Note: this transcription was produced by automatic voice recognition software. It has been corrected by hand, but may still contain errors. We are very grateful to Tim Wittenborg for his production of the automated transcripts and for the efforts of a team of volunteer listeners who corrected the texts.
Peter Adamson: We're going to be focusing in this episode on Aquinas's relationship to Aristotle, especially as it bears on Aquinas's theory of knowledge. But let's start with a more basic question. Which texts by Aristotle did Aquinas actually know and how did he get access to them?
Scott MacDonald: One of the things that makes Aquinas an interesting figure in the history of the reception of Aristotle in the West is Aquinas is in the first generation of thinkers to have been raised on really the complete Aristotelian corpus. The bulk of the Aristotelian corpus was translated into Latin and made available in the West beginning about 1150, and it grew gradually from the logical texts, what we think of as the basic natural philosophical texts, the Physics and texts of that sort, and the Metaphysics and the Ethics, finally by about 1240 almost everything of Aristotle was available in Latin and known in, say, Paris where Aquinas was a graduate student. Albert the Great, who was Aquinas's teacher in Paris, was one of the leading first generation Aristotelians. He was an adult when all of Aristotle became available. So you might say his formation wasn't on the Aristotelian texts, but Aquinas, who was Albert's graduate student, really cut his teeth on the Aristotelian philosophy with Albert and had essentially all of the Aristotelian corpus available to him. And that's what makes him, in a way, a paradigm representative of the assimilation of Aristotelianism in the Latin West.
Peter Adamson: And scholars usually think they can tell the difference between Albert and Aquinas on that basis, right? Because whereas Aquinas seems to be a dyed-in-the-wool Aristotelian, Albert's often thought to have more Platonic or Platonist tendencies.
Scott MacDonald: Yeah, I think that's exactly right. One of the things that you can discern when you read them is there are certain Aristotelian principles that someone like Albert the Great is working to get his mind around, but you can see that it's not natural for him and he's having some trouble with it. But for Aquinas, it's come to him in pure form, and so he's much more fully formed as an Aristotelian.
Peter Adamson: And you've got to get him young. Moral of that story. But I guess that not all of Aristotle's works were equally important for Aquinas, so there are some works that are really central to his understanding of Aristotle, and they're not, for example, his works on zoology. Right?
Scott MacDonald: That's right. So some of the empirical works are less important. What we tend to think of as the big Aristotelian works were the big works for Aquinas. So De Anima informs his view of the nature of the human being and his views about thought and epistemology. Metaphysics is important to him. Aristotle's Ethics, the Nicomachean Ethics, is important to Aquinas. So the big texts that we think of, texts that we might not think of as among the most important of Aristotle's texts today that were particularly important to Aquinas include, for example, the Posterior Analytics, which shapes Aquinas's thought quite deeply and profoundly.
Peter Adamson: And he wrote commentaries on some of these.
Scott MacDonald: He wrote commentaries on most of the important works of Aristotle, and he's got big fat commentaries on the Metaphysics. And I mean fat on the Metaphysics, on the Ethics, on the Physics.
Peter Adamson: Yeah, up there with Averroes’s long commentaries.
Scott MacDonald: Yeah, in the same ballpark, I think.
Peter Adamson: Well, let's turn to the epistemological issues that we wanted to focus on. Aristotle is well known for upholding a more or less empirical or empiricist theory of knowledge. In other words, he thinks that our knowledge is entirely grounded in sensation or is at least mostly grounded in sensation. So first of all, is that actually how Aquinas reads Aristotle? And if it is, does he agree with that?
Scott MacDonald: That is how Aquinas reads Aristotle as essentially an empiricist about human knowledge. And he reads Aristotle as holding that all of our knowledge begins in sense perception, our sensory experience of the physical world. And Aquinas thinks Aristotle's right about that. And in doing so, he disagrees with a long and influential tradition in medieval thought, which sides with Augustine and the Platonist tradition. That side of the tradition holds that we can have direct access to, for example, the intelligibles through our mental faculty without needing to rely on sense perception for those kinds of things. So Aquinas diverges from an important mainline tradition in agreeing with Aristotle about empiricism.
Peter Adamson: So he thinks you have to work your way up from sense perception up to universal knowledge.
Scott MacDonald: It really all has to start from sensory experience. And so when you think about that for a minute, you can see where the difficulties are going to arise. On the one hand, the Platonists have it easy in accounting for our knowledge of intelligible matters like mathematics. It's easy because they just postulate that we can have direct access to the objects of that knowledge. The empiricist has to explain how we can get to that fancy knowledge starting from something as simple as seeing a dog on the street.
