Pirates & Revolutionaries: Hume, A Treatise of Human Nature, Book 1, Part 3, Sect 15 Rules by Which to Judge of Causes and Effects, §§369-380

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 XV: Rules by Which to Judge of Causes and Effects

§369 Promiscuous Causality

We have seen already that

a) there are no qualities in object that imply a causal relation to other objects, and

b) there are no qualities that tell us an object has no causal relations whatseover.

Any thing may produce any thing. Creation, annihilation, motion, reason, volition; all these may arise from one another, or from any other object we can imagine. (173b)

This fact follows from two principles we already discussed:

1) the constant conjunction of objects determines their causation, and

2) no objects are contrary to each other unless one exists and the other does not.

And when both objects exist, there is never any reason they cannot be constantly conjoined as cause and effect.

§370 Rules for Unruly Relations

So it is possible for any object to be cause or effect to any other object. Hume will now offer some general rules that will help us know when objects really are causally related.

§371 Causal Contiguity

Rule 1: The cause and effect must be contiguous in space and time

§372 Causal Priority

Rule 2: The cause must be prior to the effect.

§373 Causal Constancy of Connection

Rule 3: Cause and effect must be constantly united. This quality is largely what makes a causal relation.

§374 Similarity and Induction

Rule 4: The same cause always produces the same effect. And, the same effect arises only from the same cause.

Experience teaches us this rule.

Sometimes philosophers or scientists discover a causal relation by means of a clear experiment. They then immediately extend the observation to every phenomenon of the same kind "without waiting for that constant repetition, from which the first idea of this relation is derived." (173-174)

Hence, this rule is also "the source of most of our philosophical reasonings." (173d)

§375 Different Causes for One Effect Share Some Common Quality

Rule 5: In some cases, many different objects produce the same effect. If so, all the causes must share some common quality that is causally linked to the effect.

§376 Hidden Causes Explain Unexpected Effects

Rule 6: When two resembling causes produce unlike effects, there must be some difference between them that has not yet been uncovered.

§377 Graduated Causes

Rule 7: The tighter we compress the spring, the more it presses back on us. If we apply only a small portion of pressure, it will resist with only a small amount of force.

When any object encreases or diminishes with the encrease or diminution of its cause, 'tis to be regarded as a compounded effect, deriv'd from the union of the several different effects, which arise from the several different parts of the cause. The absence or presence of one part of the cause is here suppos'd to be always attended with the absence or presence of a proportionable part of the effect. This constant conjunction sufficiently proves, that the one part is the cause of the other. (174c)

But consider that when we increase the warmth of a room, it might become more pleasant. But if we increase it too much, it might then become unpleasant. So we must only come to such a conclusion after an adequate number of experiments.

§378 Causes that Need Help

One previous example that we suggested was striking a match. The strike caused the flame. But technically it could be that we can only speak of objects. So there is the match. And there is the flame. Matches do not spontaneously light. So the cause can exist without its effect. But when another influence is added, the striking motion, the effect results.

an object, which exists for any time in its full perfection without any effect, is not the sole cause of that effect, but requires to be assisted by some other principle, which may forward its influence and operation. For as like effects necessarily follow from like causes, and in a contiguous time and place, their separation for a moment shews, that these causes are not compleat ones. (174-175)

§379 We will Arrive at Truth through Diligent Experimentation

Hume will now explain the sort of logic that follows from his system.

We find that nature is complex. Often we want to know what is causing something. But first we have to eliminate many competing possibilities.

There is no phaenomenon in nature, but what is compounded and modify'd by so many different circumstances, that in order to arrive at the decisive point, we must carefully separate whatever is superfluous, and enquire by new experiments, if every particular circumstance of the first experiment was essential to it. These new experiments are liable to a discussion of the same kind; so that the utmost constancy is requir'd to make us persevere in our enquiry, and the utmost sagacity to choose the right way among so many that present themselves. (175c)

So this is a major problem in natural philosophy. But matters are even more complex in moral philosophy

where there is a much greater complication of circumstances, and where those views and sentiments, which are essential to any action of the mind, are so implicit and obscure, that they often escape our strictest attention, and are not only unaccountable in their causes, but even unknown in their existence. (175c.d)

§380 We should Broaden Our Inquiry to Brutes

To obtain more assurances of Hume's system, he should broaden the experiments. This is why he will examine animal (and human) reasoning in the next section.

