The immorality of lying promises does not consist in a simple self-contradiction of the maxim itself.

Kant’s example of a perfect duty to others concerns a promise you might consider making but have no intention of keeping in order to get needed money. Naturally, being rational requires not contradicting oneself, but there is no self-contradiction in the maxim “I will make lying promises when it achieves something I want.” An immoral action clearly does not involve a self-contradiction in this sense (as would the maxim of finding a married bachelor). Kant’s position is that it is irrational to p