Probability and the Idea of Cause and Effectby David Hume
Knowledge is Based on Four Relations, Reason and Understanding is Based on One Relation: Causation
Those 4 relations of resemblance, contrariety, quality, and quantity are the foundation of science.
The other 3 relations do not depend on the idea.
They may be absent or present even while the idea remains the same.
These 3 relations are:
- The situations in time and place
All kinds of reasoning consist in a comparison and discovery of those relations, whether constant or inconstant, between objects.
We may make this comparison when:
- those objects are present to the senses,
- neither objects are present, or
- only one object is present.
When both the objects are present to the senses, along with the relation, we call this ‘perception’ rather than reasoning.
In this case, the thought does no action.
There is a mere passive admission of the impressions through the senses.
According to this way of thinking, we should not receive as reasoning any of the observations that we make on identity and time and place, since the mind in these cannot go beyond what is present to the senses to discover the real existence or the relations of objects. Only causation produces such a connection that gives us an assurance, from the existence or action of one object, that it was followed or preceded by any other existence or action.
Nor can identity or time and place be used in reasoning, except so far as they affect or are affected by causation.
There is nothing in any objects to persuade us that they are always remote or always contiguous.
If from experience, we discover that their remoteness or contiguity is invariable, we always conclude that there is some secret cause which separates or unites them.
The same reasoning extends to identity.
- suppose an object may continue individually the same, though several times absent from and present to the senses, and
- ascribe to an object an identity, despite the interruption of the perception, whenever we conclude that if we had kept our eye or hand
- constantly on it, it would have conveyed an invariable and uninterrupted perception.
But this conclusion beyond the impressions of our senses can be founded only on the connection of cause and effect.
We cannot otherwise have any security that the object is not changed upon us, no matter how much the new object may resemble the object which was formerly present to the senses.
Whenever we discover such a perfect resemblance, we consider whether:
- it is common in that species of objects, and
- any cause could operate in producing the change and resemblance.
We create our judgment on the identity of the object according to our determination of these causes and effects.
Causation is the only relation of those three, that:
- do not depend on the mere ideas,
- can be traced beyond our senses,
- informs us of existences and objects that we do not see nor feel.
We will consider the origin and idea of causation.
It is impossible to:
- reason justly, without understanding perfectly the idea on which we reason, and
- understand any idea, without:
- tracing it up to its origin, and
- examining that primary impression from which it arises.
The examination of the impression bestows a clearness on the idea.
The examination of the idea bestows a like clearness on all our reasoning. Let us view two objects, which we call cause and effect.
Cause and Effect
Let us turn them on all sides to find the impression that produces an idea of such consequence.
Initially, I perceive that I must not search for the impression in any of the qualities of the objects, since whatever quality I pitch on, I find that some objects do not have it, and yet are classified as cause or effect.
Everything can be a cause or an effect.
But no quality exists in all things to make them caues or effects universally.
Cause is Defined by Its Contiguity and Succession to Its Effect, and their Consequential Connection
The idea of causation then must be derived from some relation among objects.
Objects that are considered as causes or effects are contiguous. Causes and effects operate and exist in a time or place. Distant objects may sometimes seem to produce each other.
But in reality, they are commonly linked by a chain of causes, contiguous among themselves and to the distant objects. If we cannot discover this connection, we still presume it to exist.
Therefore, contiguity is essential to causation until we can find a more proper occasion (Part 4, Section 5) to clear up this matter by examining which objects are susceptible of juxtaposition and conjunction.
The second relation essential to causes and effects is the priority of time of the cause before the effect.
It is not so universally acknowledged. But it is liable to some controversy.
Some pretend that:
- a cause does not necessarily precede its effect, and
- any object or action, in the very first moment of its existence can produce another object or action, perfectly co-temporary with itself.
But that experience in most instances seems to contradict this opinion.
We may establish the relation of priority by a kind of inference or reasoning. It is an established maxim in natural and moral philosophy, that an object which exists for any time in its full perfection without producing another, is not its sole cause.
It is assisted by some other principle which: pushes it from its state of inactivity, and makes it exert that energy which it secretly had. According to this maxim, if any cause exists at the same time as its effect, then all causes must exist at the same time as all effects, since any one cause which stops its causation for a single moment stops being a cause.
This would lead to:
- the destruction of that succession of causes which we observe in the world, and
- the utter annihilation of time.
Because if one cause happened simultaneously with its effect, and this effect happened simultaneously with its own effect, and so on, then:
- there would be no such thing as succession, and
- all objects would exist at the same time.
After discovering contiguity and succession to be essential to causes and effects, I find I:
- am stopped short, and
- can proceed no further in considering any single example of cause and effect.
Motion Transfer in Bodies
We impulsively think of motion in Body 1 as the cause of motion in Body 2.
When we consider these objects with utmost attention, we find only that: Body 1 approaches Body 2, and The motion of Body 2 comes from Body 1, but without any sensible interval. It is in vain to rack ourselves thinking about this. We can go no further in considering this particular example. If anyone leaves this example and defines cause as something that produces another cause, then he would say nothing.
For what does he mean by ‘produce’? Can he define it, that will not be the same with that of causation? If he cannot, then he runs in a circle. He gives a synonymous term instead of a definition. We should not be content with these two relations of contiguity and succession as affording a complete idea of causation.
An object may be contiguous and prior to another, without being its cause. There is a necessary, consequential connection to be taken into consideration. That relation is much more important than any of the other two above-mentioned. Again, I turn the object on all sides to discover the nature of this consequential connection.
I find the impression, or impressions, from which its idea may be derived. When I view the known qualities of objects, I immediately discover that the relation of cause and effect does not depend on them. I can find only their relations of contiguity and succession. I have already regarded them as imperfect and unsatisfactory. Does this mean that I have an idea which is not preceded by any similar impression? This would be too strong a proof of levity and inconstancy, since the contrary principle has already been established. Instead, we should examine things more fully. Some people who look for something, beat about all the neighbouring fields without any design, hoping their good fortune will guide them.
Therefore, we must proceed like them. We need to: leave the direct survey of this question about the nature of that consequential connection of cause and effect, and try to answer two questions which might give a hint to clear up the present difficulty: Why must everything have a cause? Why should such causes have such effects? What is the nature of: that inference we draw from the one to the other? our belief in that inference? Impressions of reflection
The ideas of cause and effect are derived from:
the ‘impressions of reflection’, and the ‘impressions of sensation’. For brevity, I mention only the impressions of sensation as the origin of these ideas. Though everything that I say of the impressions of sensation also extend to the impressions of reflection. Passions are connected with their objects and with one another, just as external bodies are connected.
The same relation of cause and effect, which belongs to one, must then be common to all of them.