David Hume’s problem of induction makes for an interesting case study in which to see the division between intellectualism and conceptualism play out. Below I state what Hume takes the problem to be. Elsewhere, I discuss Popper’s conceptualist treatment of Hume’s problem.
The problem stated
In An Enquiry Concerning Human Understanding, Hume examines the sources of human knowledge, which he describes as reasoning about either the relation of ideas or about matters of fact. But he quickly discovers a kind of inference that men make in all areas of life which he can ground in neither of these two types of reasoning. He gives several examples of this sort of inference, but an oft repeated one concerns inferring from past instances of being nourished by eating bread to the same effect in the future when consuming bread.
The bread, which I formerly ate, nourished me; that is, a body of such sensible qualities was, at that time, endowed with such secret powers: But does it follow, that other bread must also nourish me at another time, and that like sensible qualities must always be attended with like secret powers? (1)
Hume then states the structure of the inference in more precise terms:
“These two propositions are far from being the same,
- I have found that such an object has always been attended with such an effect and,
- I foresee, that other objects, which are, in appearance, similar, will be attended with similar effects.” (2)
Hume’s empiricism only allows for two sources of, or kinds of objects for, human knowledge, namely relations of ideas and matters of fact, so he examines each one in turn to see if an inductive inference of this sort can be founded upon either.
Of matters of fact
When it is asked, What is the nature of all our reasonings concerning matters of fact? the proper answer seems to be, that they are founded on the relations of cause and effect. When again it is asked, What is the foundation of all our reasonings and conclusions concerning that relation? it may be replied in one word, Experience. (3)
Uncontroversially, then, matters of fact are known by humans through experience. Additionally, Hume associates knowledge of cause and effect through experience with the recognition of similarity.
In reality, all arguments from experience are founded on the similarity which we discover among natural objects, and by which we are induced to expect effects similar to those which we have found to follow from such objects… From causes which appear similar we expect similar effects. This is the sum of all our experimental conclusions. (4)
Cause and effect appears to be founded on experience through the principle of similarity. However, when experience is examined, it is discovered that nothing in the nature of experience, with the information it gathers from particular objects, each of which are found in discrete places and times, justifies the inference from past experiences to future experiences.
As to past experience, it can be allowed to give direct and certain information of those precise objects only, and that precise period of time, which fell under its cognizance: But why this experience should be extended to future times, and to other objects, which for aught we know, may be only in appearance similar, this is the main question on which I would insist. (5)
Of relations of ideas
Since these inductive inferences cannot be grounded in experience, Hume pleads to be told by what sort of reasoning we are justified in making the inference.
When a man says, I have found, in all past instances, such sensible qualities conjoined with such secret powers: And when he says, Similar sensible qualities will always be conjoined with similar secret powers; he is not guilty of a tautology, nor are these propositions in any respect the same. You say that the one proposition is an inference from the other. But you must confess that the inference is not intuitive; neither is it demonstrative. (6)
And again:
I shall allow, if you please, that the one proposition may justly be inferred from the other: I know, in fact, that it always is inferred. But if you insist that the inference is made by a chain of reasoning, I desire you to produce that reasoning. (7)
Much like his narrow notion of experience, Hume has a narrow notion of what constitutes reasoning regarding the relations of ideas.
Of [the relations of ideas] 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 hypotenuse 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. (8)
This is a typical laundry list of a priori ways of thinking.
Since the relation of cause and effect is neither intuitive nor demonstrative, then it cannot be counted among the kinds of human reasoning for Hume.
Of habit
From the failure to ground cause and effect relations in either reasoning about relations of ideas or matters of fact, Hume concludes that cause and effect is not the result of any rational, cognitive process, but is grounded in habit.
The generality of mankind never find any difficulty in accounting for the more common and familiar operations of nature – such as they descent of heavy bodies, the growth of plants, the generation of animals, or the nourishment of bodies by food…
They acquire, by long habit, such a turn of the mind, that, upon the appearance of the cause, they immediately expect with assurance its usual attendant, and hardly conceive it possible that any other event could result from it…
But philosophers, who carry their scrutiny a little farther, immediately perceive that, even in the most familiar events, the energy of the cause is as unintelligible as in the most unusual, and that we only learn by experience the frequent conjunction of objects, without being ever able to comprehend anything like connexion between them. (9)
This reads as though men become accustomed to the constant correlation of “one thing, then another” in nature, but are never rationally justified in calling this causation. And philosophers appear to do not better in Hume’s estimation.
Notes:
- David Hume, An Enquiry Concerning Human Understanding, p. 35
- ibid., p. 35
- ibid., p. 34
- ibid., p. 37
- ibid., p. 35
- ibid., p. 38
- ibid., p. 35
- ibid., p. 28
- ibid., pp. 64 – 65
Dissertating Outloud 