Habermas often speaks as though the question of the rationality of a worldviews as a whole cannot be judged within the parameters of a post metaphysical concept of rationality. However this is true only regarding the substantive portion of any worldview is concerned (its conception of good life for example). The same does not apply to the formal character of a worldview. Thus two worldviews can be judged and compared as a whole as regard to their formal-prgamtic rational potential. Hence on this level we can judge one worldview as less or more rational than other or can even judge some worldviews as irrational if they lack the basic formal-pragmatic concepts!
As Habermas puts it:
“The rationality of worldviews is not measured in terms of logical and semantic properties but in terms of formal-pragmatic basic concepts they place at the disposal of individuals for interpreting their world. We could also speak of the “ontologies” built into worldviews, providing that this concept, which stems from the tradition of Greek metaphysics, is not restricted to a special world-relation that is, to the cognitive relation to the world of existing things [Seienden]. There is no corresponding concept in philosophy that includes relations to the social and the subjective worlds as well as to the objective world. The theory of communicative action is also meant to remedy this lack.” (TCA I: p. 45).
Thus the modern worldview is superior to pre modern worldviews because it possesses richer formal-pragmatic basic concepts.
“On the other hand, worldviews differ form portraits in that they in turn make possible utterances that admit of truth. To this extent they have a relation, albeit indirect, to truth . . . . Owing to their reference to totality, worldviews are indeed removed from the dimension in which judgment of them according to criteria of truth makes sense; even the choice of criteria according to which the truth of statements is to be judged may depend on the basic conceptual context of a worldview . . . worldviews can be compared with one another not only form the quasiaesthetic and truth-indifferent standpoints of coherence, depth, economy, completeness, and the like, but also form the standpoint of cognitive adequacy. The adequacy of a linguistically articulated worldview is a function of the true statements that are possible in this language system.” (TCA I: 58-59, italics in the original).