The core concept of Kant's moral philosophy is "Pure practical reason" and it has become an important part of western moral philosophy. The thought of practical reason can best reflect Kant's criticism and reflection on the enlightenment. However, in the early development of Kant's ethics,he did not directly to establish pure practical reason the foundation of his moral philosophy. Under the profound influence of emotivism ethics, he thought of the "emotion" factor as the driving force of morality, and intended to reconcile emotivism and rationalism. In the "pre-critical period", he gradually clarified the basic position of pure practical reason.
So what is the fundamental matter of pure practical reason? Kant held that "pure reason itself can be practical", that is, it explains the practical application of pure reason. To discuss this issue, we should first explain the cause of "why the moral law from pure reason can be practical", that is, "in what way does the moral law become motive". But because this kind of cause is congenital knowledge and beyond the cognitive limits of human reason. Therefore, Kant turned to the effect of moral motivation in the mind -- "respect" as a moral motivation, which focused on the relevant chapters of the Foundation of Moral Metaphysics and the Critique of Practical Reason. So it can be considered that the explanation of the motivation of pure practical reason touches on the core issue of Kant's moral philosophy.
However, on the one hand, there are many ambiguities in Kant's discourse on "respect"; on the other hand, in the context of the revival of the contemporary "virtue ethics", a large number of "Internalists" represented by Williams have appeared, and they made profound criticism on the "normative moral motivation" including Kant's ethics. Although the following group of Kantians refuted with the analysis of moral psychology, they deviated from the original intention of Kant to some extent, so Kant's motivation theory of pure practical reason was in a situation of internal and external troubles. In this context, this paper retains Kant's transcendental position to the greatest extent and combines with Kant's epistemological content to try to respond to the criticism of contemporary empiricists