Peter Kail is University Lecturer in the History of Modern Philosophy at St. Peter’s College, University of Oxford. For our belated celebration of David Hume’s 300th birthday, Prof. Kail joins us to discuss Hume’s life and philosophical legacy. You can listen to our interview with Prof. Kail by clicking here.

Hume’s work has had an enormous impact on contemporary thought about induction and moral psychology, to name just two. In our interview, Prof. Kail discusses the ways in which Hume’s influence in these areas rests on some significant misunderstandings of his own views.

Take the case of induction. An inductive inference draws a conclusion about the way the future will be (or would be) based on the way things have been in the past. We make inductive inferences all the time. For example, I believe that the cup in my hand will fall to the ground when I release it. In fact, I’m quite certain that this will happen, because every time I’ve dropped a cup in the past it has fallen to the ground. Hume is often thought to be a skeptic about induction, meaning that he thinks we are not justified in inferring things about the future from facts about the past. This way of reading Hume is understandable. After all, Hume does say that we don’t derive an idea of causal regularities from observation or from anything we know a priori. But those seem to be the only options—how else could we be justified in believing in these regularities? And if I’m not justified in believing in these regularities, how can I be justified in inferring things about the future from facts about the past?

(NOTE: what we can know a priori is, roughly, what we can know without first having to observe (or remember, or be told about, or infer from) the way the world is. The same idea is sometimes expressed as the thought that what we can know a priori is what we can know through reason alone. Mathematical, logical, and (some) conceptual truths are the standard cases of things we can know a priori. For example, I know that 2 + 2 = 4 without having to make any observations or gather any other information about the way the world happens to be. But I cannot know, say, whether you are now wearing a red shirt except by looking to see whether you are, or by being told whether you are, or by inferring that you are from something else I know about the world. As such, that 2 + 2 = 4 is an a priori truth, but that you are now wearing a red shirt is not.)

For generations after Hume, philosophers have tried to come up with an account of causal regularities and our knowledge of them that would defeat Hume’s skepticism. Prof. Kail claims that while these efforts are philosophically important, it is a mistake to think that these are really responses to Hume himself. Hume thinks that we make inductive inferences because we are habituated to expect certain events to follow others, not because we are responding to anything we’ve directly observed or to a piece of sound a priori reasoning. But that doesn’t mean we’re not justified in making these inferences, or that there is no good reason for us to do so. It just means that the fact that there is a good reason to make inductive inferences does not explain why we in fact make them.

Hume thinks we’re perfectly justified in inferring things about the future from facts about the past, because our inductive inferences do in fact track regularities in the world. His point is just that our ability to track these regularities is just a feature of the way our brains and sensory faculties are wired, and so is really no different from the way non-human animals track regularities through perception, instinct, and conditioning.

Hume is also credited with a particular view about what it takes to motivate us to act, commonly known as the Humean Theory of Motivation. The basic claim of the Humean Theory is that desires and similar states are necessary to motivate us to act, while beliefs are not sufficient. For example, my belief that the apple on the table is a tasty treat cannot motivate me to walk over and eat it all by itself. Beliefs just don’t have the right kind of causal oomph to make me do anything. To be motivated to go eat the apple, I need to have a desire as well, say a desire to eat a tasty treat. While it might be the case that I have to have certain beliefs about the world in order to be motivated anything in particular, our actions are always at least partly caused by our desires and similar states.

The Humean Theory raises important problems in moral psychology and metaethics, and Prof. Kail notes again that while Humeanism about motivation is certainly important and interesting, it would be a mistake to think that Hume himself is a Humean about motivation. The mistaken attribution is due to a misidentification of belief and what Hume refers to as “reason.” Hume thinks that reason cannot motivate us to act all by itself, but that is because Hume thinks reason is just a faculty of comparing things. His claim that reason cannot motivate is not meant to apply to beliefs. In fact, Hume thinks that beliefs can motivate us to act. In particular, he thinks we can be motivated to act on the basis of beliefs about pleasure and pain. Humeanism about motivation, then, differs significantly from Hume’s own views on the subject.

Our interview with Prof. Kail closes with a discussion of Hume’s critique of religious belief and his legacy as a naturalist. Hume serves as an inspiration to many contemporary philosophers because of his unrepentantly naturalistic approach to philosophical questions, and his commitment to understanding human beings and human phenomena as part of the natural world. This commitment comes through in his attempt to explain the emergence of religious belief in a way that doesn’t assume that any supernatural phenomena exist. This way of approaching philosophical problems is now commonplace, but it is a testament to Hume’s brilliance and intellectual courage that he was already doing this in the 18th century.

Alex Langlinais