Class notes for 13 January

Main points

We discussed three topics. (1) constant conjunction, (2) reason and causal inferences, and (3) Hume’s theory of belief.

(1) After retracing the steps that brought us to constant conjunction, I tried to answer Katie’s questions about constant conjunction.

(2) There are two possible explanations for why we make causal inferences. Either we are “determined by reason” or we are determined by “a certain association and relation of perceptions” (

Hume dismisses the explanation involving reason on the grounds that it depends on our being able to found the Uniformity Principle (see — it’s in italics). We talked about why he would have thought that: conclusions of reason are certain and we have certainty only if we can found the Uniformity Principle. We also talked about why he thought we could not found the Uniformity Principle: we can always imagine its being false.

That leaves the explanation involving the association among ideas.

(3) What is the difference between merely thinking about something (“conceiving,” in Hume’s lingo) and believing it? Hume’s answer is that believing involves having a particular kind of feeling about an idea: one that is especially lively or forceful (plus some other conditions). Merely conceiving of something involves having an idea without this feeling of force or liveliness.

I said that this was not satisfactory and concluded with a question: what does Hume think a feeling is?

Reason and causal inferences

In 1.3.6, we are told that there are two possible explanations of why we make causal inferences: either “we are determined by reason” to make them or we are determined “by a certain association and relation of perceptions.” (

We can break the discussion of reason into two parts: (a) if we were determined to make causal inferences by reason, we would have an argument to found the Uniformity Principle. (b) But there is no such argument. That is what 1.3.6 tries to establish.

That means the other story must be correct. Spelling it out is what 1.3.7-14 are about.

Concerning (a), we talked about why reason would have to have a founding argument for the Uniformity Principle. Roughly, this is a necessary condition of reaching a certain conclusion, one whose denial is inconceivable. Since the conclusions of reason are supposed to be certain, it’s a necessary condition of causal inferences being a conclusion of reason.

(This helps, a little, to address Justin’s question about the apparent mixture of two projects here: one concerning our justification for believing things, the other concerning the explanation for our believing things. Reason entails certainty and certainty entails justification. So, showing there is no justification for causal inferences means we are not certain about them and, consequently, that they cannot be the product of reason.)

Concerning (b), there are two possibilities: the Uniformity Principle could be demonstrated to be true or there could be a probabilistic argument for it. Neither sort of argument would make the Uniformity Principle certain: we could conceive of its being false.

This lead to some discussion of how to decide whether something is conceivable or not. I think that’s a real problem for Hume, but perhaps it is less pressing here. It seems pretty clear to me that we can conceive of nature’s apparent uniformity changing — I can imagine the chalk going up when dropped, for example.

Reason as an explanation

Finally, I noted some odd features of 1.3.6.

For example, reason is a candidate to explain why we make the causal inferences that we do. Hume asserts that, if this were so, we would use the Uniformity Principle and he argues that this is not so in the way sketched out above. But it seems obvious that we do not use the Uniformity Principle and so there is no need for much argument.

Children and animals make causal inferences but do not think of the Uniformity Principle. Adult human animals make causal inferences too and, I’m willing to bet, none of you thought of the Uniformity Principle before reading (which you have done, right?). Hume himself says that we make causal inferences without any such thought at all. That’s what the man standing on the river bank does (

So why didn’t Hume just say this? “If we used reason to make causal inferences, we would think of the Uniformity Principle in making causal inferences. But we clearly don’t do that [example of the man at the river bank here]. Therefore, reason does not determine us to make the causal inferences that we, in fact, do make. Period.” Why did he think he had to give all of those other arguments?

Update, 17 Jan: For more on this, see the page on the Uniformity Principle.

A second oddity is this. As Justin pointed out, Hume did not need to go through the complicated story about how a probabilistic argument for the Uniformity Principle would be circular in order to make his point. As long as we can conceive of the Uniformity Principle’s being false, reason could not use it: the conclusions of reason cannot be conceived to be false but that would not be so if reason used the Uniformity Principle. Hume’s claim that we could conceive of the Uniformity Principle’s being false is independent of the discussion of the circularity of the probabilistic argument for the Uniformity Principle. Even if the probabilistic argument were not circular, we still could conceive of the Principle’s being false in the future.

Update, 17 Jan: I have had second thoughts about the argument in the previous paragraph. Roughly, since the Uniformity Principle is about how things must be, it isn’t clear to me why we must be certain that it is true, as opposed to simply believing it, in order to use reason to draw causal inferences. Again, see the discussion of the Uniformity Principle.

So what is the argument about the circularity of probabilistic arguments for the Uniformity Principle doing there? Again, why did he think he had to make it?

One possibility, which handles both oddities, is that Hume was interested in more than explaining how we make causal inferences. That is, he was interested in questions about our justification for making causal inferences as well as questions about the explanation of our doing so. So, maybe he threw in the argument about circularity in order to show that we are never justified in making any causal inferences.

Next time, I will start with that possibility and then note something that is odd: he seems to say that some of our causal inferences are justified. Oy!


One problem with saying that belief consists in having a forceful idea is that it leaves us unable to explain the difference between believing something and denying it.

The particular example I gave was of two people disagreeing about whether God exists. But, as David pointed out to me, this can be confusing since one way of denying that God exists is to say that God is unintelligible, that is, to deny that we have any idea of God at all. That wasn’t what I had in mind here, but we can avoid the issue entirely by using a different example.

