The Prolegomena has two related purposes: 1) to defend the integrity of metaphysics as a science, and 2) to forward a new paradigm of knowledge construction. Kant seemed to be concerned more of the first purpose. In the Preface to the book, he said:
“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” (Kant, xvii).
In the first chapter of the book, Kant returned to Hume’s general problem: causality. Kant proposed ‘to make a trial with Hume’s problematic concept, namely the concept of cause” (Kant, 66). Kant argued that it is possible to have a complete solution to the Humean problem as it relates to knowledge construction. Kant said:
The Humean problem rescues the a priori origin of the pure concepts of the understanding and the validity of the general laws of nature as laws of the understanding, in such a way that their use is limited only to experience, because their possibility has its ground merely in the relation of the understanding to experience, however, not in such a way that they are derived from experience, but that experience is derived from them, a completely reversed kind of connection which never occurred to Hume (Kant, 66) – italics mine.
For Kant, the general laws of nature are generally the source of experience. According to him, the constitution of experience is by nature the by product of a priori concepts. Experience is derived from objective reality, as objective reality is defined by experience itself.
In Enquiry, Hume argued that cause and effect are entirely distinct events, where the idea of the former is in no way in the rubric of the latter. Hume said:
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 (Hume in Kant, 59).
Kant’s answer was based on a distinction between ‘logical grounds’ and ‘real grounds.’ According to him, both concepts indicate a relationship between cause and effect. Here, Kant argued that, in the case of a real ground, the relationship between cause and effect is not one of containment, and the judgment that the former follows from the latter is never analytic.
Kant suggested that the relationship between a real ground and its assumed effect can only be derived from experience. He said:
It is impossible ever to comprehend through reason how something could be a cause or have a force; rather these relations must be taken solely from experience. For the rule of our reason extends only to comparison in accordance with identity and contradiction. But, in so far as something is a cause, then, through something, something else is posited, and there is thus no connection in virtue of agreement to be found (Kant, 356).
Kant’s final solution to the Humean problem is expressed in his famous distinction between ‘judgments of perception’ and ‘judgments of experience.’ According to him, empirical judgments are by nature objective – expressed by judgments of experience. However, empirical judgments are only subjectively valid, that is, constrained by the necessity of individualistic validity – an expression of judgments of perception.
Kant successfully synthesized a full understanding of knowledge and causation by suggesting the conversion of mere perceptions into objective experience. This conversion is done by affecting a ‘necessary unification’. Kant concluded, “Therefore, the pure concepts of the understanding are those concepts under which all perceptions must first be subsumed before they can serve as judgements of experience, in which the synthetic unity of perceptions is represented as necessary and universally valid” (Kant, 65).
Kant, Immanuel. Prolegomena to Any Future Metaphysics. Trans. By James W. Ellington (1977) and James Fieser (1997). New York: Macmillan Publishing Company,