  To support his conception of communication action, Habermas must specify the mechanism that makes rationally motivated agreement possible. Toward that end, he argues for a particular account of utterance meaning as based on “acceptability conditions,” by analogy to the truth-conditional account of the meaning of sentences. But rather than linking meaning with representational semantics, Habermas takes a pragmatic approach, analyzing the conditions for the illocutionary success of the speech act. According to the core principle of his pragmatic theory of meaning, “we understand a speech act when we know the kinds of reasons that a speaker could provide in order to convince a hearer that he is entitled in the given circumstances to claim validity for his utterance—in short, when we know what makes it acceptable” (1998b, 232). With this principle, Habermas ties the meaning of speech acts to the practice of reason giving: speech acts inherently involve claims that are in need of reasons—claims that are open to both criticism and justification. In our everyday speech (and in much of our action), speakers tacitly commit themselves to explaining and justifying themselves, if necessary. To understand what one is doing in making a speech act, therefore, one must have some sense of the appropriate response that would justify one's speech act, were one challenged to do so. A speech act succeeds in reaching understanding when the hearer takes up “an affirmative position” toward the claim made by the speaker (TCA 1: 95–97; 282; 297). In doing so, the hearer presumes that the claims in the speech act could be supported by good reasons (even if she has not asked for them). When the offer made by the speaker fails to receive uptake, speaker and hearer may shift reflexive levels, from ordinary speech to “discourse”—processes of argumentation and dialogue in which the claims implicit in the speech act are tested for their rational justifiability as true, correct or authentic. Thus the rationality of communicative action is tied to the rationality of discourse, more on which in section 3.2.