“It is our capacity for freedom or, in [Kant’s] words, to “set ends” – that is, to think and act on the basis of considerations (“reasons”) that once can reflectively endorse – that is central to Kant’s account of human reason. Though at time he describes this capacity as our “spontaneity” and suggests it discloses our membership in a noumenal world, the core idea, I believe, is the idea that freedom, and hence reason, are irreducibly normative concepts.” (Kenneth Baynes, Habermas’s “Kantian pragmatism” in The Cambridge Companion to Critical Theory, pp. 194-218, here p. 196).
So freedom and reason are normative concepts, but in what sense? I think Brandom describes this aspect of reason and freedom better:
“One of Kant’s most basic ideas is that what distinguishes our judgments and actions from the responses of merely natural creatures is that they are things we are in a distinctive way responsible for – that they involve the undertaking of commitments. He understands judging and acting as essentially discursive activities – that is, as consisting in the applications of concepts. And he takes concepts to be rules: rules that specify what one has committed oneself to, what one has become responsible for, in producing a judgment or action.” (Pragmatics and Pragmatisms, in Hilary Putnam: Pragmatism and Realism, pp. 40-58 here p. 49).
To be able to reason and to be free is to be responsible for what we claim, to be able to undertake commitments. To follow rule is necessarily normative in the sense that it implies a capacity to violate rules and (or comply with them willingly). Thus the normativity of reason implies our ability to reflect, to detach from what is given, and to be able to do and think otherwise. However we must give reason for this 'otherwise' as normativity implies commitment and responsibility and not arbitrariness.
One of Kant's greatest mistakes was to attach this normatively to his account of the way we acquire knowledge of objects. Allison describes this in what follows:
“. . . it is necessary to realize that what is required for objective representation is not simply the de facto presence of a rule governed unity of representation in consciousness . . . but the thought or conceptual recognition of this unity. In other words, this unity must not only be in a single consciousness, it must be for that consciousness in the sense that mind must be able to represent it to itself or, equivalently, to recognize it as such. This reflexive dimension of cognition follows directly from the normative nature of the claim of objective connection. For unless the mind could think, that is, represent to itself or recognize the rule-governedness of the unification. It would remain a merely contingent, causally conditioned connection of mental states without any epistemic significance.” (Henry E Allison, (1995) "On Naturalizing Kant's Transcendental Psychology", Dialectica, 49(2-4, pp. 335-351, here pp. 343-344).
Habermas like Kant relates normativity to objectivity but dissociates the analysis of objectivity from the level of perception and brings it to the level of communicative understanding.