Angelika asked:

I’m trying to understand the differences and similarities to Kant and Hume’s theory about cause and effect.

Can you explain the the basics in which they are similar and different from each other?

Answer by Martin Jenkins

David Hume

In his Enquiry Concerning Human Understanding (1748) Hume argues that all human knowledge is derived from ideas, the relation between ideas and impressions, matters of fact. This knowledge, when reflected upon, displays regularity, displays coherence, it is not chaotic and arbitrary although Hume finds the opposite or contrary of this regularity perfectly possible. So he deduces experience displays resemblance, contiguity and causality.

With resemblance, there is a picture and what the picture represents or resembles; with contiguity there is the inherence of one thing in another as when we think of a room, we cannot but think it as being in a house, and with causality, one thing is said to cause an effect as when an injury causes pain. Without the one thing, the consequent cannot follow or where the impression of one thing leads us to the impression of another.

Causality is for Hume, the basis for many of our inferences and deductions about the world. We infer that the daylight is the effect caused by the sun rising every morning and that this will continue; that the intentions (cause) of a friend to travel to France are evidenced by a letter received from him (effect); that bread has a positive effect on me caused by the nourishing powers contained therein. In other words, our experienced world of matters of fact is assumed to continue as it has in the past; so much so that we make causal inferences and predictions on their basis.

It is perfectly and logically possible that such continuity may cease. That falling snow may taste of salt, that bread may cease to be nourishing, that the sun may not rise tomorrow. Yet as someone once remarked: ‘Would you want to put money on it?’

Yet thinking about the issue raises problems: what demonstrative grounds can we have that prove, that guarantee the future will be the same as the present and past? Only upon such grounds can we genuinely infer from the present into the future and more importantly, rest secure in all our causal reasoning.

The answer for Hume, was that the impressions of the constant conjunction of things such as bread and nourishment, the sun and daylight, snow and cold, candle flame and heat give rise to the custom or habit of associating the qualities. The cause of an effect is not any ‘power’ or ‘necessary connection’; it is again, the constant conjunction of events giving rise to the habit, expectation associating the two events.

"Our idea of necessity and causation arises entirely from the uniformity observable in nature, where similar objects are constantly conjoined together and the mind is determined by custom, to infer the one from the appearance of the other. These two instances form the whole of that necessity which we ascribe to matter. Beyond the constant conjunction of similar objects and the consequent inference from one to the other, we have no notion of any necessity or connexion." (VII. Liberty and Necessity)

There is just the constant conjunction of things and the experience of this displayed uniformity of nature. People abstract from this and project it into the future and why shouldn’t they? There is just the uniformity of nature and where there are experienced anomalies, they do not threaten the uniformity of nature. There is no necessary connection or cause and effect, this being a predisposition of humans to posit a necessity in phenomena. This is superfluous, there is just the uniformity of nature and the constant conjunction of events. Nothing more is required.

Immanuel Kant

Kant remarked that Hume had woken him up from his dogmatic slumber. Despite Hume concluding that epistemologically, all we can observe is the constant conjunction of events and apparently finding this unproblematic, Kant did not.

Besides having interests in philosophy, Kant had interests in the natural sciences. He was perturbed by the possibility of Newtonian natural science being undermined if there were no necessary causal connection with phenomena. Similarly, Hume had not solved the problem of future experience being radically different to present experience which remained possible if, there were no further guarantee than that of experience alone. As such, human knowledge would be contingent, lacking certainty. In his Critique of Pure Reason Immanuel Kant outlines his Critical Idealism which was proffered as the true foundation of Human Knowledge.

Essentially, there are ‘transcendental categories’ which are synthesised with empirical intuitions, an act which both creates and limits human knowledge by synthetic a priori judgements. Relying on impressions alone — as Hume had argued — cannot provide apodeictic certainty for human knowledge claims. (Apodeictic: knowledge claims which are incontestably true because clearly, logically demonstrated.) Knowledge claims based on experience alone would be contingent, unreliable and wholly subjective. With reference to cause and effect, Hume concludes that we never observe the power of cause and effect. From an empirical perspective, this is correct — all that can be observed is one event then another. Hume’s solution of constant conjunction, does not provide any grounds for causality, it more or less dismisses it — laying the grounds for scepticism. Nor can it provide any empirical evidence for the succession of time. On the other hand, according to Kant, transcendental categories of relation (relation: substance, causality, interaction) actualised under the forms of time and space account for the matter of causality (the observed act itself) and the form of causality (what makes the act possible).

The category of substance provides the foundation upon which, changes, modifications occur as mediated by time. For something has to underpin the changes that occur, something which changes without ceasing to exist. An object may be red at one moment and brown at another but something has to be subject to the change. Kant writes in the Critique:

"In other words, the objective relation of the successive phenomena remains quite undetermined by means of mere perception. Now in order that this relation may be recognized as determined, the relation between the two states must be so cogitated that it is thereby determined as necessary, which of them must be placed before and which after, and not conversely. But the conception which carries with it a necessity of synthetical unity, can be none other than a pure conception of the understanding which does not lie in mere perception; and in this case it is the conception of ‘the relation of cause and effect,’ the former of which determines the latter in time, as its necessary consequence, and not as something which might possibly antecede (or which might in some cases not be perceived to follow). It follows that it is only because we subject the sequence of phenomena, and consequently all change, to the law of causality, that experience itself, that is, empirical cognition of phenomena, becomes possible; and consequently, that phenomena themselves, as objects of experience, are possible only by virtue of this law." (B. Second Analogy. Analogies of Experience)

Due to the transcendental intuition of time, we perceive phenomena as occurring successively. Kant employs the example of pouring water into a jar which causes it to overflow. Thus the actions of cause and effect, determined in time are observable. Whilst determined in time, surely, time itself is not the determination of causality?

The example of the water and jar causality leads to the conception of action; action to the conception of force and this, to the conception of substance. Action involves force(s). Forces can alter the state(s) of a substance in varying degrees of intensity; this is a process in matter determined by the form of time.

"Now every change has a cause which evidences its causality in the whole time during which the change takes place. The cause therefore, does not produce the change all at once, in one moment but, in a time so that, as the time gradually increases from the commencing instant A to its completion B, in like manner also, the quantity of the reality B — A is generated through the lesser degrees which are contained between the first and the last. All change is therefore possible only through a continuous action of causality which, insofar as it is uniform, we call momentum. The change does not consist of these momenta but is generated or produced by them as their effect." (ibid)

So causality is understood through the synthesis of the forms of the transcendental categories in time and the forces, changes in matter. This is not acquired through empirical observation alone (as the empiricists maintain) thereby having no guarantee of its necessity and universality (i.e. it might not happen again) but through the synthesis of the categories and intuitions thereby guaranteeing necessity and universality.

I don’t think Hume is similar to Kant in any way. Hume, strictly adhering to his position that knowledge is derived from experience or the relation between ideas, denies the existence of cause concluding that there is only constant conjunction upon which we customarily accept the uniformity of the world. For Kant, this is almost tautologous: experience will continue as it has because experience teaches so. There is no external guarantee beyond experience which is contingent, unreliable and subjective. Apodeictic certainty is required and this is contained in the structuring of our experience by the transcendental categories — which includes causality.

Hope this is useful Angelika.