Pirates & Revolutionaries: Hume, A Treatise of Human Nature, Book 1, Part 3, Sect 4 " Of the Component Parts of Our Reasonings Concerning Cause and Effect" §§193-195

by Corry Shores
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[The following is summary, up to the end where I reproduce this section in full. My commentary is in brackets. Paragraph headings are my own.]

David Hume

A Treatise of Human Nature

Book I: Of the Understanding

Part III: Of Knowledge and Probability

Section IV: Of the Component Parts of Our Reasonings Concerning Cause and Effect.

§193 Inferring Causation

[We have the idea of an apple. This came first from seeing one. After eating an apple, we felt nourished. In fact, it seems every time we have ever eaten an apple, it was followed immediately with this feeling of nourishment. Hence, we come to infer that the feeling of nourishment results from the apple. In other words, we infer the effect from the cause. But there is no quality in apples, nor in the feeling of nourishment, that suggest the two necessarily must be related causally. So in a sense, our inference goes beyond what is given to our senses, and concludes something about the ideas that the sense impressions produce.]

We originally have impressions of objects. The ideas of these impressions can become related as causes and effects. The mind then reasons based on these ideas. And in a way it goes beyond these objects that it sees or remembers. Nonetheless, while it is reasoning, the mind must always keep in sight some impressions. This means that its ideas must have some impressional content mixed-in.

[Now imagine it is St. Patrick's Day. You began celebrating early in the day. You nap. Then you awake and arise somehow feeling nourished, in the way that apples make you feel. You have no memories of what happened before falling asleep. However, you notice an apple-core on the table. You still attribute the feeling of nourishment to eating the apple. But this time it is the idea of an apple you consider as the cause, rather than a sense impression of actually eating it. However, some sense impression must somehow be mixed-in. Seeing the apple core, you related it to all those times you ate an apple and left the core. Thus we make an inference from the core we now see: we must have eaten an apple before sleeping. If the causes are not sensibly apparent, there is at least a chain of causation leading to a sense impression, when we infer causal relations.]

So when we infer effects from causes, we must establish the causes' existence. We have two ways to do so:

1) we immediately perceive the cause in our senses or memory. Or,

2) we infer the cause from inferences of other prior causes. Then either

2a) we immediately perceive this prior cause in our senses or memory, or

2b) we infer this prior cause from an even more prior cause. This regression must eventually terminate in some sense impression.

It is impossible for us to carry on our inferences in infinitum; and the only thing, that can stop them, is an impression of the memory or senses, beyond which there is no room for doubt or enquiry. (83a)

§194 Causing the Rubicon

To illustrate, Hume shows how this process happens in historical accounts. We begin by choosing some event in history. Then we consider the reasons that we believe it happened, or doubt that it occurred. So for example, we believe that Caesar was murdered at the senate-house on the 'ides of March.' Most historians agree that in fact this particular event happened on that day.

Now, we have the idea of this event. We learned it from books. So we also recall the letter-characters of the words we had read when we first learned this fact. These words were used as signs for certain ideas that the history book writers used to explain this event.

Now, the idea of this event was originally obtained by people witnessing it first-hand. Then, the account of the occurrence was conveyed to a first generation of historians. By that means it was conveyed to a second generation of historians. And so on until the idea of the event was conveyed to the history book writer who taught us this historical fact.

So, the ideas that we have of events in the past either come from our own sense impressions, or from the sense impressions of someone else. This other person's ideas were then conveyed from person to person until finally arriving to our minds.

Hume considers each act of conveyance as a causal relation. One historian causes the next historian to grasp the idea of the event. The conveyed idea is the effect of that cause. So when we consider the idea in our minds, we regard it as an effect. Its chain of causation however terminates in someone's sense impressions.

If the chain of conveyance/causation never terminated in some sense impressions, then "our whole reasoning wou'd be chimerical and without foundation." For,

every link of the chain wou'd in that case hang upon another; but there wou'd not be any thing fix'd to one end of it, capable of sustaining the whole; and consequently there wou'd be no belief nor evidence. (83d)

For comparison, consider when we argue hypothetically or reason upon supposition, such as Samuel Clarke's argumentation for the claim that all things must have a cause [see §188]. He proves it by forming a reductio argument based on a hypothetical supposition of the counter claim:

Suppose that nothing causes some thing.