Peter Adamson: Yeah, they actually seem in a way to have the reverse problem though, because although the Aristotelians have to explain how you can get to this fancy knowledge, as you just called it, on the basis of sensation, the Augustinian Platonists need to explain why everyone doesn't have it. And so the Aristotelians can explain very easily the fact that you know about giraffes and I don't because you've gone and looked at some giraffes. So it seems to have something to do with our different experiences. The Augustinians can explain how we could get to abstract knowledge, but it looks like they've both got a problem.
Scott MacDonald: Yeah, it's typical of philosophical theories, isn't it, that you find the easy problems to solve and lying right behind those solutions are the difficulties.
Peter Adamson: Right. Well, actually way back when, when I looked at Aristotle's Posterior Analytics, which is one of the texts you mentioned as being important to Aquinas, one of the things I talked about is that Aristotle puts very high demands on knowledge, in the strict sense episteme. And one of them is this one we've just mentioned, which is that knowledge has to be universal. So how exactly does Aquinas think that you can go from these very everyday sense experiences to a position where you satisfy these demands in particular that you have knowledge that's necessary and universal and completely certain?
Scott MacDonald: It's not entirely clear how the account is supposed to work at every point, just as it is for Aristotle, and Aquinas follows Aristotle closely in these matters. But the linchpin in the account, as far as Aquinas understands it, is the existence of what Aquinas calls an agent intellect. Aquinas is interpreting Aristotle's De Anima, Book 3, in talking about the agent intellect. And unlike some of the philosophers in the Islamic tradition, Aquinas doesn't take Aristotle to be holding that the agent intellect is a separate intellect that is separate from individual human beings. Aquinas takes it to be a part of or a feature of our own intellects. So the role of agent intellect in Aquinas's epistemology is to take material that's been supplied, cognitive material that's been supplied by the senses and processed in the imaginative part of the soul, and extracting from that epistemic material what Aquinas calls forms. So the agent intellect, as it were, goes to work on material provided by the senses and abstracts from it universal forms.
Peter Adamson: When you say abstracts, should we infer from that that really that's a process of elimination? So I've seen all of these giraffes, and I'm trying to get to the universal of giraffe, and then what I have to do is get rid of the particularities of each individual giraffe I've seen, or does it actually enhance the particular forms that I've seen by bestowing universality on it? Or are those somehow the same thing?
Scott MacDonald: I think it's very difficult to say …
Peter Adamson: That’s why I’m asking.
Scott MacDonald: …what Aquinas thinks the exact process is supposed to be. Aquinas will sometimes tell a story very much like the story that Aristotle tells at the end of the Posterior Analytics, and it's notoriously difficult to tell what Aristotle has in mind in that story. There's a kind of metaphysical slogan that Aquinas sometimes uses that mirrors, even if it doesn't explain, his idea about what the agent intellect does. He says sometimes that forms are particular in concrete things, but they are universal in mind. And so he wants to have his cake and eat it too. That is, he wants to say that out there in the external world there aren't universal forms. They're only mental beings, but nevertheless in some sense it's the same form that's particular in the individual that's the subject of sense perception that ends up in the intellect after agent intellect has done its work that's now universal in nature. So he wants there to be a seamless connection between the particular form out there and the universal form in intellect when agent intellect has finished its work.
Peter Adamson: And it better be a particular version and a universal version of the same form. Otherwise if I have a form of giraffe in my mind it wouldn't be knowledge of the giraffes running around on the savanna.
Scott MacDonald: Exactly.
Peter Adamson: That way that you just put that reminds me of one of the philosophers from the Islamic tradition you just alluded to who obviously were very influential on Aquinas even when he didn't agree with him. This is Avicenna. Because Avicenna actually argues that if you have universals in your mind that that in itself proves that the mind is immaterial. So that leads him into a dualist conception of the soul. In other words he argues that the rational soul is a different kind of substance from the body. And Aquinas does, doesn't he, use the same sort of argument to show supposedly that the soul is immaterial?
Scott MacDonald: Yeah. Aquinas thinks that if the intellect weren't immaterial, it wouldn't be able to play the role of abstracting or hosting, having, being the possessor of universal forms. So the fact that we can think universally, Aquinas thinks, is evidence that the intellectual part of the soul doesn't have an organ and is itself immaterial. Nevertheless, Aquinas is perhaps less of a dualist than Avicenna is about these matters. Aquinas is committed to what he thinks of as Aristotelian hylomorphism as the best way to understand the nature of a human being. That is, he thinks that human beings are by their very nature combinations of form and matter, the rational soul being the substantial form and matter, or technically prime matter, being the matter of a human being. So Aquinas doesn't think that we have a substance, intellect, which is a different substance from our bodies or our matter. We're one substance, a hylomorphic substance, but part of the rational soul, the intellective part, must be itself immaterial and function independently of a material organ in order to think universal thoughts.
