b) Kantian Adoption of the Principle of the Distinction Between Practical and Theoretical Spheres

This conception, which situates morality within the practical rather than the theoretical sphere, appears to have gained broad acceptance—notwithstanding competition from the Stoic tripartition, which divides knowledge into ethics, logic, and physics—and extends even to Kant, who seems to have embraced its essential thrust.
Kant presents his moral philosophy in the Critique of Practical Reason. His reasons, however, differ from those of Aristotle: he does not place morality in the practical sphere on the basis of 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 drew this distinction 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.
He defines it most explicitly in the Critique of Practical Reason: [what] is practical for us, i.e., to be realized by our will ².
Practical knowledge thus 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.

Kant therefore defines the practical field in terms of freedom, will, and imperatives, rather than the Aristotelian principles discussed earlier. The central idea nonetheless 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.
In the first place, praxis is fundamentally action, distinct from what might be mistaken for it—namely, production (poiésis). This distinction has led to an understanding of morality as the study of a specific facet of action. Since this action is carried out by human beings, 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. The object of morality is thus human action.
R. Misrahi, for example, offers the following 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 comparable meaning to ethics, describing it as the philosophical reflection that seeks to define principles for the conduct of life ⁵. For the purposes of the present inquiry, however, ethics is better understood as a meditation on happiness than on duty.

The idea that morality concerns action and human beings seems broadly accepted. Kant, it is true, argues that morality concerns all rational beings and not only humans; yet this includes humans and therefore does not contradict the consensus we are outlining. Some thinkers, on the other hand, suggest that the object of morality lies more in human character—in something pertaining more to 'being' than to 'doing'. This perspective, however, is only tenable because we attribute to 'being' the power to influence action.
Human action thus remains, fundamentally, the object of morality. (The same reasoning applies if we hold that morality lies in intention rather than action; morality is still regarded as such because intention ultimately issues in action.)

Our aim here is to determine what conception of value may have indirectly given rise 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 belonging to the practical rather than the theoretical sphere must have shaped the conception of value.
The primary consequence, in my view, is a tendency to regard axiology as a practical science, akin to ethics, politics, and economics, rather than as a theoretical science like mathematics or physics. Within the contemporary framework of knowledge, disciplines that study 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 places 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, Part 1, Book II, ch. II, I
3. Introduction to Logic, Introduction, Appendix, AK IX, 86-87
4. Qu’est-ce que l’éthique ? Armand Colin, Paris, 1997, Glossaire analytique, « Morale », p. 254
5. Ibid., Glossaire analytique, « Ethique », p. 241