But, if nothing causes some thing, then it must be the cause of itself. Hence whether something causes it or not, either way it is caused.

We notice the "if" portion of such hypothetical arguments. But the if-clause is something that only possibly can be fulfilled by sensation. In this case, we are supposing if we do not have enough evidence to conclude that nothing causes a thing. But we have not experienced the sense impressions yet which would allow us to come to that conclusion. Yet we do not care anyway, because we are showing that it does not matter whether or not we obtain that evidence. Hume's point is that such suppositions or hypothetical arguments do not terminate in some present impression or in some belief in a real existence. Hence in that way they are "chimerical and without foundation."

§195 Reasoning is Always Firstly Sensation

Some still might argue that we may reason without recourse to sense impressions. [They might offer as an example that we first conclude that apples make us feel nourished. Then we retain this idea of the apple's nourishment. Our experiences also teach us that bananas make us feel nourished too. Then we retain that idea as well. Later, we decide that we will make a nourishing fruit salad. We combine the idea of the apple's nourishment with the idea of the banana's nourishment. By means of this combination of just ideas alone, we conclude that a salad made of apples and bananas will be highly nourishing.]

Hume even grants that the original memories of the sense impressions could be completely erased from our memories. However, he argues that there still remains the conviction we have regarding the impression. [So we might remember our certainty that apples and bananas are nourishing, even though we can no longer recall ever eating those fruits.] So no matter what, our "abstract" reasoning is always grounded-in and originated-from concrete sense experiences. (84ab)

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From the original text:

Sect. iv. Of the Component Parts of Our Reasonings Concerning Cause and Effect.
Though the mind in its reasonings from causes or effects carries its view beyond those objects, which it sees or remembers, it must never lose sight of them entirely, nor reason merely upon its own ideas, without some mixture of impressions, or at least of ideas of the memory, which are equivalent to impressions. When we infer effects from causes, we must establish the existence of these causes; which we have only two ways of doing, either by an immediate perception of our memory or senses, or by an inference from other causes; which causes again we must ascertain in the same manner, either by a present impression, or by an inference from their causes, and so on, till we arrive at some object, which we see or remember. It is impossible for us to carry on our inferences IN INFINITUM; and the only thing, that can stop them, is an impression of the memory or senses, beyond which there is no room for doubt or enquiry.
To give an instance of this, we may chuse any point of history, and consider for what reason we either believe or reject it. Thus we believe that Caesar was killed in the senate-house on the ides of March; and that because this fact is established on the unanimous testimony of historians, who agree to assign this precise time and place to that event. Here are certain characters and letters present either to our memory or senses; which characters we likewise remember to have been used as the signs of certain ideas; and these ideas were either in the minds of such as were immediately present at that action, and received the ideas directly from its existence; or they were derived from the testimony of others, and that again from another testimony, by a visible gradation, it will we arrive at those who were eyewitnesses and spectators of the event. It is obvious all this chain of argument or connexion of causes and effects, is at first founded on those characters or letters, which are seen or remembered, and that without the authority either of the memory or senses our whole reasoning would be chimerical and without foundation. Every link of the chain would in that case hang upon another; but there would not be any thing fixed to one end of it, capable of sustaining the whole; and consequently there would be no belief nor evidence. And this actually is the case with all hypothetical arguments, or reasonings upon a supposition; there being in them, neither any present impression, nor belief of a real existence,
I need not observe, that it is no just objection to the present doctrine, that we can reason upon our past conclusions or principles, without having recourse to those impressions, from which they first arose. For even supposing these impressions should be entirely effaced from the memory, the conviction they produced may still remain; and it is equally true, that all reasonings concerning causes and effects are originally derived from some impression; in the same manner, as the assurance of a demonstration proceeds always from a comparison of ideas, though it may continue after the comparison is forgot.