God is existent. Now, granted that this is true, as we believe it is, let us then try with the help of arguments found in the philosophical tradition to show how the human mind may be led to an understanding of this truth.6

Most thirteenth-century thinkers followed Augustine, who held that it is simply incoherent to argue that God doesn’t

exist. A typical Augustinian argument to this effect was that God is truth, and it is self-defeating to deny that there is truth: to do so you’d have to say that it is true that there is no truth (Q2 a1 obj 3). This sort of reasoning had been used by Anselm, who was, of course, responsible for an even more famous attempt to show that God’s existence simply cannot be denied. This was his ontological argument, which Aquinas interprets as trying to establish that God’s existence is self-evident (Q2 a1 obj 2). For Aquinas the argument fails, because it concludes from what must be the case in our minds to what must be the case in external reality. Though Aquinas does put his finger on a feature of the argument that makes people uncomfortable, I don’t think it is a good objection. After all, the whole point of the ontological argument is to move from our idea of God to God’s real existence. Aquinas simply rules this out as an illegal kind of inference. This amounts to stipulating that the ontological argument doesn’t work rather than pinpointing where exactly the flaw in Anselm’s reasoning might be. If God’s existence is not self-evident, how should it be established? On the basis of sense perception, of course, since it is on the basis of the visible created world that the invisible must be known.7 Each of the five ways duly takes its departure from a feature of the world of sense experience. Take the first of the ways. It argues that every motion depends on some cause which mo...

never begin. Thus, there is a first mover which, Aquinas blithely adds, “everyone understands to be God.” You see what I mean: the argument has more holes than the plot of a movie about the invention of Swiss cheese. How do we know that something can’t move itself, as when I get up from the sofa to fetch a drink from the kitchen? And why isn’t it possible to have a chain of moved causes, each of which is moved by the previous cause, into infinity? Or take the third of the five ways, which is probably the most mystifying. Here Aquinas asks whether it could be the case that all things are merely possible or contingent. No, because a contingent thing can fail to exist. So, if all things are contingent, then at some point everything would have failed to exist. But that is absurd, because if everything had been non-existent in the past, then nothing would exist now. It follows that not everything is contingent. Instead, there must be a necessary being, and, again, this is what everyone understands to be God.8 The argument looks almost painfully bad, especially the bit where he infers that if each thing could fail to exist, then at some point all things must fail to exist. Aquinas may...

have us turn to Avicenna, whose own more elaborate proof of the necessary existent is lurking in the background. A similar game can be played with the first way. In that case we might seek answers in Aristotle, who is the inspiration for Aquinas’ argument, or elsewhere in Aquinas, by looking to his theory of action to see why absolute self-motion is impossible.10 Of course, we might also use our own ingenuity to improve the argument; plenty of Thomas’ admirers have done so. But a more sensible reaction might be to assume that the student is familiar with these types of argument from studying their Aristotle and Avicenna and is just being reminded of several philosophical approaches to God that ca...

We’ve seen how prevalent it was to suppose that the human soul consists of numerous forms, and that many philosophers of the time made human knowledge depend on “illumination” from God. On both issues Aquinas would depart from the consensus.2 He’s having none of these plural forms you’ll find in other theories of soul; or rather, he’s having only one of them. The functions of human life proceed from the single form that he identifies as the rational human soul. To some extent this is just good Aristotelianism, at least as far as Aquinas is concerned. Every substance has a single substantial form and each human soul plays that role for the human who possesses it.

But my rational soul provides me with all the features and capacities that are essential to me as a human being. Proponents of form pluralism found it incredible that just one form could produce such a wide variety of effects.

Aquinas thinks this pluralist objection confuses the need for many forms with the need for many powers. Just one form can bestow many capacities on a substance, so long as the substance has many different parts for exercising those capacities

Like a reliable pizzeria, Aquinas’ theory delivers what it promises, by securing the unity of the soul where form pluralism would give us only an aggregate or “heap” (DQS 11 resp). What we loosely refer to as lower “souls,” responsible for things like digestion and sensation, are mere capacities within the single form that is the rational soul. Thus far he is endorsing the position that Kilwardby will condemn at Oxford. Aquinas wants to go further still, though. He insists that the soul is the only substantial form to be found in each human. It is predicated directly of prime matter, rather than coming on top of lower-level constituents that are themselves substances (DQS 9 resp). Thus,

there would be no actual elements, like fire and earth, in the human body, because, if there were, the substantial forms of fire and earth would be present. And that would undermine the unity of the human substance. While the claim is a bold one, it isn’t quite as crazy as it may first seem. Though Aquinas does not want to admit that there are any further full-blown substances within each person, he is happy to admit that the human has parts like blood, bones, heart, and brain.