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From the original text:

Sect. xv. Rules by Which to Judge of Causes and Effects.
According to the precedent doctrine, there are no objects which by the mere survey, without consulting experience, we can determine to be the causes of any other; and no objects, which we can certainly determine in the same manner not to be the causes. Any thing may produce any thing. Creation, annihilation, motion, reason, volition; all these may arise from one another, or from any other object we can imagine. Nor will this appear strange, if we compare two principles explained above, THAT THE CONSTANT CONJUNCTION OF OBJECTS DETERMINES THEIR CAUSATION, AND [Part I. Sect. 5.] THAT, PROPERTY SPEAKING, NO OBJECTS ARE CONTRARY TO EACH OTHER BUT EXISTENCE AND NON-EXISTENCE. Where objects are not contrary, nothing hinders them from having that constant conjunction, on which the relation of cause and effect totally depends.
Since therefore it is possible for all objects to become causes or effects to each other, it may be proper to fix some general rules, by which we may know when they really are so.
(1) The cause and effect must be contiguous in space and time.
(2) The cause must be prior to the effect.
(3) There must be a constant union betwixt the cause and effect. It is chiefly this quality, that constitutes the relation.
(4) The same cause always produces the same effect, and the same effect never arises but from the same cause. This principle we derive from experience, and is the source of most of our philosophical reasonings. For when by any clear experiment we have discovered the causes or effects of any phaenomenon, we immediately extend our observation to every phenomenon of the same kind, without waiting for that constant repetition, from which the first idea of this relation is derived.
(5) There is another principle, which hangs upon this, viz. that where several different objects produce the same effect, it must be by means of some quality, which we discover to be common amongst them. For as like effects imply like causes, we must always ascribe the causation to the circumstance, wherein we discover the resemblance.
(6) The following principle is founded on the same reason. The difference in the effects of two resembling objects must proceed from that particular, in which they differ. For as like causes always produce like effects, when in any instance we find our expectation to be disappointed, we must conclude that this irregularity proceeds from some difference in the causes.
(7) When any object encreases or diminishes with the encrease or diminution of its cause, it is to be regarded as a compounded effect, derived from the union of the several different effects, which arise from the several different parts of the cause. The absence or presence of one part of the cause is here supposed to be always attended with the absence or presence of a proportionable part of the effect. This constant conjunction sufficiently proves, that the one part is the cause of the other. We must, however, beware not to draw such a conclusion from a few experiments. A certain degree of heat gives pleasure; if you diminish that heat, the pleasure diminishes; but it does not follow, that if you augment it beyond a certain degree, the pleasure will likewise augment; for we find that it degenerates into pain.
(8) The eighth and last rule I shall take notice of is, that an object, which exists for any time in its full perfection without any effect, is not the sole cause of that effect, but requires to be assisted by some other principle, which may forward its influence and operation. For as like effects necessarily follow from like causes, and in a contiguous time and place, their separation for a moment shews, that these causes are not compleat ones.
Here is all the LOGIC I think proper to employ in my reasoning; and perhaps even this was not very necessary, but might have been supplyd by the natural principles of our understanding. Our scholastic head-pieces and logicians shew no such superiority above the mere vulgar in their reason and ability, as to give us any inclination to imitate them in delivering a long system of rules and precepts to direct our judgment, in philosophy. All the rules of this nature are very easy in their invention, but extremely difficult in their application; and even experimental philosophy, which seems the most natural and simple of any, requires the utmost stretch of human judgment. There is no phaenomenon in nature, but what is compounded and modifyd by so many different circumstances, that in order to arrive at the decisive point, we must carefully separate whatever is superfluous, and enquire by new experiments, if every particular circumstance of the first experiment was essential to it. These new experiments are liable to a discussion of the same kind; so that the utmost constancy is requird to make us persevere in our enquiry, and the utmost sagacity to choose the right way among so many that present themselves. If this be the case even in natural philosophy, how much more in moral, where there is a much greater complication of circumstances, and where those views and sentiments, which are essential to any action of the mind, are so implicit and obscure, that they often escape our strictest attention, and are not only unaccountable in their causes, but even unknown in their existence? I am much afraid lest the small success I meet with in my enquiries will make this observation bear the air of an apology rather than of boasting.
If any thing can give me security in this particular, it will be the enlarging of the sphere of my experiments as much as possible; for which reason it may be proper in this place to examine the reasoning faculty of brutes, as well as that of human creatures.