In Kant’s famous work, “The critique of pure reason”, he shows that our ability to understand our world is on the basis of sense perception. Anything beyond sense perception is not knowable in and of itself (other than time and space). Thus the only apriori is our rational thought processes. The way we think about our environment is “intrinsic”. He does not exclude the possibility of “something beyond” but for the sake of his critique, says we can’t know it on our own. A reformed theologian would add that this is the “barrier that our faithful God breaks through, in His sovereignty” with His message of reconciliation for us.
Enter the second of Kant’s famous works “The critique of practical reason” or his approach to ethics. In this work he emphasizes that ethical action is best based on non-self interested duty, coming forth from a “good will” and informed by “maxims (rules)” that are derived not from empiric situations but from an apriori principle of behavior that all rational beings hold in common. He calls this apriori principle “the categorical imperative” and defines it as follows:
“Act in such a way that you always treat humanity whether in your own person or in the person of any other, never simply as a means, but always at the same time as an end”. He also puts it another way “Act in such a way that if the action was repeated over and over, it could be accepted as the basis for a universal moral law”
This definition illustrates very important principles in his approach to ethics: 1. Ethical action is never based on situational events only but always on an underlying principle (ethics is normative). 2.Ethical action is at its best when it is coming from duty (deontology) as opposed to self interest only. 3. The Categorical Imperative ethical principle has its basis in truth which Kant anchors in the “objective principle or the end in itself” namely our rational nature. This rational nature is how we conceive our existence and is consensually valid (ie it is a principle that crosses cultural/religious /personal boundaries). The basis by which we conceive of ourselves as rationally free beings is a universal commonality. This conception can then by applied to ethical decision making. A conception which at its core seeks truth to inform itself.
In his work, Religion Within the Bounds of Pure Reason, Kant then describes how religious principles can be used to inform the deontological reasoning process.