Medieval Philosophy

by Peter S. Adamson

Normally, though, Aquinas doesn’t seem to think you can simply “read off” moral precepts from observations about the natural world. This has led to a controversy about how exactly he thinks the natural law works.17 Is the idea that humans have certain natural and essential functions, from reproduction to contemplation, and that the natural law declares to be good anything that will promote these functions? Or is it simply that reasoning about the good is a natural, inborn tendency, and that Aquinas thinks that this establishes the universality and inevitability of such reasoning? Nowadays many moral philosophers are opposed to the whole notion of natural law, because it seems to imply that certain actions are good to us because they are “natural.” This idea may seem sinister, given that it could be used and indeed has been used to forbid such things as homosexuality and contraception. It may also seem downright silly: is it wrong for me to travel by plane, since it is unnatural for humans to fly? On the alternative interpretation of Aquinas, none of these problems arises. The “natural” part of the natural law is just supposed to mean that part of being human is having a tendency to prefer, and use reason to pursue, the good.

Take, for instance, the topic of warfare. When he was itemizing the precepts of the natural law, the jurist Gratian included on his list the idea that “violence should be repelled with force.” This looks like permission to wage war in self-defense—something most of us today would find reasonable enough. But we’re talking about philosophy in medieval Christendom, and didn’t Christ tell us to turn the other cheek? How, then, could Christian intellectuals give a rationale for the state’s use of violence?

The pacifist sentiments of Christ notwithstanding, there were circumstances in which Christians could and indeed should take up arms. Despite the religious context,

medieval discussions of “just war” can seem eerily familiar, as when we find them wondering whether the use of “ultimate weapons” can ever be justified (though they meant by this crossbows, not atomic bombs) or what legal conditions need to be satisfied before war can justly be declared.

The important thing, to Augustine’s mind, was the intention that leads one to engage in warfare or other violence. Though peace is our ultimate goal, even in the midst of war, we are permitted to break the peace temporarily in order to combat and to punish sin, to defend the faith with arms as well as words.

Isidore of Seville summed up the legal standpoint on war as follows: “A war is just when, by a formal declaration, it is waged in

order to regain what has been stolen or to repel the attack of the enemies.”3 This passage was quoted prominently in Gratian’s Decretum (§2.23.2.1) and thus set the template for pretty much all medieval discussions of war. At the heart of Isidore’s definition is the idea that you are always allowed, morally speaking, to defend yourself and your property.

Violence in general and war in particular were justified as a last resort, to be used when legal measures could not be brought to bear.

In a real courtroom setting the punishment must fit the

crime, and our legal authors likewise stressed that legitimate violence must be proportional.

Remember, though, Augustine’s point that warfare is justified by the good intention of those who declare the war and fight it. If your aim is really to punish and prevent sin and to restore peace, that in itself should preclude many of the actions we would today call “war crimes.”8

The Dominican writer Roland of Cremona stated that soldiers who were being dragged into an obviously immoral military endeavor should refuse to participate.

Furthermore, authorities like Augustine taught that war leaders had the moral responsibility for unjust wars, effectively absolving the front-line soldiers from the overall sinfulness of the conflict. The general advice to the medieval warrior was, then, just to follow orders.

Here we arrive at another key question: on whose authority can war justly be waged?

But just war requires rightful authority, and no medieval author could deny that there is one authority that outranks all others: God’s. Hence all agreed that the wars fought at God’s explicit command (as recorded, for instance, in the Old Testament) were thereby justified. From here it was only a short step to seeing the Pope as having legitimate authority to declare war, since the Pope is God’s representative on earth.

But how could this be squared with the idea that just wars need a just cause? The Crusades would seem to be a clear case of an unprovoked and offensive war, not a case of self-defense.

Aquinas brings his characteristic clarity and nuance to the issue. He identifies three criteria by which wars are justified: they must be fought with legitimate authority, for a legitimate reason, and with the right intention (Q60 a1).

