Section 6

The Inference from the Impression to the Idea

by David Hume Icon

The Constant Conjunction Between Cause and Effect Comes from Experience

The inference we draw from cause to effect is not derived merely from:

  • a survey of these particular objects, and
  • a penetration into the essences of such objects to discover the dependence of one objects on the other.

No object implies the existence of any other object if we:

  • consider these objects in themselves, and
  • never look beyond the ideas which we form of them.

Such an inference would:

  • amount to knowledge, and
  • imply the absolute contradiction and impossibility of conceiving anything different.

But as all distinct ideas are separable, there can be no impossibility of that kind.

When we pass from a present impression to the idea of any object, we might:

  • separate the idea from the impression, and
  • substitute any other idea in its room.

Therefore, it is by experience only, that we can infer the existence of one object from that of another object.

The nature of experience is that we remember:

  • to have had frequent instances of the existence of one species of objects, and
  • that the other species of objects have:
    • always attended them, and
    • existed in a regular order of contiguity and succession with regard to them.

We remember to have seen a flame.

We have felt that sensation we call heat.

We likewise call to mind their constant conjunction in all past instances.

Without any further ceremony, we:

  • call the one cause and the other effect, and
  • infer the existence of the one from that of the other.

In all those instances where we learn the conjunction of particular causes and effects, both the causes and effects:

  • have been perceived by the senses, and
  • are remembered.

But in all cases, when we reason on causes and effects, only one is perceived or remembered.

The other is supplied in conformity to our past experience.

Thus in advancing, we have insensibly discovered a new relation between cause and effect, when we:

  • least expected it, and
  • were examining another subject.

This relation is their constant conjunction.

Contiguity and succession are not enough to make us declare any two objects to be cause and effect, unless we perceive that these two relations are preserved in several instances.

We can now see the advantage of quitting the direct survey of this relation, to discover the nature of that necessary connection which makes so essential a part of it.

We hope that through this, we can arrive at our proposed end. But honestly, this newly discovered relation of a constant conjunction seems to advance us very little, because it only implies that like objects have always been placed in like relations of contiguity and succession. This means that we can: never discover any new idea, and only multiply, but not enlarge the objects of our mind. What we do not learn from one object, we can never learn from 100 of the same kind.

Our senses show us in one instance two bodies, motions, or qualities in certain relations of success and contiguity. Our memory presents us only with a multitude of instances. We always find like bodies, motions, or qualities in like relations in these instances. From the mere repetition of any past impression, even to infinity, there never will arise any new original idea, such as that of a necessary connection. The number of impressions has in this case no more effect than if we confined ourselves to one only. This reasoning seems just and obvious.

But we will continue this examination, as it would be folly to despair too soon. Having found, that after the discovery of the constant conjunction of any objects, we always draw an inference from one object to another, we shall now examine: the nature of that inference, and the transition from the impression to the idea. Perhaps ultimately, the necessary connection depends on the inference instead of the inference’s depending on the necessary connection.

The transition from an impression in the memory or senses to an idea, which is either a cause or effect, is founded on:

  • past experience, and
  • on our remembrance of their constant conjunction.

The next question is:

  • does experience produce the idea via the understanding or imagination, and
  • do we make the transition:
    • by reason, or
    • a certain association of perceptions?

If reason made us to the transition, it would be caused by the principle, that:

  • instances that we had no experience of must resemble those that we have had experience, and
  • the course of nature is always uniformly the same.

To clear up this matter, let us consider all the arguments on which such a proposition may be founded.

As these must be derived from knowledge or probability, let us view each of these degrees of evidence and see whether they afford any just conclusion of this nature.

Our foregoing method of reasoning will easily convince us that no demonstrative arguments can prove that those instances, of which we have had no experience, resemble those, of which we have had experience.

We can at least conceive a change in the course of nature.

This proves that such a change is not absolutely impossible.

To form a clear idea of anything, is:

  • an undeniable argument for its possibility, and
  • alone a refutation of any pretended demonstration against it.

Probability only discovers the relations of objects, not the relations of ideas.

It must be founded in some respects on:

  • the impressions of our memory and senses, and
  • our ideas.

If there were no mixture of any impression in our probable reasonings, the conclusion would be entirely chimerical.

If there were no mixture of ideas, the mind’s action in observing the relation would be sensation, not reasoning. In all probable reasonings there must therefore be something present to the mind, either seen or remembered.

From this, we infer something connected with it which is not seen nor remembered.

Only cause and effect is the relation of objects which can lead us beyond the immediate impressions of our memory and senses because it is the only connection on which we can found a just inference from one object to another.

The idea of cause and effect is derived from experience.

Experience informs us that such objects in all past instances, have been constantly conjoined with each other. An object similar to one of these objects is supposed to be immediately present in the impression in our experience.

This makes us presume the existence of an object similar to its usual attendant object.

According to this, probability is founded on the presumption of a resemblance between:

  • those objects we have experienced, and
  • those objects which we have had no experience.

Therefore, our presumption on an existence of a cause or effect can never arise from probability.

The same principle cannot be both the cause and effect of another.

This is perhaps the only proposition concerning that cause and effect, that is intuitively or demonstratively certain.

