“Weak naturalism neither incorporates nor subordinates the “internal perspective” of the lifeworld to the “external perspective” of the objective world. Rather, it keeps these theoretical perspectives separate, connecting them at the metatheoretical level by assuming a continuity between nature and culture.” (TJ: 28)
The unbridgeable gap between the “internal perspective” and the “external perspective” corresponds to the distinction between reason and nature. On the methodological level, Habermas maintains this dualism (more appropriately, this sharp distinction) as his homage to the Kantian insight about the irreducibility of “reason” and “nature,” reason and the space of law. However on the metatheoretical level, Habermas postulates an ontological continuity between nature and reason, hence implying that the methodological distinction has emerged historically from the evolution of learning processes which trace their origin back to/in nature. This is Habermas’ homage to Darwin.
Note: This post should be read in the context of the previous posts (here and here)