This makes clear an assumption that underlies much of the medieval theory of war: figures like princes, emperors, and popes have the authority to declare war precisely because there is no legal authority above them to whom they might turn in order to settle disputes. On the issue of just cause, Aquinas connects the usual ideas about self-defense and rectification of injustice to Aristotelian political philosophy. Wars are just when they are waged to defend the “common good,” the same goal rulers should have in view when they are making

laws.14 Finally, there is the third criterion of good intention. It’s here that Aquinas’ most philosophically fruitful idea comes in. It’s called the “doctrine of double effect.” The classic text on this is found in his treatment of a question that we’ve seen to be closely related to the topic of just war: is it all right to kill an attacker in self-defense (ST 2.2 Q40 a7)?15 Aquinas says yes, and reasons as follows. It may be that you use force against an attacker solely with the intention of protecting yourself and kill the attacker in the process. The fact that you didn’t intend to kill him makes this case very different from one where you deliberately murder somebody. The difference is indeed so large that it excuses you from moral (as well as legal) blame. In general, we may be justified in performing actions even if they have unwelcome side effects, and the justification turns at least in part on the fact that we don’t intend those side effects.

Persuasive though such cases are, the doctrine of double effect turns out to be very difficult to formulate and defend with total precision.16 For starters, it may seem to give us far too much moral license. Couldn’t I just excuse any horrendous consequence of my actions by saying that the consequence isn’t one I intended?

Proponents of the doctrine of double effect, like medieval just war theorists, are careful to warn that our actions must be “proportionate.” In that case, though, why do we need the idea of double effect at all? We could just say that a responsible agent should weigh up all the foreseeable consequences of her action, both welcome and unwelcome. If the action will produce, all things considered, the best outcome among all the things she could do in her situation, she should perform that action. The response to this, I think, would be that the doctrine of double effect is designed for people who don’t like to think this way. The idea that you can weigh up all the good and bad consequences, striving to get as beneficial a mix as possible, is characteristically utilitarian, a way of thinking that could in principle license you even to engage in torture and Crusade-style mass murder so long as the consequences are good enough. The double effect theorist

is more likely to be someone who thinks that some kinds of action are simply never permitted, at least if they are chosen directly.

The unwanted result is not something you intended, but something you simply couldn’t avoid. As Aquinas says, it is only “accidentally” related to the action you chose to perform

But I will mention that, even in less contentious cases, there are further objections for the doctrine to overcome. Why should our intentions make so much moral difference? Isn’t the decisive thing, rather, what you can reasonably be expected to foresee as the result of what you do? Then, too, it seems that any action can be described in various ways. The historian says, “The Crusaders went on a mass killing spree, slaying Cathars and Christians alike,” where the Crusaders themselves would say, “We eliminated heresy from the bosom of the community, and sadly a few

devout Christians got killed in the process.” From this perspective double effect looks like an invitation simply to justify your action by describing it in the best possible light.

The concept of the transcendentals may have developed in part to emphasize that all of creation is good, not an arena in which good and evil principles clash, as the Cathars believed.

In the late 1260s Bonaventure had identified certain philosophical teachings as “heretical,” singling out three in particular: determinism, the eternity of the universe, and, worst of all, the notion that all of humankind shares one single intellect.

In another treatise on the days of Creation, he added as a fourth heresy the idea that happiness is attainable in this life, and complained that some of his contemporaries were turning the wine of theology into water by mixing in pagan teachings.

In that same year Aquinas wrote a work attacking the idea named by Bonaventure as being particularly heinous, namely Averroes’ view that we all share one single mind. Then, there is a treatise called Errors of the Philosophers, which is ascribed to Aquinas’ student Giles of Rome, though its authenticity is doubted. It names and shames philosophical authorities, including many from the Islamic world, for their unacceptable doctrines. Aristotle too comes in for criticism. He is not to be blamed for failing to endorse the truths of faith, since these may have been beyond his ken, but for falsely asserting things contrary to the faith when reason should have enabled him to know better.