Anyone who eludes this argument without determining whether our reasoning on cause and effect is derived from demonstration or probability, pretends that all conclusions from causes and effects are built on solid reasoning.

This reasoning should be produced for us to examine it.

After the experience of the constant conjunction of certain objects, we reason in the following manner:

Such an object is always found to produce another object. It could not have this effect if it did not have a power of production. The power necessarily implies the effect.

Therefore, there is a just foundation for drawing a conclusion from the existence of one object to that of its usual attendant.

The past production implies a power.

The power implies a new production. The new production is what we infer from the power and the past production.

It would be easy for me to show the weakness of this reasoning through:

  • observing:
  • that the idea of production is the same with the idea of causation, and
  • that no existence certainly and demonstratively implies a power in any other object, or
  • the idea we form of power and efficacy.

But doing so would weaken my system by:

  • resting one part of it on another, or
  • breeding a confusion in my reasoning.

Thus, I shall try to maintain my present assertion without any such assistance.

For now, we allow that:

  • the production of one object by another in any one instance implies a power, and
  • this power is connected with its effect.

It has been already proven that:

  • the power does not lie in the sensible qualities of the cause, and
  • only the sensible qualities are present to us.

Why do you presume in other instances that the same power still exists, merely on the appearance of these qualities?

Your appeal to past experience decides nothing in the present case.

It can only prove that that very object, which produced any other, was at that very instant endowed with such a power.

But it can never prove that the same power must continue in the:

  • same object, or
  • collection of sensible qualities.

I can much less prove that a like power is always conjoined with like sensible qualities if:

  • the same power continues united with the same object, and
  • like objects are endowed with like powers.

In this case, I ask: why from this experience we form any conclusion beyond those past instances which we experienced.

If you answer this question in the same way as the preceding question, your answer creates a new question to infinity.

This clearly proves that the foregoing reasoning is baseless. Reason Cannot Explain the Connection of Cause and Effect Because that Connection is Based on Impressions Our reason fails to discover the ultimate connection of causes and effects.

Even after experience has informed us of their constant conjunction, it is impossible for us to satisfy ourselves why we should extend that experience beyond those particular instances we have observed.

We suppose, but are never able to prove, that there must be a resemblance between those objects:

  • of which we have had experience, and
  • which lie beyond our discovery.

We have already noticed relations which make us pass from one object to another.

Even though there is no reason to determine us to that transition. We may establish this for a general rule that wherever the mind constantly and uniformly makes a transition without any reason, it is influenced by these relations.

This is exactly the present case.

Reason can never show us the connection of one object with another, though aided by:

  • experience, and
  • the observation of their constant conjunction in all past instances.

When the mind passes from the idea or impression of one object to the idea or belief of another, it is not determined by reason.

It is determined by certain principles which:

  • associate the ideas of these objects, and
  • unite them in the imagination.

Had ideas no more union in the fancy than objects seem to have to the understanding, we could never:

  • draw any inference from causes to effects, and
  • rest belief in any matter of fact.

The inference, therefore, depends solely on the union of ideas.

The principles of union among ideas, I have reduced to three general ones. I have asserted that the idea or impression of any object naturally introduces the idea of any other object, that is resembling, contiguous to, or connected with it.

These principles are not the infallible nor the sole causes of an union among ideas.

They are not the infallible causes because one may fix his attention for some time on any one object without looking farther.

They are not the sole causes because the thought:

  • has a very irregular motion in running along its objects, and
  • may leap from the heavens to the earth, from one end of the creation to the other, without any method or order.

I allow:

  • this weakness in these three relations, and
  • this irregularity in the imagination.

Yet I assert that the only general principles which associate ideas are:

  • resemblance,
  • contiguity,
  • causation.

There is a principle of union among ideas.

At first sight, it may be different from any of these.

But it ultimately depends on the same origin.

When every individual of any species of objects is found to be constantly united with an individual of another species, the appearance of any new individual of species naturally conveys the thought to its usual attendant.

Thus, because such an idea is commonly annexed to such a word, only hearing that word is needed to produce the correspondent idea.

It will be impossible for the mind to prevent that transition.

In this case, it is not absolutely necessary that on hearing such a sound, we should:

  • reflect on any past experience
  • consider what idea has been usually connected with the sound.

The imagination itself supplies the place of this reflection.

It is so accustomed to pass from the word to the idea, that it does not interpose a moment’s delay between:

  • the hearing of the one
  • the conception of the other.

This is a true principle of association among ideas.

But I assert it to be:

  • the very same with the principle between the ideas of cause and effects, and
  • an essential part in all our reasonings from that relation.

We have no other notion of cause and effect, but that of certain objects which have been:

  • always conjoined together, and
  • found inseparable in all past instances.

We cannot penetrate into the reason of the conjunction.

We only observe the thing itself. We always find that the objects acquire a union in the imagination, from the constant conjunction.

When the impression of one becomes present to us, we immediately form an idea of its usual attendant. Consequently, we may establish this as one part of the definition of an opinion or belief, that it is an idea related to or associated with a present impression.

Causation is a philosophical relation implying contiguity, succession, and constant conjunction.

Yet we are able to reason on it or draw any inference from it only as it:

  • is a natural relation, and
  • unites our ideas.


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