Peter Adamson: And that just happens to go very nicely with the Christian doctrine on the resurrection of the body.
Scott MacDonald: That's right and Aquinas then is able to say things like, once a human being dies, the soul will not be complete until it receives a resurrected body again, because a soul apart from a body is in certain respects an essentially incomplete being.
Peter Adamson: Yeah, it's interesting that because Avicenna was also an empiricist, he would say, well, you need the body to actualize the intellect because otherwise you're not going to be able to get to these universals. But once you've done that, you can get rid of the body, you don't need it anymore. So why does Aquinas think you still need it once you've actually gotten up to the level of having an intellection?
Scott MacDonald: I think his main point is simply the metaphysical one. I suppose we can talk about metaphysical needs, but substantial forms are by their very nature designed to or fitted for being the forms of the things they're forms of. So you might say there's a kind of metaphysical ineptitude in the existence of a form without matter, a substantial form without matter.
Peter Adamson: Like an actuality floating around with no corresponding potentiality.
Scott MacDonald: Yeah. In fact, I think he struggles a bit as one might imagine to describe how it all works once the resurrected body and soul have been reunited. I'm not sure he has a clear view about why we would need to have a body in that situation.
Peter Adamson: This mention of pure actualities floating around without potentialities brings us nicely on to the highest possible topic of contemplation, which is God. And it seems to me that what you were saying about Aquinas's empiricism poses us with another problem here because obviously God is a purely immaterial, purely actual substance and is not the sort of thing that you can grasp with the senses. So if Aquinas is really going to be serious about following Aristotle's epistemic theory, he's going to be an empiricist, then how does he think we could possibly ever have knowledge of something like God, or for that matter, an angel, so any immaterial substance?
Scott MacDonald: Aquinas thinks we get knowledge about immaterial things like God from two different sources. Obviously as a Christian, Aquinas thinks that God can pass along information as it were. So there's revelation, and revelation contains information about God's nature and, disregarding whatever the mechanisms or means might be, the ultimate source of revelation is God himself. So God tells us things about himself in Christian revelation, and Aquinas says there's good reason for that because otherwise it would take us a long time to figure out very important stuff. We'd get a lot of it wrong and only smart people would be able to figure it out. So Aquinas thinks there are good practical reasons for revelation. The other side of the story though is Aquinas thinks that we can, even given his empiricist restrictions, achieve what we might call natural knowledge of God or philosophical knowledge of God. So Aquinas believes that we can figure out a lot about the nature of the causes of things from the features of the effects they cause. So he believes certain causal principles about the effects resembling their causes in certain respects. So Aquinas thinks that we can start with God's effects. God is creator of the universe, including the physical world that we can access through our senses. So all of the bodies that we can access with our senses potentially provide us information about their ultimate cause, the divine being. So Aquinas thinks we can start from sensory experience, apply certain causal principles, and reach interesting results that we can then leverage with other kinds of reasoning to learn quite a bit about the divine nature. And that's the way in which Aquinas's famous Summa Theologiae begins. Question two, he asks whether God's existence can be demonstrated. The answer is yes it can, beginning from things that are self-evident to the senses using causal principles. And the five ways each begin with an observational premise, something that an empiricist can be relatively happy with, and then proceeds on the basis of causal principles.
Peter Adamson: It's striking though that he says that you can demonstrate the existence of God in that way, because going back to the Posterior Analytics, we mentioned already that it's a very demanding theory of knowledge. And one of the demanding criteria that Aristotle gives is that if you're really going to demonstrate something so that you achieve knowledge in the strict sense of that thing, you're supposed to move from causes to effects, not from effects to causes, right? Because causes are the explanations of things, and demonstration or understanding is supposed to be explanatory. So, doesn't that mean that actually you cannot have a science of God in the strict sense, at least not in the sense that Aristotle's described in the Posterior Analytics?
Scott MacDonald: We have to be careful there. Aquinas does subscribe to the view he finds in Aristotle's Posterior Analytics, but it's a nuanced view. So he takes the very strict conception of demonstration and correspondingly demonstrative knowledge that comes in the early part of the Posterior Analytics, not as describing necessary and sufficient conditions on demonstration or knowledge, such that if you don't meet them, you don't have demonstration or you don't have knowledge. He takes them to be an account of what we might think of as the gold standard for demonstration or for knowledge, that is, the paradigms, if you think now in a sort of Platonist frame of mind about paradigms. Paradigms are things that concrete instances strive to participate in to some extent without being that thing itself. So Aquinas thinks there are ways in which forms of argument and certain kinds of epistemic states can approximate the very rigorous description provided at the beginning of the Posterior Analytics without fulfilling all of them. So there are ways in which an argument can be a demonstration without satisfying all the conditions. And a good example of that is the proofs for God's existence, which argue from effects to causes that obviously fails to satisfy the condition on gold-standard demonstration, which you mentioned, that is, identifying the causes of the effects and being explanatory in, you might say, the most robust sense. Nevertheless, Aquinas thinks you can get something that counts as demonstration, though not gold-standard demonstration, by giving up that criterion and satisfying it in another way via causal principle that leads you to causes from effects. So that's one kind of example of the way in which a demonstration which isn't paradigm demonstration is nevertheless legitimate demonstration, and the sort of knowledge to be gained by that demonstration while not being paradigm knowledge is nevertheless legitimate knowledge.
