Note: Moving to the front (from March 7) due to recent comments
1) In the course of the 19th century within the history of Philosophy we witness a challenge emerging to the naturalism prevailing since the early modern times. In the Kantian philosophy we find an assertion of the Platonic and rationalist belief in the “otherworldly” character of the key modern concepts like reason, freedom and reflection. For sure, Kant gave crucial concessions to the naturalism in general. He accepted its overall detranscendentalising thrust. However he insisted on preserving something crucial from this overall detranscendentalising project. The concepts of freedom and reason cannot be sustained within a thoroughgoing detranscendentalising trust of the modern philosophy. One needs to make room for a transcendental/intelligible realm where ‘reason’ and ‘freedom’ can be located. This resulted in two crucial premises on which Kantian idealism is based.
1a) Reason is not a thing of ‘this world.’ It cannot be reduced to or emerge from within it. There is a crucial distinction between empirical/natural and rational realm. It is manifested in Kant’s distinction between freedom and nature in a binary way. In sum, for Kant empirical and rational orders are exclusive.
1b) Reason requires a subject, a subject with a possibility of freedom. A subject is not only part of the ‘natural’ order but also a member of the rational order. It is through this ‘dual’ character of the subject that the natural order and rational orders are interrelated.
3) Habermas’ unique synthesis is Not unlike Kant, who at the time, had tried to combine the opposing tendencies of empiricism and rationalism, Habermas also aims to combine naturalism/empiricism and idealism/anti-naturalism.
4) On the one hand Habermas fully agrees with naturalism/empiricism in general on the issue of the ‘desublimation’ and ‘detranscendentalisation’ of the reason, freedom and our understanding of the world in general. He critiques idealism and anti-naturalism on this account throughout his writings. In this regard Habermas’ critiques the notion of the transcendental subject among other notions.
5) On the other hand Habermas also holds fast to the key idealist assumption that ‘reason’ cannot be reduced to the ‘empirical’ and it is important to maintain the transcending powers of reason. He also insists that reason and freedom are closely related and he insists on that in order to preserve the transcending power of reason. We need to hold to the notion of subject capable of accomplishments a subject that is not merely a ‘cultural dope.’ Thus Habermas aims to preserve the conception of a subject capable of accomplishments even when he accepts the critique of subject aimed at the Kantian tradition.
6) Habermas maintains that the naturalist project of desublimation and detranscendentalisation of reason can be combined with the Kantian project of preserving the transcending powers of reason. Habermas’ crucial, central and unique insight is that the Kantian distinction between empirical and transcendental can be preserved without ascribing to the Kantian distinction between empirical and intelligible world/order. This would result, claims Habermas, in a new synthesis where we would be able to combine the best of empiricism and idealism, naturalism, and anti-naturalism without however ascribing to their shortcomings. Habermas calls this position a weak naturalism in his most recent writings.