b) Kantian adoption of the principle of the distinction between practical and theoretical spheres

This concept, situating morality within the practical rather than the theoretical sphere, appears to have gained broad acceptance, despite competition from the Stoic tripartition, which divides knowledge into ethics, logic, and physics, even extending to Kant, who seems to have embraced its essence.
Kant presents his moral philosophy in the Critique of Practical Reason. However, his reasons differ from those of Aristotle; he does not place morality in the practical sphere based on principles of movement or degrees of certainty regarding its object, but rather on a distinction between what falls under our freedom and what does not.

Kant distinguished between the theoretical and practical spheres as early as 1770: Something is considered theoretically when we attend only to what belongs to the thing; practically, when we view what by liberty should be in it ¹.
Kant most explicitly defines this in the Critique of Practical Reason: [what] is practical for us, i.e., to be realized by our will ².
Thus, practical knowledge pertains to that which involves imperatives, whereas Theoretical cognitions are those which express not what ought to be, but what is; and therefore have as their object not an action but a fact ³.

Therefore, Kant defines the practical field based on freedom, will, and imperatives, rather than the Aristotelian principles we discussed earlier. Nonetheless, the central idea remains consistent: morality belongs to the practical field.

c) The consequence of attributing morality to the practical sphere

The notion that morality belongs to the practical sphere has, in my view, led thinkers to ascribe to it certain characteristics associated with praxis.
Firstly, praxis is fundamentally action, distinct from what might be mistaken for action—namely, production (poiésis). This distinction has led to understanding morality as the study of a specific facet of action. Since this action is carried out by humans, morality came to be viewed as the study of a particular quality of human action. From this, it was concluded that studying morality involves examining both action and its human dimension. Thus, the object of morality is human action.
R. Misrahi, for example, offers this definition of morality: Morality, in traditional thought, designates the part of philosophy devoted to the search for the best principles of conduct ⁴. He assigns a similar meaning to ethics, describing it as the philosophical reflection that seeks to define principles for the conduct of life ⁵. However, for the purposes of this research, ethics is more a meditation on happiness than on duty.

The idea that morality concerns action and human beings seems broadly accepted. It is true that Kant argues morality concerns all rational beings, not only humans; yet this includes humans and thus does not contradict the consensus we are outlining. On the other hand, some thinkers suggest that the object of morality lies more in human character—in other words, in something related more to 'being' than 'doing'. However, this perspective only holds because we attribute to 'being' the power to influence action.
Thus, human action remains, fundamentally, the object of morality. (The same reasoning applies if we believe morality lies in intention rather than action; morality is still considered as such because it ultimately leads to action.)

Our objective here is to determine what conception of value may have indirectly led to this view of morality. Since, as we have attempted to demonstrate, the conception of value has developed through morality—with morality absorbing axiology—this view of morality as part of the practical, rather than theoretical, sphere must have influenced the conception of value.
In my view, the primary consequence is a tendency to consider axiology as a practical science, akin to ethics, politics, and economics, rather than as a theoretical science like mathematics or physics. In the contemporary framework of knowledge, disciplines studying human action are generally classified as 'human sciences' in contrast to the 'exact sciences'. As a result, the vague conception of axiology that typically comes to mind situates it within the human sciences.

This brings us to two related questions: 'Is axiology a practical or theoretical science?' and 'Is axiology a human science?'

1. The Form and Principles of the Sensible and Intelligible World, §9, note ; AK I, 396
2. Critique of Practical Reason, Book II, ch. II, I
3. Introduction to Logic, Introduction, Appendix, AK IX, 86-87
4. Qu’est-ce que l’éthique ? p. 254
5. Ibid., p. 241