If the soul were a second substance in the bodily substance, some third intermediary principle would be needed to bind these two substances together (DQS resp 6), whereas it was supposed to be the soul itself that unifies the human. Powerful though these considerations are, Aquinas’ view faced more stiff opposition than the hero in a zombie movie. Bonaventure’s student John Pecham was just one figure who insisted on form pluralism, condemning the Thomistic doctrine in 1284, a decade after Aquinas died. Another posthumous attack came from William de le Mare,

whose Correction of Brother Thomas argued that a plurality of substantial forms could still constitute a unified soul if they worked together in a coordinated fashion.

Given that the Catholic Church is well known for insisting that a fully human life begins at conception, it’s intriguing to find that the Church’s most canonical thinker doesn’t think anything of the sort. Instead, Aquinas believes that the presence of a rational soul requires the presence of organs that can carry out its functions. Since this is lacking at early stages of fetal development, only the lower nutritive or plant-like functions are present at first. They are succeeded by the functions of the sensory and motive powers and finally by the advent of the distinctively human rational soul. The lower functions also have a different source than the powers of reason. They are brought out of the material provided by the parents, whereas the rational soul can be given only by God and so is created directly in the embryo at some point during gestation. With the arrival of each new kind of soul the previous form is destroyed or “discarded,” to be replaced with a new single and unified form, which, however, retains the powers available to the previous forms that were in the embryo

The generation of a fetus is in some sense a continuous process, and at the very least Aquinas will want to say that the early embryo has the potential to become the human that will actually develop some weeks later. So there’s some prospect of harmonizing the two positions or at least minimizing the tension between them.4

He thinks the soul’s condition after death is unnatural to it and that the soul will be unable to exercise many of its powers in that condition. In a way that’s good news, since it gives him a sound basis for insisting on the need for eventual bodily resurrection, which is, of course, standard Christian doctrine. But he still needs to persuade us that the soul can somehow avoid vanishing between the moment of bodily death and the future time when it gets its body back.5 Here he points to Aristotle’s claim that intellectual thought is a purely immaterial process requiring no bodily organ. Were it seated in an organ, the mind’s processes

would be particularized and thus unable to engage in general, universal thinking (DQS 14 resp, ST 1 Q75 a2). And if the mind can engage in its distinctive operation without using the body, then it can survive the death of the body.6 But Aquinas seems to be trying to have his pizza and eat it too. On the one hand, my mind must act without my body in order to think universally. On the other hand, my mind is only my mind because it is a power of my soul, and my soul is only my soul because it is tied to my particular body (DQS 2 resp). This is a point on which Aquinas really needs to insist. Unlike some of the radical Aristotelians who were active in Paris around the same time, he absolutely rejects the proposal of Averroes that there is only one intellect for all of humankind, befitting the universality of intellective thinking. Instead, the mind borrows the individuality of the soul, which is in turn individual because it is the form of one individual body. This explains an obvious fact which Aquinas never tires of invoking against Averroes: when a person thinks, it is that person, and not anyone else, who is thinking

It’s traditional to contrast that illumination theory, which has its roots in Augustine, with the hard-nosed Aristotelian empiricism of Aquinas. But Aquinas agrees with the illumination theory to some extent. He too thinks something further is needed in order to transform the particular images of sensation, imagination, and memory into the universal ideas present in our minds. This something extra is the agent intellect. Again he here takes issue with many of his predecessors, especially thinkers of the Islamic world like Avicenna, who postulated a single agent intellect that activates thinking in the individual minds of particular humans. No, says Aquinas: it is true that some principle is needed to confer actual intelligibility and universality on our representations of things, but that principle is within the human soul (DQS 15 resp, ST 1 Q79 a3). Each of us is created by God with our own agent intellect, a “natural light” that we carry within us and that we can use to illuminate the images of things we have encountered in the world around us.

From a more sympathetic point of view, though, Aquinas may seem to be striking a balance between the illumination theory and a more extreme form of empiricism. He thinks that humans are born with everything they need to think abstract, universal thoughts, yet denies that such thoughts require nothing more than the particular images we glean through sensation.

What we haven’t yet learned is this: why is it so important to have knowledge anyway? It’s so important, Aquinas would say, that it is one reason we are given bodies in the first place.

Augustine’s view on this matter was a strict one: though pagans may on occasion seem virtuous, their virtue is in fact false. For their actions, no matter how admirable they may seem, are not directed towards the true goodness of the Christian God.

