One of the most basic disputes concerning the interpretation of Kant's ethics concerns the relationship between the different formulations of the categorical imperative presented in the Groundwork. One of the problems, mentioned sometime ago by Paton, concerns the question of how many such formulations there are with Paton favouring five but most commentators now content to think there are three. A rather more substantive concern has been with the practical implications of the distinct formulas with a wide variety of thinkers wishing to suggest that there are different implications relative to which version of the categorical imperative one adopts.
In particular there is a general felt need to choose between the formula of universal law and the formula of humanity. The partisans of the formula of universal law are, for various reasons, on the defensive though the major gain of this formula, relative to others, concerns its implicit appeal to a neutral standard separate from the "matter" of moral commitments. This is bought, allege the critics of this formula, at a cost, namely, the vacuous nature of what the formula is taken to state. This argument can trace its ancestry to Hegel and consists in a claimed "empty formalism" of the formula of universal law. Confronted with this type of attack on Kant's ethics it has been a generally adopted defence to argue that the formula of universal law is not the central Kantian principle.
So, on these grounds, the appeal has often been made to the formula of humanity by preference to the formula of universal law. There are advantages to stressing this formula, not least the intuitive appeal of the contrast it involves between ends-in-themselves and ends that are only relative. This contrast is connected to a conception of humanity that effectively equates humanity with rationality. Since this line of thought hence moves from humanity to rationality to a stress on "objective" or non-relative ends it has the makings of an incipient theory of practical reason. However, there are compensating problems with this stress, though these have not been at the forefront of much discussion. To begin with, the equations involved in the formula are ones that are far from obvious and call out for detailed defence. Secondly, the formula of humanity is itself described in such a way that it is evidently meant to be understood as universal in scope. So if there are thought to be problems with universality itself then these problems would apply also to the humanity formula. Thirdly, the resort to it as a defence against the "empty formalism" objection is one that threatens to turn Kant's ethics into one that asserts a need for an end or even a substantive conception of the good. In other words, the conflict, should there really be one, between these two formulas of the categorical imperative, is one that can re-stage within the terrain of Kantian ethics, the division between "teleological" and "deontological" views of the general area of ethics. In subsequent postings I intend to trace this division and debate it further in order to see whether it is possible to get a view of both Kant's ethics and the area of ethics generally that can move past this divide.