"[Even after the detranscendentalisation of the knowing and acting subject] the problem of naturalism does not simply vanish into thin air. It merely arises in another way for those theories that do indeed being with questions posed transcendentally, yet do not get stuck cutting the intelligible off from the phenomenal once for all. These theories must find answer to the question of how Kant can be reconciled with Darwin. It seems to me that it has been clear since Marx that the normative content of modernity can be taken up and preserved even and especially under materialistic premises. "Nature in itself" does not coincide with objectivated nature. What Marx has in mind is the emergence in natural history of the sociocultural form of life Homo sapiens, which goes beyond physcially objectified natura naturata to conceptually include, as it were, a piece of natura naturans. A naturalism of this sort need not be accompanied by an objectivistic self description of culture, society, and the individual." (PT: 20).
In the light of the above we must ask how the problem of detranscendentalisation is related to the problem of naturalism and how Habermas’ project of transcendence from within is related to his project of weak naturalism?
The problem of detranscendentalisation is to save the transcending power of reason. In this sense problem of detranscendentalisation is to avoid contextualism. Detranscendentalisation places the context and its understanding at the heart of our understanding the problem of rationality. Contexts are by definition particular and the problem of detranscendentalisation then becomes preserving the transcending powers of reason within this inevitable contextualisation. Thus the project of transcendence form within aims at proving and preserving the transcending powers of reason which is akin to showing that reason has ability to transcend the context in which it is inevitably situated and hence of transcending particularity, from within.
The problem of naturalism is akin to the problem of detranscendentalisation in the sense that as in the case of detranscendentalisation the transcending power of reason has to be proven and preserved in the face of a particularity (in this case nature). The problem of contextualism arises with a thorough going detranscendentalisation while the problem of naturalism arises with theory of evolution and a thorough going materialism (hence) Habermas mentions Kant in conjunction with Darwin. Thus the problem of naturalism is to reconcile Kant with Darwin, i.e. to show how we can believe in a through going naturalism without forsaking the transcending powers of reason (i.e. the task of weak naturalism).
Detranscendentalisation in itself does not entail reconciliation with nature or reconciliation of Kant with Darwin because we can suppose detranscendentalisation and still think that nature and reason belong to two different realms. One can maintain that reason emerges from social and that nature is non social (something Habermas also maintains in one form), and hence there is no compulsion to think that reason (social thing) have evolved from nature (a non social thing). Thus one can maintain a dichotomy between nature and reason without maintaining a dichotomy between the realm of intelligibility and realm of social. In other words one can be an anti naturalist in the sense of maintaining that reason has not evolved form nature without being a transcendentalist. Thus detranscendentalisation is compatible with anti naturalism.