Yet one could admit the possibility of pagan virtue while avoiding Pelagianism. It is one thing to say that everyone will, if left to

their own devices, sin at some point or other, another to say that no one can ever be truly virtuous on any occasion without God’s help. So we need to seek a deeper explanation of the medieval denial of pagan virtue.

There’s a parallel here to the Augustinian theory of knowledge. We’ve seen how medieval proponents of the “illumination” theory argued, again following Augustine, that God must be somehow involved every time a human achieves genuine understanding. Likewise, on the ethical front, divine help was needed if humans were to be capable of genuine goodness. It was often said that virtue is “infused” into the human by God, much as the mind is illuminated with knowledge by the divine light. A good example is Philip the Chancellor, whose ethical views we discussed in Chapter 26. He shows his Augustinian credentials by suggesting that all real virtues come from God. Natural “virtue” such as was possessed by the pagans would not be virtue in the true sense of the word.3 Philip also calls this natural kind of moral excellence “political” virtue because it is expressed in our this-worldly life and in our dealings

with other people, rather than having to do with our relationship to God.

This position had the advantage of agreeing with Augustine and Peter Lombard, two of the pillars that supported early thirteenth-century scholasticism. But it had disadvantages too. For one thing, it seems frankly implausible. Are we really to believe that Socrates was not showing real courage when he unflinchingly drank the hemlock, that not a single decision reached by pagan judges had ever been truly just? For another thing, there was Aristotle. As we also saw in Chapter 26, it took a while for his Nicomachean Ethics to become available in a complete Latin version. Once it did, the medievals were confronted with Aristotle’s lengthy and sophisticated explanation of how virtue is acquired through moral education, which leads to the cultivation of good habits.4 How could his readers continue insisting that true virtue must be infused, and never acquired through natural means?

Notoriously, the Nicomachean Ethics lavishes attention on the practical virtues, explaining that they are dispositions to choose the ideal mean between extremes, dispositions that we acquire through training and repetition. Yet in the final book Aristotle adds that pure contemplation is to be preferred to virtuous practical activity. Is he telling us to spend our time doing philosophy in addition to being practically virtuous? Or telling us to forget practical virtue if circumstances allow, and spend all our time contemplating? As we’ve just seen in our examination of his metaphysics, Albert does think that humans achieve perfect happiness or “beatitude” through a kind of contemplation. It is a contemplation available to us in the afterlife, when the blessed will behold God “face to face.”

Perfect virtue requires that when we perform good actions, we are striving to reach the perfect good, which is God Himself. Albert here exploits an idea that was often

emphasized in medieval guidelines for administering the sacrament of confession: whether an action is sinful or not, and to what extent, depends on its circumstances.

Likewise, our conception of life’s ultimate end makes a difference to the goodness of our actions. If we just seek worldly virtue, that’s less perfect than if we seek God. Albert still admits that worldly virtue is a kind of happiness, even if it is a lesser one. Where Augustine said that only “false virtue” was available to the pagans of Rome, Albert thinks that even a pagan can become genuinely, if imperfectly virtuous. For pagans too can acquire the so-called “political” virtues through the process of habituation described by Aristotle. Furthermore, the happiness of contemplation can be achieved in this life. Such earthly contemplative happiness trumps the happiness of acquired political virtue, though it falls short of the perfect beatitude of the blessed in heaven. The upshot is that Albert’s ethics envisions three possible degrees of human happiness, lying respectively in the life of practical virtue, the life of philosophical contemplation, and ultimately the beatific vision. The first two were already described by Aristotle in his Ethics, but the third is known only in Christian theology. Ideally, the lesser kinds of virtue and happiness are stages on the way to ultimate beatitude: acting virtuously towards our neighbors is a kind of preparation and stepping

stone towards blessedness.

With Albert, he holds that our ultimate happiness can lie in the beatific vision alone. No created thing can satisfy the human will, because no matter how good a created thing may be, it is good only by participating in God’s more perfect goodness (ST 1.2 Q2 a8 resp).7 On this point Albert and Aquinas agree with their fellow Dominican Robert Kilwardby. He too emphasizes the difference between the mere “felicity” in this life and the full happiness or “beatitude” available in the afterlife.8 But, as in other areas of his philosophy, Kilwardby leans more towards the traditional Augustinian teachings. For him all philosophical speculation is justified by its contribution to our moral development, whereas Albert, following Aristotle, made contemplation an end in itself, and one that surpasses the life of practical virtue. Characteristically, Aquinas splits the difference. He agrees with Albert that contemplative vision is our ultimate end, but adds the more Augustinian point that the vision of the divine essence involves not just knowledge of God, but also love, and the delight one has in beholding Him (ST 1.2 Q3 a4 resp).9 Yet Aquinas was keenly aware of the tensions between Aristotelian and Augustinian ethics, as is abundantly clear from a set of disputed questions that he devoted to the topic of the virtues.10 His attempt to resolve those tensions begins with the very definition of virtue. He asks

