Critique of Cognitive Parallelism

Habermas’s discourse ethics implies a cognitivist assumption that normative claims are justifiable on the basis of communicative reason. This assumption makes an analogy between factual claim to truth and normative claims to rightness. In the communicative action, we can defend or repudiate the legitimacy of one’s normative statement, just as we can defend or repudiate the correctness of one’s factual statement in the instrumental action. Cognitive parallelism is the very foundation of Habermas’s argument. Then, the question is, is this parallelism plausible?