He explains radical evil as corruption that entirely takes over a human being and leads to desires acting against the universal moral law.
The outcome of one's natural tendency, or innate propensity, towards evil are actions or "deeds" that subordinate the moral law.
[1][2] By many authors, Kant's concept of radical evil is seen as a paradox and inconsistent through his development of moral theories.
Now although this does not always give rise to wrong actions and a propensity thereto, that is, to vice, yet the habit of regarding the absence of vice as a conformity of the mind to the law of duty (as virtue) must itself be designated a radical perversity of the human heart (since in this case the spring in the maxims is not regarded at all, but only the obedience to the letter of the law).
"[7] Categorical imperatives (Cl) is the foundation of morality in which Kant uses to create the phrase radical evil.
Propensity therefore is distinguished as a tendency, or inclination, in one's behavior to act accordingly or opposed to the moral law.
Kant changes his supporting arguments and claims in his work that some philosophers found as "scandalous", "inconsistent", and "indecisive".