source

Kant initiated his own “Copernican revolution” when he challenged philosophers with a new theory of knowledge. The human mind contains categories that structure all sense perceptions and these categories are necessary for understanding the phenomenal world of experience. Rather than our knowledge adjusting to sensory input, the sensory input adjusts to our knowledge.

Knowledge of the phenomenal world consists of a combination of content and form. Content is
the “stuff” of sense perception, it is what is given to the mind. Without content or sense
experience there would be no genuine knowledge. Yet, content alone is not sufficient for
human knowledge to obtain. It must have a place to go or a space to fill in the human mind.
Forms are the categories into which we fit the content of all sense perception. Without sense
perception, the categories would be empty space.

Sense perceptions, then, are received through these categories that subsist in the mind. That
is, there is no objective thing-in-itself (Ding an sich) that can be perceived. Since all experience is filtered first through the a priori operations of the mind, what turns out to be known is the object as it appears. Consequently, a wall is erected between two continua: the noumena (the world-in-itself) and the phenomena (the world as it appears). It is as if life is seen through the tube of a black and white television. The viewing is a mere “representation” of what the (colorful) world-in-itself looks like. Sensory percepts are always modified by a priori concepts, capable of seeing only the “black and white” world.

What makes human knowledge possible, according to Kant, are the a priori categories
uncovered by a process of “transcendental deduction.” Though his epistemological system is
“trancendentally ideal,” because there is no direct knowledge of the noumenal world-in-itself,
we do have the phenomenal world of sense perceptions whereby we can know something with
universality and necessity, qua phenomena. Kant maintained that sense data is organized by
the mind’s categories, some of which include unity, plurality, causality, time, and space. Theseare a priori conditions under which we can have knowledge of the external phenomenal world.

However, they do not serve to offer any help in knowing the noumenal world, or things-in themselves.

This is the transcendental world that can only be postulated by reason.
The theological implication is that reliable, objective knowledge about God cannot be obtained,since God is restricted to the noumenal realm and nothing of this realm can be directlyapprehended. God cannot be experienced, only postulated. Human knowledge is limited to the phenomenal world–the world as it appears.