Cause and correlation

Notes for October 17

Main points

This class was about Hume’s positive story about causal inferences. He offered a definition of cause and an explanation of why we draw inferences about cause and effect.

Causal inferences according to Hume

We draw causal inferences, according to Hume, as a matter of habit. After we have seen enough As constantly conjoined with Bs, our minds draw the conclusion that the next A will be followed by a B. This is not a process of reasoning because we cannot explain why the constant conjunction of As and Bs in the past is relevant to the likelihood that an A will be followed by a B in the future. Rather, it is something that we do out of habit.

And we are quite fortunate that our habits of mind seem to work reasonably well at enabling us to get around. That is, we seem to draw inferences that predict what will, in fact, happen pretty well.

Given these observations about how we make causal inferences, Hume offered a definition of a cause. This definition treated three things as equivalent (see p. 51):

  1. A cause is “an object, followed by another, and where all the objects, similar to the first, are followed by objects similar to the second.”

  2. An object is a cause when “if the first object had not been, the second had never existed.”

  3. A cause is “an object followed by another, and whose appearance always conveys the thought to another.”

These all say different things. The first says that causes have to be uniform: A causes B at one point in time only if things like A always cause things like B at any point in time. The second says that causes are necessary conditions of effects. And the third says that causes make us draw conclusions about their effects in our minds. This one seems to me to be incompatible with the other two: it’s about our minds while the others are about objects outside of the mind.

The important thing about these definitions is that Hume has not actually distinguished cause from correlation. Causes make their effects happen. It’s that element of making that, in Hume’s opinion, we cannot ever understand. The most we will ever have, he effectively claims, is ever more precise correlations. We will never understand why one thing makes it necessary that another thing happen. And so we will never really understand why one thing causes another to happen. Hume’s definitions are supposed to express the closest that we can come to understanding cause and effect.

Why did Hume find it interesting?

Why is skepticism about induction interesting? Don’t get me wrong. It’s a nifty problem. But it’s not going to change the way you live and Hume never suggested that it should. So why did he find it so exciting?

In my opinion, it was part of Hume’s project of providing an alternative to a religious idea of our place in the universe. Philosophical rationalists thought that we were made in the image of God and that we should develop our powers of reason in order to achieve the kind of understanding of the universe that, they thought, God possessed. This attitude is clearly expressed in Reverend South’s sermon; it is also there, in more measured tones, at the end of Descartes’s third meditation.

Hume, by contrast, did not think that reason could give us significant insight into either the nature of the world or ethics. The attempt to rely on it would be disastrous for us. He thought we would be better off seeing ourselves as, in his opinion, we really are: one kind of animal among others with no special place in the universe.

Key concepts

  1. Habit as an explanation of why we draw causal inferences. Is it satisfactory?
  2. Hume’s definitions of ‘cause.’
This page was written by Michael Green for Problems of Philosophy, Philosophy 1, Fall 2013. It was posted October 24, 2013.
Problems of Philosophy