Picture of Cobb Gate If you believe there is a dragon on Cobb Gate, you have a forceful idea of a gargoyle of a dragon on Cobb Gate. It probably looks something like this.

But if I disagree, what is my idea? A forceless idea of a gargoyle of a dragon on Cobb Gate? That’s what one would expect from a theory that puts ideas on a spectrum, with the more forceful ones representing the way things are and the less forceful ones being merely imagined. But that doesn’t make any sense here: there is something that I believe, namely, that there isn’t a dragon on Cobb Gate.

A better way of handling disagreement?

Perhaps my idea is an idea of Cobb Gate without a dragon on it. We can compare the two ideas by the relation of contrariety to see that they are incompatible with one another and that’s what the disagreement consists in. (Nimrod or anyone else: can we photoshop the dragon out? Here’s the original.)

Hmm. I don’t think that is Hume’s story. The way he describes it, two people having a disagreement have the same idea: see But maybe he shouldn’t have said that; maybe we have stumbled on a better story.

Would there be another problem, namely, we can disagree without my having a contrary idea to yours? For example, maybe I don’t have any idea of what Cobb Gate looks like. Maybe I disagree because someone told me there are no gargoyles of dragons on the University of Chicago campus. If so, I might disagree despite having no definite idea of what the gate or the campus looks like.

That has to be so, but, of course, accepting it means pretty much giving up on the theory of ideas because it involves saying that I have a thought about the campus of the University of Chicago without having anything like what Hume would call an idea of the campus of the University of Chicago.


I ended with a question: what does Hume think feeling is?

We are putting a lot of effort into keeping track of what he says about reason and reasoning.

But if we want to know what he thinks reason involves, I would think we ought to know more about the basic contrasting case: feeling (see Abstract, paragraph 5, e.g.). That thought hadn’t occurred to me until yesterday morning.

Here’s a start.

Impressions — both sensations and emotions — are feelings. Ideas are used in thinking or reasoning. (That is my interpretation of Abstract, par. 5: note that the wording of that passage leaves open the possibility that the distinctions between impressions/ideas and between feeling/thinking are different from one another).

Feelings are used in (or perhaps are) our assessments of poetry and music.

Belief involves feelings: the feeling of force or liveliness or whatever is what distinguishes belief from mere conceiving. Similarly, memories have a greater force than imaginings.

What do all of those things share in common? Are they felt as, say, tickles are felt? (But there doesn’t seem to be a common feeling like this across all of those things). Is it that they cannot be put into words? (This isn’t a very Hume-ish way of thinking. Also, how are ideas and impressions compared if this is so?)

Feeling and belief

In the case of belief, there is an interesting suggestion that the relevant feeling is identified in terms of its effects on our thoughts and actions. Thus, beliefs “weigh more in thought,” have “superior influence on passions and imagination,” and are “the governing principles of all our actions.” (; see also

Merely imagined ideas, by contrast, don’t have these effects: I may imagine that I can fly, but I don’t hop off the roof thinking that I will just fly home. I would do that only if I mistakenly believe that I can fly.

That is an interesting set of observations and, if followed up, they might lead in a useful direction.

Still, that isn’t Hume’s official story. His official story is that there is a distinctive, noticeable feel to belief. The difference between belief and other states of mind, such as remembering and imagining, consists in the strength of this feeling. Remembering has the same kind of feeling as belief but it is less strong. Imagining has an even less strong feeling than memory.

Knowledge and feeling

We can know what column A relations ideas have to one another. Those relations are the objects of knowledge and certainty. We cannot imagine the same ideas not being related to one another in just that way (this is the point about the sum of the interior angles of the triangle being equal to the sum of two right angles). (

Belief is different. We believe that cause A will be followed by effect B, but that is not certain. We can imagine that it won’t happen that way.

To believe is to have a forceful idea. To remember is also to have a forceful idea, though it is a little less forceful than a belief caused by a recent impression. To imagine is to have an idea with even less force still.

In other words, as one’s confidence that an idea represents things as they really are goes down, so does the force of the idea.

OK, now what about knowledge? What is the feeling associated with that? I can’t recall Hume saying anything about that. Shouldn’t it be the most forceful of all? There would be a problem with saying that. We gain knowledge by comparing ideas. There would not be an impression to give force and vivacity to my knowledge that the sum of these angles is equal to the sum of those angles. Beliefs, by contrast, get their force and vivacity from impressions.

Humph. We seem to have two questions.

  1. What is the characteristic feeling of knowledge?
  2. How is it related to the characteristic feelings of belief and memory?

Here is a proposal; I am not certain about it, but it strikes me as promising. Knowledge is characterized by our inability to conceive of the denial of what we know. I cannot imagine those two sums being unequal. If I tried, I would fail. So the characteristic feeling of knowledge is a feeling of compulsion or constraint: the inability to think otherwise.

Thus, the person who assents to propositions proved by intuition or demonstration “is necessarily determined to conceive them [the propositions] in that particular manner … whatever is absurd is unintelligible; nor is it possible for the imagination to conveive any thing contrary to a demonstration” ( [Is “that particular manner” assent? mjg]

This puts knowledge close to belief on the spectrum of feeling because the feeling of belief is also a feeling of constraint and inability. Specifically, I cannot believe at will. I can imagine that what I believe is not true, but I cannot induce belief at will. I can imagine that I can fly at will, but I cannot make myself believe that I can fly at will.

The feeling of constraint or inability is stronger in the case of knowledge than it is in the case of belief because I cannot even imagine that what I know is not true whereas I can imagine that what I believe is not true.