In Chapter 11 of his commentary on the Groundwork Allison looks at two questions concerning the interpretation of the third section of the work. On the one hand, he assesses the way freedom is discussed here and on the other looks at the nature of the apparent "circle" the argument reaches at a crucial point. In looking at these points in Chapter 11 Allison prepares the way for an account of the "deduction" apparently carried out in Groundwork III.
The first point Allison makes is that Kant does not really attempt to "prove" the reality of freedom but only the need to "presuppose" it (thus disagreeing with the view of Karl Ameriks who assimilates the argument of Groundwork III to certain passages from lectures in the 1770s). The "presupposition" in question is a necessary one in the sense that morality expresses a law for every rational being as such and so its principle must be bound up in an a priori fashion with the will of such a being. One of the reasons for taking this to be true is that it is requisite rationally to be able to act and one does so under the "idea" of freedom. The "idea" in question is understood by Allison to be freedom in the sense of transcendental spontaneity, the ability, that is, to begin a series absolutely. However this is not equivalent for Allison to the claim that it is necessary to "believe" that one is free or to the fictive claim that this freedom is "heuristic". Rather the idea in question is one which is a necessary product of reason and is thus possessed of objective validity.
Not only is this the case but the idea of freedom also has normative force and acting in accordance with it places one in the "space of reasons". The use of this Sellarsian vocabulary is particularly interesting given that Allison connects the question of freedom to reason in two respects, both theoretical and practical. The understanding is the source of spontaneous grasp of truth (as given in the German for "concept") and it does this in a rule-governed way which is part of its internal operation. Similarly freedom in a practical sense is a product of the internal operation of the will. However whilst Kant's argument, as construed by Allison, appears to lead at this point to the conclusion that there is operative a practical reason whose "reality" we can show, the argument instead takes the turn that leads towards the "circle" that stops its progression in the manner that appears obvious.
Allison's account of the move the argument of Groundwork III takes at this point is grounded on the view that all that has been established up until now is a conditional claim. Freedom has not, as yet, been shown to be actual and the consciousness of autonomy is not one whose binding validity has been shown. So the establishment of the supreme principle of morality has not been achieved and thus the reason for departing from empirical interests has not been conclusively given. This is why Kant speaks now (at Ak. 4: 453) of a "hidden circle" having been apparent in the argument up to this point. Kant's reference to this "circle" is one that has puzzled many including Paton whose commentary Allison cites as a case of misrepresentation of Kant's argument. Allison understands the "circle" to consist in an inference from freedom to autonomy or from negative to positive freedom. However this does mean that Kant was not previously really guilty of arguing in a "circle" but only of begging the question in the sense of taking freedom to have an immediate certainty.
In preparing the way for the resolution of the "circle" in question Kant discusses the notion of "two standpoints" and the rest of Allison's chapter is devoted to looking at the way these standpoints are characterised in Groundwork III. This distinction is one that has to be shown not to be merely an ad hoc device and Kant aims also to show that it is recognised by common understanding although the latter claim is regarded by Allison as dubious. The account of the distinction between appearances and things in themselves is drawn crudely enough in Groundwork III however and it may be, as Allison suggests, that the reason for this crudity is precisely to make the distinction one that can be related to "common understanding". It does, however, also include the distinction between two aspects of the agent, one that certainly seems at variance with "common understanding" but which is justified to it by means of the difference between active and passive aspects of the self. The active element includes the sense of spontaneity in the production of ideas, a capacity not sensibly conditioned. However the question of whether this consciousness is illusory has to be addressed. This is where the claim that all Kant is showing is that freedom is a necessary "presupposition" comes in for Allison since the presupposition is one that we have a warrant for adopting inasmuch as we consider ourselves as members of the intelligible world. This provides, on Allison's reading, a basis for claiming a "deduction" of the "moral law" though not the categorical imperative given his commitment to a "double deduction" reading.