Let’s take the example just mentioned, the proposition that form is divided only through matter. The issue here is one familiar to us from our look at the twelfth-century thinker Gilbert of Poitiers (Chapter 16): how is it that each individual comes to be the particular individual that it is?

Each thing is made an individual by its matter. Thus, the four Marx Brothers are the same in form, essence, or species, because they are all humans.

But Aquinas questioned this consensus. For him all matter is spatially extended, so angels cannot be made of matter. How then does it happen that there is more than one angel? Following the logic of his metaphysical commitments with complete consistency, he assumed that each angel is unique in species. In other words each angel is a distinct type of thing: the difference between the angels Michael and Gabriel is like the difference between humans and horses.

I say “apparently,” because Aquinas actually didn’t take himself to be denying that God lacks the ability to make more than one angel of the same type. His point was that it is just incoherent to suppose that there are two distinct immaterial things of the same species. For God to make two angels that are the same in species would be like His creating a round square or dry water.

A case for the last option was mounted by the historian Pierre Duhem. He suggested that Tempier unwittingly helped to pave the way for the rise of modern science by condemning certain ideas of Aristotelian science that actually needed to be rejected if progress was to be made. While Duhem’s version of this thesis is now usually seen as an oversimplification, there is still a plausible argument to be made in favor of his basic idea.14 The argument centers especially on the idea that God has the power to do things that are naturally impossible, even if He cannot bring about actual contradictions (art. 17). As the medievals would say, God has the “absolute power” to

do anything whatsoever, as long as no inconsistency results.

This was a real blow against Aristotelian science, which was wholeheartedly committed to the impossibility of void. But it can also be taken as an unintentional blow in favor of scientific progress, since, of course, void is in fact possible.

But 1277 marks something more specific: an institutional effort to thwart the pursuit of philosophy independently of theology. To quote Luca Bianchi, a scholar who has written extensively on the condemnations, “Tempier was not so much interested in distinguishing philosophy from theology, but in subordinating the one to the other.”15 If we think of philosophy as an autonomous discipline that should be allowed to follow reason wherever it leads, then philosophy does seem to have been hampered by the condemnations.

In his final and longest commentary on Aristotle’s treatise On the Soul Averroes made the striking, not to say bizarre, claim that all humans share one single intellect. Bizarre or not, he had good reasons for saying this.5 When both you and I understand something, we are understanding one and the same thing. If we’ve both taken a class on giraffe biology, we wouldn’t expect you to have got your head around one nature of giraffe while I have come to grasp some other nature of giraffe. Rather, we should both know about the same nature. But, in that case, what could possibly differentiate your understanding about giraffes from mine?

The mind that grasps the nature of giraffes has no special connection to your body, because its activity is purely immaterial. But, as we’ve seen throughout this book in various discussions of individuation, without a relationship to matter it would seem that there is no way for multiple things to be distinguished one from another. We are forced, then, to say that there is only

one act of understanding that grasps the nature of giraffes. When you and I complete our course on giraffeology, we have both come to engage in this single act of understanding, the activity of a single mind. The reason that you and I enjoy the exquisite experience of knowing all about giraffes, where other people do not, is that our sensations and memories are being used as the basis for a universal act of understanding about giraffes. The universal intellect is getting no help from the giraffe ignoramuses, so they don’t get to share in that experience.

However, the mind is only one power or capacity of a single soul, which is the form of the body, as Aristotle also says clearly. Aquinas accuses the Averroists of violating this teaching by making the intellect completely different from the human soul

Of course, it was far less mainstream for him to press on, following in the wake

of Averroes, and point out that in that case there will be nothing to differentiate one separate intellect from another. We just saw in Chapter 41 that one of the propositions condemned at Paris was that there cannot be many immaterial things of the same kind, like angels, and saw too that Aquinas himself could have been the target of this condemnation. He thought that each angel must be unique in species, since it would otherwise be impossible for one angel to be distinct from another. So, when Siger started suggesting in the 1260s that Averroes’ idea of a single intellect wasn’t so crazy after all, he was himself being far from crazy. Siger was simply combining a standard idea about the nature of the human mind, namely that it is independent from body and distinct from any bodily form, with a principle that even Aquinas admitted, namely that anything with a truly immaterial nature must be unique.

