Critique of Pure Reason: Encyclopedia II - Critique of Pure Reason - Kant's rejection of Hume's empiricism

Critique of Pure Reason - Kant's rejection of Hume's empiricism

Hume's conclusions, Kant realized, rested on the premise that knowledge is empirical at its root. The problem that Hume identified was that basic principles like cause and effect cannot be empirically derived. Kant's goal, then, was to find some way to derive cause and effect without relying on empirical knowledge. Kant rejects analytical methods for this, arguing that analytic reasoning can't tell you anything that isn't already self-evident. Instead, Kant argued that we would need to use synthetic reasoning. But this posed a new problem—how can one have synthetic knowledge that is not based on empirical observation—that is, how can we have synthetic a priori truths.

Kant concluded that there are synthetic a priori truths. He reasoned that geometry and Newtonian physics are synthetic a priori knowledges and are fundamentally true and wanted to establish how this could be possible. This also led him to inquire whether it could be possible to ground synthetic a priori knowledge for a study of metaphysics, because most of the principles of metaphysics from Plato through Kant's immediate predecessors made assertions about the world or about God or about the soul that were not self-evident but which could not be derived from empirical observation. This led to his most influential contribution to metaphysics: the abandonment of the quest to try to know the world as it is "in itself" independent of our sense experience. He demonstrated this with a thought experiment, showing that we cannot meaningfully conceive of an object that exists outside of time and has no spatial components and isn't structured in according with the categories of the understanding, such as substance and causality. Although we cannot conceive of such an object, Kant argues, there is no way of showing that such an object does not exist. Therefore, Kant says, metaphysics must not try to talk about what exists, but instead about what is experienced and how it is experienced.

This provided Kant with the basis to distinguish between phenomena -- things as they appear to our senses (including the inner sense of time) -- and noumena -- things that are purely objects of thought independently of sense perception, which, by definition, we can never experience -- in Kant's words, "thoughts without content [are] empty, and intuitions without concepts [are] blind". The phenomenon is only the representation of the noumenon that a person receives through their sensibilities and structures in accordance with the categories of the understanding. The noumenon exists as the horizon of our experience of a thing, a horizon that can only be circumscribed with philosophical concepts. Kant's whole metaphysical system, which is based on the operations of cognitive faculties, was meant to describe the world as we experience it—a much more modest task than describing the world as it is beyond our experience of it, which, according to Kant, is what all previous philosophy was mistakenly trying to do.

Kant termed his critical philosophy "transcendental idealism", which for him is intimately linked with empirical realism. That is, our empirical knowledge is real, but it cannot know what transcends the operations of our cognitive faculties. Transcendental idealism describes Kant's method of seeking the conditions of the possibility of our knowledge of the world and recognizes that there are things that transcend the limits of our cognitive faculties. It is because of taking into account the role of our cognitive faculties in structuring the known and knowable world that in the second preface to the "Critique of Pure Reason" Kant compares his critical philosophy to Copernicus' revolution in astronomy. Kant writes: "Hitherto it has been assumed that all our knowledge must conform to objects. But all attempts to extend our knowledge of objects by establishing something in regard to them a priori, by means of concepts, have, on this assumption, ended in failure. We must therefore make trial whether we may not have more success in the tasks of metaphysics, if we suppose that objects must conform to our knowledge" [Bxvi]. Just as Copernicus revolutionized astronomy by changing the point of view and taking the position of the observer into account, Kant's critical philosophy takes into account the position of the knower of the world in general and reveals its impact on the structure of his known world.

Kant's transcendental idealism should be distinguished from idealistic systems such as Berkeley's. While Kant claimed that phenomena depend upon the conditions of sensibility, space and time, and on the synthesizing activity of the mind manifested in the rule-based structuring of perceptions into a world of objects, this thesis is not equivalent to mind-dependence in the sense of Berkeley's idealism. For Berkeley, something is an object only if it can be perceived. For Kant, on the other hand, perception does not provide the criterion for the existence of objects. Rather, the conditions of sensibility (space and time) and the categories of the understanding provide the "epistemic conditions", to borrow a phrase from Henry Allison, required for us to know objects in the phenomenal world.

Adapted from the Wikipedia article "Kant's rejection of Hume's empiricism", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki