In this section, David Hume reveals his scepticism regarding causality and the basis of our conclusions about the world, ultimately questioning the rational foundations of inductive reasoning. I bring forth the key points of Hume’s argument, tracing his analysis of cause and effect, the role of experience in our understanding, and his radical conclusion that our knowledge of the external world rests not on reason but on reoccurring patterns of experience.
Hume’s Fork: Relations of ideas and matters of fact
The first paragraphs introduce an important distinction between what Hume describes as the two objects of human reason: Relations of ideas and matters of fact. This distinction has later been nicknamed Hume’s Fork.
What he means with reasoning through relations of ideas is analytical and abstract reasoning, where the answer is found without needing to call upon experience. This type of reasoning is characterized by intuitive thinking (e.g. all bachelors are unmarried) and demonstrative thinking (e.g. the Pythagorean theorem). Relations of ideas may in more modern terms be translated as analytic a priori1 knowledge.
All the objects of human reason or enquiry may naturally be divided into two kinds, to wit, Relations of Ideas, and Matters of Fact. Of the first kind are the sciences of Geometry, Algebra, and Arithmetic; and in short, every affirmation, which is either intuitively or demonstratively certain. […] Propositions of this kind are discoverable by the mere operation of thought, without dependence on what is any where existent in the universe (Hume 2007, p. 18).
Matters of fact on the other hand are characterized by inferential reasoning — also called probable reasoning by John Locke, or moral reasoning by Hume — which is always dependent upon experience in order to be justified. Examples of this may be that “water is wet”. There is no way of knowing that water is wet without consulting experience first. Hence, this may instead be translated into synthetic a posteriori knowledge in modern terms.
His division may be more easily encapsulated as:
- There are statements about ideas. These are analytic, necessary and knowable before experience (i.e. a priori).
- There are also statements about the world. These are synthetic, contingent2 and only knowable after calling upon experience for justification (i.e. a posteriori).
However, Hume points out that it is very misleading to put these types of knowledge beside each other. This, because of how different knowing a matter of fact is compared to knowing that 2 + 2 = 4.
Matters of fact, which are the second objects of human reason, are not ascertained in the same manner; nor is our evidence of their truth, however great, of a like nature with the foregoing. The contrary of every matter of fact is still possible; because it can never imply a contradiction, and is conceived by the mind with the same facility and distinctness, as if ever so conformable to reality. That the sun will not rise to-morrow is no less intelligible a proposition, and implies no more contradiction, than the affirmation, that it will rise (Hume 2007, p. 18).
When reasoning about relations of ideas it is clear for Hume that reason alone guides to the truth of the statements, he is not as convinced that it is also so concerning matters of facts. And so, Hume launches an enquiry into what matters of fact really are based upon.
The nature of all our reasonings concerning matter of fact
It is quickly ascertained that “All reasonings concerning matter of fact seem to be founded on the relation of Cause and Effect” (Hume 2007, p. 19). Seemingly intuitive, he decides not to spend time defending why this is so, and instead quickly moves forward by exposing a queer artifact of this thinking pattern.
The very idea of causality presupposes that there is a connection between a present fact (such as kicking a football) and what is inferred from that fact (the football moving). By what rational basis may we justify that my kicking is the very thing which leads to the effect of moving? This idea of “necessary connection” as he calls it, becomes the next target of inquiry, a connection which most take for granted, but Hume does not.
The foundation of reasonings and conclusions concerning cause and effect
Are we able to understand cause and effect as soon as we are born? Seems unlikely, since we can’t orient ourselves, or produce anything but a cry for help for that matter. So, it seems that we learn this way of thinking. And how do we learn it? How does any human learn anything? By observation, by experience.
This is essentially Hume’s argument as to what the principle of cause and effect relies upon for justification.
I shall venture to affirm, as a general proposition, which admits of no exception, that the knowledge of this relation is not, in any instance, attained by reasonings à priori; but arises entirely from experience, when we find, that any particular objects are constantly conjoined with each other (Hume 2007, p. 19).
One learns that if enough force is applied on an object, it tends to move. There is no way of deducing this before having gathered experience.
Our understanding of cause and effect, such as the notion that applying sufficient force to an object will cause it to move, is derived entirely from experience rather than logical reasoning. Even if one were to thoroughly examine an apple’s sensible qualities, such as its colour, weight, and consistency, one could not logically deduce that it is movable without first experiencing its motion3.
The foundation of all conclusions from experience
After having achieved a satisfactory answer as for the questions of what the nature of all our reasonings concerning matter of fact is (the principle of cause and effect) and what the foundation of all our reasonings and conclusions concerning that relation is (experience), Hume reaches the final stage of the investigation. Here, he inquires about the basis for our conclusions derived from experience itself.
His main concern in this final stage of the investigation is to highlight the impossibility of rationally justifying that the future will resemble the past.
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. 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 (Hume 2007, p. 25).
This assumption cannot be justified through reasoning, it would be circular to attempt to prove through probable arguments that the future will resemble the past, since all probable arguments are themselves based on that very supposition.
He suggests that the principle of cause and effect may be observed when looking at how infants and animals improve by experience. They learn to expect similar effects from apparently similar causes, strengthening the argument that this principle is not grounded in sophisticated reasoning but is rather a fundamental aspect of how we learn from experience.
Hence, Hume’s final stance is that our belief that an object is movable when sufficient force is applied is not a logical necessity, but an inference based on the consistent conjunction of similar causes and effects in our experience. The apparent connection between the sensible qualities of an object and its secret powers, such as mobility, is not something that can be deduced a priori but is rather discovered through repeated observation. The conclusion is revolutionary, our reasoning concerning matters of fact is not rationally justifiable.
Final thoughts
The turn of events in this section leaves the reader in a rational vacuum. Luckily, Hume is not nihilistic, just a very good investigator. Even if he has discovered how questionable our method of inductive reasoning is, how void of rational basis it truly is, he still sees a way of moving forward. The alternate and more consistent explanation relies on his ideas of custom and habit, concepts which will be explored and discussed in the next section, section V.
Hume, D. (2007) An enquiry concerning human understanding. Oxford; New York: Oxford University Press (Oxford world’s classics).
- Note that for Hume a priori knowledge can only be analytic, not synthetic like Immanuel Kant proposed.
- In philosophy and logic, contingency refers to the status of propositions or events that are neither necessary nor impossible. A contingent statement or event is one that could be true or could happen, but it is not guaranteed to be true or to happen in every possible circumstance. It stands in contrast to necessary statements, which must be true, and impossible statements, which cannot be true.
- Hume uses the term “secret powers” to refer to the inherent capabilities or forces within objects that produce effects, which are not directly observable through their sensible qualities. It includes all the hidden causal forces within objects that produce effects, which we come to understand through experience rather than direct observation or logical deduction.