Instead, Siger’s considered view would seem to be that competent philosophical reasoning can lead to beliefs forbidden by faith. Though we should not be convinced by such reasoning, neither should we expect that we can find a flaw in the arguments. Rather, this is just a sign of our own limitations, limitations that affected even so great a thinker as Aristotle—who was himself only human, as Siger remarks.7 One might say, then, that for Siger philosophy can, at least on some more difficult topics, reach only provisional results. These results need to be checked against and potentially corrected by faith, because philosophy is not always in a position to rectify itself.

The philosopher must proceed on the basis of natural reasoning and, insofar as we are doing philosophy, we shouldn’t question the deliverances of this reasoning. In fact, we should even deny anything that conflicts with our scientific principles, for example that a dead person could return to life. But any arts master can also take off his philosopher hat and assume the role of a pious believer. With his Christian hat on he will readily admit that God can and does do things that could never be brought about by natural causes.

Boethius’ solution to the conflict between reason and faith does allow for the kind of doublethink mentioned at the beginning of this chapter. Consider the geologist who is also a strict creationist. She might say that she isn’t really being inconsistent, but just taking two different points of view on the question of where the universe came from. During the week she pursues an answer using the tools of science, and on the weekend she accepts a wholly different explanation on the basis of faith. This may seem irrational; yet Boethius would say it is anything but. To the contrary, it makes space for the purely rational endeavor that is science. There is no conflict between reason and faith and, in fact, there cannot be such a conflict, since the philosopher readily admits that he is not speaking of what is the case “absolutely” but only of what follows from the principles of his science (52).10 The implicit message is that the bishop of Paris and the theology faculty should back off and let the arts masters get on with their business of expounding Aristotle, an autonomous enterprise with its own ground rules. It poses no threat to the faith, since faith involves stepping outside or rising above the discipline of rational science. Put this way, Boethius’ proposal doesn’t sound particularly shocking, and indeed it wasn’t. Consider one remark he makes: “When someone puts aside rational arguments, he immediately ceases to be a philosopher; philosophy does not rest on revelation...

Now, in the 1270s, it is tendentiously being presented as an admission that reason and faith reach two contradictory truths, amidst accusations of error and heresy.

For him the two cooperate by making distinctive and valuable contributions to a unified body of demonstrative science. Human reason is augmented with the addition of new principles taken from revelation, but reason is never corrected or overridden by faith, as Boethius would have it. For Aquinas reason does exactly what Aristotle promised, establishing necessary conclusions on the basis of indubitable first principles.

In a sense Aquinas’ goal was the same as the one pursued by Siger and Boethius. All three sought to make space for pure rational inquiry within the institutional framework of the university. Siger and Boethius attempted to do so by carefully qualifying their philosophical claims. Siger, stung by the condemnations, framed his exegesis of Aristotle with warnings about the limited competence of human reason. Boethius admitted that natural reasoning can always be trumped once supernatural phenomena are taken into account. But these were rather precarious ways to secure an autonomous role for science. Much better would be to show that science establishes truly reliable conclusions, without having to worry that these conclusions can be shown to admit of exceptions or just be outright false from the standpoint of faith.13 This was Aquinas’ solution. He went so far as to integrate theology itself into a thoroughly Aristotelian picture of human knowledge, enthroning it as the new queen of sciences, which both draws from and contributes to rational inquiry. In this respect, Aquinas was a more radical Aristotelian than either Boethius or Siger.

For them something that always exists cannot fail to exist. So asking whether the universe has always existed could seem tantamount to asking whether it had to exist, in which case God had no choice but to create it. By the same reasoning, if you could prove that the universe is not eternal, that would prove that it did not have to exist. And this would seem to