whether virtue is correctly defined as “a good quality of mind by which we live rightly, which no one misuses, and which God works in us without our help” (DQV 1 a2). This definition was offered by Peter Lombard as a summary of Augustine’s teaching on virtue, and in the face of such authority Aquinas can hardly deny that it hits the mark. So he goes on to agree with the definition, adding just one apparently innocuous remark: the definition would still be accurate without the last phrase about God working virtue in us without our help. That part of the definition applies only to infused virtue, not to the kind of virtue we acquire by developing our natural capacity for goodness. Aquinas is not sliding into Pelagianism here. He would stoutly deny that natural virtue is enough to merit salvation and hence ultimate happiness. But the fact remains that virtuous acts can be performed, and virtuous character cultivated, with no special help from God. When we speak of such “natural” virtue, we do not mean that a virtuous character is born in us by nature, as if babies came into the world already honest, courageous, and generous. Babies do, however, come into the world with a natural ability to acquire these traits (DQV 1 a8 resp). Acquiring them takes training and practice, which is why parents coach children to perform the right kind of action repeatedly until it becomes, as we might aptly put it, “second nature.” Aquinas’ explanation of this point is a wonderful example of his ...

passages for his solution. Thus, he admits that Augustine seems to deny the possibility of natural virtue: “The life of all those without faith is sin…wherever knowledge of the truth is lacking, there virtue is false even if one’s behavior is excellent” (DQV 1 a9 obj 2).11 Since Aquinas believes, following Aristotle, that we can indeed acquire virtue naturally through habituation, he has to defuse this quotation. He does so by replying tersely (and unconvincingly) that such Augustinian remarks were meant to apply only to the higher virtues that lead us to true beatitude. In the next article Aquinas tacks back in the other direction. Now he asks whether virtue is always naturally acquired or can also be infused by God. Of course, he thinks it can be infused, despite evidence in Aristotle to the contrary (DQV 1 a10 obj 1). But it is too simple just to shrug and say that there are two kinds of virtue which arise in different ways. For one might wonder, if we can acquire some virtue naturally, why is this not enough? Why is divine infusion also needed? Aquinas poses the objection in the terms of traditional ancient ideas about virtue. Acquiring good dispositions means that our will ...

get you somewhere, but not to your ultimate destination. In the journey of life, that destination is God, and it is the theological virtues of faith, hope, and charity that enable us to order our choices to that most final of ends. A higher virtue like charity does not supplant natural virtue. It rather perfects the limited virtues we can acquire through our natural resources.12 What could Aquinas say to a pagan, or atheist, who says they are happy to settle for a life of natural virtue? Simply that they cannot hope to be truly happy that way. We are born with not only a disposition to acquire earthly virtue but also a natural yearning that can be satisfied fully only by the supreme good which is God. Like the airport shuttle, human nature points beyond itself, having the built-in resources to pursue and attain limited good, but also the purpose and desire for unlimited good. It’s no good objecting that we can know God even in this life, so that a taste of the supernatural is already available to us in the here and now. Remember, all our knowledge is grounded in sensation, and on that basis we can only reason to the existence of God, not to an understanding of what He is in His ...

making a colossal error, one with moral and not just abstract philosophical implications. For they are failing to discern and choose God, the...

The salvation we are promised through grace looks suspiciously like the theoretical activity celebrated in the last book of Aristotle’s Ethics. Yet one can with equal justice say that Aquinas works Christian values into the fabric of Aristotelian ethics.

This also helps to explain a feature of Aquinas’ ethics that I haven’t mentioned yet, which is that the virtues we can acquire naturally, like courage and justice, can also be infused by God. We might imagine God bestowing courage on a martyr who is faced by a gruesome death, without the martyr having had the long moral education needed to produce this virtuous character trait naturally.

The significance of the two alternative sources for virtue, natural and divine, may be clearer if we go back to the parallel I drew at the start of this chapter between morality and knowledge. It’s a parallel that Aquinas draws too. He points out the similarity between thinking that all knowledge is granted by divine illumination and thinking that all virtue is infused by God (DQV 1 a8 resp). In both cases Aquinas moves away from the strict Augustinian position common in his day. Knowledge and virtue can both be acquired, with some difficulty, as the realization of naturally inborn capacities. But in neither case is it enough to have what comes naturally. Natural reason is enough for philosophy but not enough for theology; the life of natural virtue is better than nothing, yet infinitely inferior to true happiness.

