David Hume: An Enquiry Concerning Human Understanding

What is causation? What does it mean to say that ‘A causes B’?

Background

David Hume (7 May 1711 – 25 August 1776) was a Scottish enlightenment philosopher, historian, economist, and essayist.

He is best known for his system of philosophical empiricism, skepticism, and naturalism, which challenged the rationalism and innate ideas of his predecessors, by attempting establish a naturalistic science of man.

He wrote influential works such as A Treatise of Human Nature, An Enquiry Concerning Human Understanding, An Enquiry Concerning the Principles of Morals, and Dialogues Concerning Natural Religion.

It is also worth nothing that he expressed racist views on the inferiority of non-white people, especially in his essay Of National Characters, and was involved in the slave trade through his patron and through investments.

What is causation?

If we put some Lithium or other group one element in water, what happens? Would you say that this necessarily must happen? Why?

If someone holds a pen and then lets go of it (so that it is now unsupported) will it fall? Will it necessarily fall? Why?

We seem to have a fairly strong intuition that in each case, one thing will necessarily follow another. Hume thought we were wrong about that.

Hume’s fork

According David Hume, there were two kinds of things that we can know: relations of ideas, or matters of fact

Relations of ideas are known through immediate recognition of relation or intuition (e.g. maths, geometry, all bachelors are unmarried); They are a priori. That is, we don't need experience to know they're true. They are necessarily true.

There is a test for establishing whether something is a relation of ideas:

negate it.
Is it a contradiction in terms?
If so, then it is a relation of ideas.

E.g. Take the proposition 'a triangle has three sides'. If we negate it we get, 'A triangle does not have three sides', which is clearly a contradiction in terms. So we can conlcude that this idea is a relation of ideas.

Matters of fact are known through immediate perception: They are inferred through judgements of probability; They are synthetic and a posteriori; They are probably true

All the objects of human reason or enquiry may naturally be divided into two kinds, to wit, Relations of Ideas, and Matters of Fact. Of the first kind are the sciences of Geometry, Algebra, and Arithmetic; and in short, every affirmation which is either intuitively or demonstratively certain. That the square of the hypothenuse is equal to the square of the two sides, is a proposition which expresses a relation between these figures. That three times five is equal to the half of thirty, expresses a relation between these numbers. Propositions of this kind are discoverable by the mere operation of thought, without dependence on what is anywhere existent in the universe. Though there never were a circle or triangle in nature, the truths demonstrated by Euclid would for ever retain their certainty and evidence.

Matters of fact, which are the second objects of human reason, are not ascertained in the same manner; nor is our evidence of their truth, however great, of a like nature with the foregoing. The contrary of every matter of fact is still possible; because it can never imply a contradiction, and is conceived by the mind with the same facility and distinctness, as if ever so conformable to reality. That the sun will not rise to-morrow is no less intelligible a proposition, and implies no more contradiction than the affirmation, that it will rise. We should in vain, therefore, attempt to demonstrate its falsehood. Were it demonstratively false, it would imply a contradiction, and could never be distinctly conceived by the mind.

-Hume’s Enquiry Concerning Human Understanding Section IV, part I

The problem of induction

Perhaps the most shattering of Hume's arguments was his attack on the problem of induction.

Induction is the process by which we establish that one thing follows (or is caused by) another. We see that B follows A every time, and so assume that the same will occur in the future. This is called the Uniformity Principle:

If ‘I have found that such and such an object has always had such and such an effect’, then ‘I foresee that other objects which appear similar will have similar effects’.

However, what is the basis for such a claim?

Can you see where Hume is going?

How could he apply his Fork to the Uniformity Principle? Is the Uniformity Principle a Relation of Ideas or a Matter of Fact?

Is the Uniformity Principle a relation of ideas? No, because if we negate the Uniformity Principle, we don't end up with a contradiction.

Is the Uniformity Principle a matter of fact? No, because any argument for the Uniformity Principle based on observation, will presupposed the Uniformity Principle.

So what is the Uniformity Principle then? Can we know it at all?

Hume concludes that there is no basis for thinking that, just because B has always followed A, B will follow A next time. He believes that our belief in causation is nothing but custom.

After the constant conjunction of two objects—heat and flame, for instance, or weight and solidity—sheer habit makes us expect the one when we experience the other. Indeed, this hypothesis seems to be the only one that could explain why we draw from a thousand instances an inference which we can’t draw from a single one that is exactly like each of the thousand. •Reason isn’t like that. The conclusions it draws from considering one circle are the same as it would form after surveying all the circles in the universe. But no man, having seen only one body move after being pushed by another, could infer that every other body will move after a similar collision. All inferences from experience, therefore, are effects of custom and not of •reasoning.

…the supposed tie or connexion between the cause and effect, which binds them together, and renders it impossible, that any other effect could result from the operation of that cause that after a repetition of similar instance, the mind is carried by habit [custom], upon the appearance of one event, to expect its usual attendant, and to believe that it will exist. This connexion, therefore, which we feel in the mind, this customary transition of the imagination from one object to its usual attendant, is the sentiment or impression, from which we form the idea of power or necessary connexion.

…

Custom, then, is the great guide of human life. It is that principle alone which renders our experience useful to us, and makes us expect, for the future, a similar train of events with those which have appeared in the past. Without the influence of custom, we should be entirely ignorant of every matter of fact beyond what is immediately present to the memory and senses. We should never know how to adjust means to ends, or to employ our natural powers in the production of any effect. There would be an end at once of all action, as well as of the chief part of speculation.

-David Hume, An Enquiry Concerning Human Understanding

Discussion

But surely it is necessary that Lithium will react with water. It seems absurd to suggest that the connection between cause and effect here is no stronger than our custom of, for example, wearing ties. Would the shock we might feel upon seeing an unsupported pen float in the air after we dropped it be the same as the shock we might feel if someone was wandering around naked?

Secondly, Hume had his own counter-example to his Fork.

Hume thought that perceptions are either impressions or ideas and this is how we come to know Matters of Fact. However, if ideas are copies of impressions, then if we have never experienced X, we can have no idea of X. But look at the diagram below. We have not experienced the ‘missing-shade-of blue’ … yet can have an idea of it. This missing shade of blue can't be a Matter of Fact and how can it be a Relation of Ideas?

Tasks

Explain Hume's Fork.
Explain Hume’s argument against induction and his conclusion that ‘custom is the great guide of human life’.
Provide one objection to Hume's view.
Do you agree with Hume? Is causation nothing but custom?

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