I have posted several times on the pragmatist conception of Knowledge and its significance for Habermas. Pragmatist conception of Knowledge acquires significance for Habermas mainly in the context of his weak naturalism. The question arises what specific role a pragmatist conception of knowledge fulfils for Habermas' weak naturalism. I have provided few clues before. However here are two main functions of the pragmatist conception of knowledge for Habermas' weak naturalism. I provide the relevant quotes below (to be elaborated later).
“If we presuppose [the] pragmatic conception of knowledge, we can opt for a naturalism that preserves the transcendental difference between the world and what is innerworldly, in spite of detranscendntalisatization.” (TJ: 27).
The meaning of the quote is clear even if the full logical analysis of the links is to be provided. Weak Naturalism is supposed to provide the resources that allow us to maintain the Kantian distinction between "empirical" and "transcendental" even after the detranscendentalisation. However for Habermas this can only be done if we adopt a pragmatist conception of knowledge.
“The world of the natural environment is constituted as nature that is objective “for us” by means of the same forms of social labor whereby the physical “material transformation” between society and its material substrate is accomplished. The next step is to interpret this materialist connection between knowledge and labor naturalistically. At the level of sociocultural development, natural evolution is supposed simultaneously to produce “subjective nature,” that is , the organic endowment ofHomo sapiens, and the conditions under which he has cognitive access to what is to him “objective nature.” However, if there is a rigid, that is, inescapable, correlation between objective nature and the possible forms of coping with nature that are determined by subjective nature, then the constitution of a “nature in itself” can only be the result of the glimpse behind the stage set by human mind.”
But the above dilemma can be avoided if we adopt the pragmatic conception of knowledge:
“The aporias we face as a result of detranscendentalisation seem to show that the transcendental formulation of the problem cannot be separated unscathed form the assumption of transcendental idealism. However, the paradoxical consequences result not so much form a pragmatist transformation of the transcendental approach as from the representational model of knowledge to which Kant himself subscribed. A nonclassical form of epistemological realism, which must be accepted in the wake of the linguistic turn, can be combined with a “weak” naturalism without relinquishing the transcendental pragmatic approach.” (TJ: 22).
Habermas wishes to maintain the Kantian distinctions between 'subjective nature', 'objective nature' and 'nature in itself' even after the detranscendentalisation. According to critics (like McCarthy and Whitebook) this leads to contradictions and aporias. Habermas retorts that the said aporias result because of the representational model of knowledge that is presupposed. If we move on to a pragmatist conception of knowledge the aporias vanish away. The function of the pragmatist conception of knowledge here is that it helps maintain a distinction between 'objective nature' and 'nature in itself' which is important for Habermas' weak naturalism.