David Hume and Immanuel Kant on Causation

David Hume and Immanuel Kant are not merely two of the most important figures in the history of philosophy, but two figures whose work is deeply interconnected. Indeed, David Hume’s place in the history of philosophy has often – erroneously – relegated him to the status of ‘Kant’s forebear’, rather than an original and convincing philosopher in his own right.

Regardless, understanding Kant means understanding Hume, and vice versa. This article examines the relationship between Hume and Kant’s theory of causality and its relationship to their philosophies tout court. It begins with a discussion of Hume’s influence on Kant, before moving on to address the relationship between the philosophical justification of causality and the various grounds on which we can make sense of reality. It concludes with a discussion of Kant’s solution to Hume’s skepticism about our ability to understand the world.

The history of philosophy is the history of reaction. This is a cliché, but worth repeating anyway. In no other humanistic discipline is there such a strong tradition of responsiveness. The self-conscious creation of genealogies, inheritances, and relationships of response is inseparable from philosophical activity. It would be difficult to argue that any philosophically reactive relationship deserves more of our attention than the one between David Hume and Immanuel Kant, specifically the relationship between their respective treatments of the topic of causation.

There are three reasons why this relationship is worthy of attention.  First, they are two of the most important modern philosophers, both in terms of how broad and distinctive their philosophical work is and in terms of how influential their work has proven to be. Second, the relationship between David Hume’s work and that of Immanuel Kant is direct and indisputable. As we shall see, Kant was exceptionally clear about the debt he owed to David Hume, and the wide-ranging effect Hume had on Kant’s philosophical development. Lastly, although the effect Hume had on Kant is not in dispute, the exact terms of that influence are extremely hard to pin down. Philosophers disagree not only in what Kant learned from Hume but in what Kant and Hume taken separately had to say about causation.

David Hume’s Account of Causation

There isn’t space here to summarize the various interpretations of Hume’s account of causation, so a brief statement of the traditional interpretation will have to do.

David Hume’s theory of causation states that cause and effect relationships are not a product of natural law or universal truth, but are instead based on the necessity that we associate events based on experience. This means that when we observe A happening before B, we assume that A caused B, and this assumption is based on past experience and not on an inherent connection between events.

Hume argued that causation does not exist in the physical world, but rather is simply a construct created in our minds:

“The mind can never possibly find the effect in the supposed cause, by the most accurate scrutiny and examination. For the effect is totally different from the cause, and consequently can never be discovered in it. Motion in the second billiard-ball is a quite distinct event from motion in the first; nor is there anything in the one to suggest the smallest hint of the other. When I see, for instance, a billiard-ball moving in a straight line towards another; even suppose motion in the second ball should by accident be suggested to me, as the result of their contact or impulse; may I not conceive, that a hundred different events might as well follow from the cause? … All these suppositions are consistent and conceivable.”

The effect of Hume’s work on Immanuel Kant was, on his own telling, an exceptionally compelling one. Here is one of the most famous passages in all of Kant’s work: “I freely admit that it was the remembrance of David Hume which, many years ago, first interrupted my dogmatic slumber and gave my investigations in the field of speculative philosophy a completely different direction”.

Elsewhere, Kant is more specific about what it is in Hume’s work that influenced him so:  “no event has occurred that could have been more decisive for the fate of this science than the attack made upon it by David Hume… Hume proceeded primarily from a single but important concept of metaphysics, namely, that of the connection of cause and effect”.

It is important to be clear from the outset that Kant does not appear to accept Hume’s account of causation. In fact, Hume influences Kant by laying down a philosophical challenge: that of removing “the Humean doubt from the ground up.”

A Solution to the Humean Problem

Kant set his sights on a way of resolving the Humean problem which would preserve what he believed to be “pure concepts of the understanding” and the validity of the general laws of nature. To do so, he believed that these concepts should be taken to apply only to our experience, and he sought to investigate the ways in which these concepts ground the possibility of experience. Kant’s trick was the following: these concepts are not – as Hume believed – derived from experience, but “experience is derived from them, a completely reversed kind of connection which never occurred to Hume.”

He takes Hume’s claim that appearances cannot themselves provide a ground for any necessity for the succession of appearances seriously. “Appearances certainly provide cases from which a rule is possible in accordance with which something usually happens, but never that the succession is necessary; therefore, a dignity pertains to the synthesis of cause and effect that cannot be empirically expressed at all, namely, that the effect does not merely follow upon the cause but is posited through it and follows from it.”

Kant is about removing contingency and partiality from the judgments of experience – truths of experience do not just have the warrant of experience, but something a priori.

“I understand very well how a consequent may be posited through a ground in accordance with the rule of identity, because it is found to be contained in [the ground] by the analysis of concepts. … I call the first kind of ground a logical ground, because its relation to the consequent can be logically comprehended in accordance with the rule of identity…I pose my question in this simple form: how can I understand the circumstance that, because something is, something else is to be?”

Hume’s challenge to reason is, in effect, the challenge of how to give an account of necessary causal connection. The Kantian solution to this problem is the construction of the synthetic a priori, a concept that is neither that which we know by reason, nor by the analysis of what is contained within predicates. The synthetic a priori is the basis on which we are able to come to know something new from the analysis of pure experience, and the only way we can reach truths about the world that are necessary but not based on logical considerations.

The Necessity of Causation: Immanuel Kant’s Resolution

Kant’s view of causation was simply that “the succession is necessary; … the effect does not merely follow upon the cause but is posited through it and follows from it…the very concept of cause so obviously contains the concept of a necessity of the connection with an effect and a strict universality of the rule, that the concept [of cause] would be entirely lost if one pretended to derive it, as Hume did, from a frequent association of that which happens with that which precedes, and [from] a thereby arising custom (thus a merely subjective necessity) of connecting representations”.

Contemporary scholars Graciela De Pierris and Michael Friedman explain what Kant was responding to in the following way: “Hume maintains that the idea of the effect is never contained in the idea of the cause (in Kant’s terminology, the relation is not analytic), and thus, according to Hume, it is never knowable a priori. We therefore need experience in the Humean sense in order to make any causal claims”. Kant, in contrast, attempts to accept and incorporate the skeptical element of Humean thought without any negative implications for our ability to make sense of the world, meaning – for Kant – to ascribe objectivity to our concept of it.