The idea that the cosmos is providentially governed or ruled by God goes back to antiquity.5 We may detect some survival of this idea in our modern talk of “natural laws,” which hints at a legislator behind the regularities of the universe.

A law of nature applies to all created things. To use an anachronistic example, this would be something like the law of gravity. By contrast the “natural law” is relevant only to rational creatures.6

You may notice that the natural law seems to have a close connection to what the medievals called synderesis (Chapter 26). This is our inborn urge to want what is good, comparable to our modern-day notion of moral conscience.

Like Albert, Aquinas appeals to the traditional idea of synderesis and gives it a rather intellectualist spin. It is simply our inborn tendency to accept the precepts of the natural law. The most fundamental precept of all is simply that one should do good and avoid evil

It may, therefore, be better to think of synderesis and the natural law as the source of our ability to reason about practical matters, and our tendency to go for whatever seems best, rather than as providing a set of rules to follow when we are deliberating.10 But why does Aquinas describe all this in terms of “law”? Why not talk of moral “conscience” instead, as did other thirteenth-century authors? The answer lies with Aquinas’ ambitious undertaking to integrate the natural law within a whole legal theory. For him, law is defined as “a certain dictate of reason for the common good made by him who has the care of the community, and promulgated” (Q90 a4 resp). That’s a bit of a mouthful, but each part of the definition seems reasonable enough. Laws have to do with rationality, since they serve as principles and reasons for

action; laws have the goal of securing the good for the whole group, or “community,” subject to them; laws derive from a legislator, the one who oversees that community; and a law must be made known to those subject to it, or “promulgated.” In the case of the natural law the legislator is God Himself and it is promulgated when its precepts are implanted in each human mind (90 a4 obj 1). As the term “natural law” suggests, we have it from our very nature, getting it “for free” so to speak. This doesn’t mean that people always adhere to the natural law, sadly, because humans do not always follow practical reasoning, as when they are overwhelmed by their irrational desires (Q94 a6 resp). So that’s why natural law qualifies as a type of “law.” But it is only one of four kinds of law recognized by Aquinas. The supreme law is what he calls “eternal law,” which is nothing but the principles by which God governs the whole universe. Eternal law touches all things, even if they are inanimate or irrational, not because things like stones or giraffes consciously try to put God’s law into practice but because they fall within His providential oversight (Q93 a4 resp). The natural law exists only within us as rational creatures, being our way of participating in this most general, eternal law. Natural law is thus the “impression of the divine light” in us (Q91 a2 resp and repl obj 1). Fundamental though it is for our ability to reason about the good and bad, the natural law is still not ...

Political legislation is guided by the same principles that ground ethical deliberation, with human laws being simply a determination of the natural law as applied to the circumstances and needs of a given community.12 Good human laws aim to bring all members of the community along towards virtue by preventing them from sinning and, more positively, by offering them enforced training (disciplina) in virtuous behavior (Q95 a1 resp). The reason we outlaw murder isn’t simply to prevent people from getting killed, though that is surely part of the point. It’s also to ensure that our community is full of people who would not even consider committing murder. Law does accomplish its objectives especially through the threat of punishment, but if all goes well, those who are subject to the law will internalize its values and cheerfully act in accordance with those values. When you go through life without murdering people, it’s hopefully not because you’re afraid you’ll get caught, but because that’s...

When he considers the question of whether one should ever break the law, he focuses on good laws rather than bad ones and asks whether it could ever be right to break a good law. Yes, says Aquinas, but only in the case of an emergency (Q95 a6 resp). His example is that though the gates of a city should not be opened during a siege, you might break this rule to let a group of the city’s defenders retreat back inside the walls. In less pressing circumstances one should seek to change the law instead of simply defying it. Furthermore, we should be reluctant to change laws, since that always comes with the cost of undermining custom and stability, even if the intended change is for the good (Q96 a2 resp). Just as only just laws are truly laws, so for Aquinas the true ruler is the one who aims at the common good.

The mixed construction also bears some resemblance to the limited monarchy often seen in the medieval period, which is presumably no coincidence. Under this arrangement there is indeed a single ruler but his governance is mediated through other officers, for instance judges. The ruler could be anyone, and he adopts his special role as the representative of all the people, even as his power is shared out among subordinates.