Peter Adamson: What about the other side of the coin, which is the kind of theology that proceeds from revelation? It might seem strange to us since nowadays we think about faith as the attitude you take towards a belief where you don't have certainty or you don't have proof. That's one way of thinking about faith. So it might seem strange to us that he thinks that theology based on revelation and hands-on faith could be a science, but he does call it a science. He calls it a sacred science.
Scott MacDonald: That's right. So he sometimes calls it sacra doctrina, sacred teaching, and he thinks that it is a science, though again he's quite clear that it isn't a paradigm science. So he recognizes that it doesn't satisfy the conditions laid out for episteme haplos or scientia simpliciter at the beginning of Posterior Analytics. In this case, the basic idea is that science is understood now as organized bodies of knowledge that have a unified subject matter. Sciences can be related to one another. So for example, this is the sort of thing Aristotle himself says, someone who works on optics, there can be a science of optics. It largely involves using geometrical principles and ideas, but the optician isn't a geometer, that is, he needn't be a geometer. He can get the principles of geometry from the geometer. Now that's going to be okay provided the geometer is doing his work properly. So you might say the first principles of optics can be inherited from geometry. They're not real first principles. The geometer is doing that part of it, but the optician is taking them as first principles. They're inherited from what we might call a higher or more basic science. So that's an idea Aristotle has, and that's the idea Aquinas develops to explain how sacra doctrina, which begins from articles of faith, can nevertheless be a science despite the fact that its first principles aren't, you might say, honest-to-God first principles.
Peter Adamson: So to speak.
Scott MacDonald: So what happens in this case, Aquinas says, is the articles of faith are inherited, as it were, from a higher science, namely the science that God himself knows. So God has access to the first principles, the real first principles, and hands-along things that the theologian can use as first principles in sacra doctrina. So sacra doctrina is like optics. It's a subordinate science that relies on another science, in this case, the divine science.
Peter Adamson: So the reason that for us it's not an ideal science is just that we don't have the ability to go up and prove that the first principles are true.
Scott MacDonald: Yeah. So what we take as first principles when we do sacra doctrina aren't first principles for us, and in fact they may even be derived in the divine science. We take them on the divine say-so, so to speak, in the way the optician takes something on the geometers’ say-so. But Aquinas is quick to point out that if you abstract from our particular perspective on it, we're actually in better shape in sacra doctrina than otherwise, because what more secure first principles could you have, ultimate first principles could you have, than those which God himself knows in the divine mind.
Peter Adamson: Right. Actually, this brings me to the last thing I was going to ask you, because Aristotle lived before revelation, so he's not in a position to avail himself of these principles, and thus he's not in a position to do sacra doctrina, and that would lead us to expect that Aquinas would think that Aristotle must be missing out on something that someone like Aquinas isn't missing out on. But I'm still wondering what Aquinas thinks about Aristotle if you just go in terms of natural reason. Does he think that Aristotle has achieved as much as anyone possibly could using the natural light of reason, or does he think that although Aristotle is a very, very good philosopher, he sometimes makes mistakes? I mean, in several of the things you've said already, it became clear that it looks like he's trying to find ways to make Aristotle come out true, but he is willing to criticize Aristotle on occasion.
Scott MacDonald: He's certainly clear that he believes some of the things that Aristotle believes are false. So, Aquinas does not believe that the world has no beginning in time, as Aristotle believes. So he's quite happy articulating views that are incompatible with views of Aristotle. Having said that, it doesn't happen very often, and interestingly, Aquinas often finds himself arguing against what he thinks of as more radical interpreters of Aristotle, Islamic thinkers or Latin thinkers in the West influenced by Islamic thinkers. He often finds himself arguing against them in their adoption of what they take to be Aristotelian principles. For example, the defense of the eternity of the world. He finds himself arguing against them not simply about the facts, but about whether they've interpreted Aristotle correctly. So Aquinas thinks in many cases the radical interpreters of Aristotle haven't read Aristotle right. So Aquinas finds more agreement between Aristotle and his own Christian metaphysics and epistemology than some people who outwardly claim a greater allegiance to Aristotle.