Recall that in weak naturalism Habermas’ aim is to explain the transcending power of reason without reverting to the Kantian dichotomy between reason and nature and without reverting to the Kantian two realm dichotomy. In other words the aim of weak naturalism is to explain the transcending powers of reason within overall naturalistic framework. Quine and Heidegger fail in this although on different grounds.
Quine’s strong naturalism cannot account for the transcending powers of reason and consequently the ability of subjects capable of speech and actions to accomplish things rationally. Quine’s theory fails because it does not take seriously the Kantian insight about the normativity and uniqueness of human reason seriously. It does not feel any need to differentiate between the space of reason and the space of causality. However this cannot explain our ability to learn form mistakes as learning is closely related to grounds (reasons). Causality cannot explain the learning process (as well as unlearning process).
On the other hand Heidegger’s fault is that he ignores two important facts: a) on the one hand he ignores causality altogether. Causality is devoured by the all consuming powers of linguistic world disclosure. b) The linguistic world disclosure also devours the ability of subjects capable of speech and act to rationally assess and revise the given meaning. These revisionary powers have two aspects: a) on the one hand given meaning is the condition for subjects to understand and raise validity claims in the first place. In this sense it is an enabling power. b) Thus it is impossible for subjects to transcend their linguistic background in to to. In fact it would be undesirable given this background is the condition of the possibility for anything subjects are capable of doing and saying. Thus the conditions of possibility of understanding and meaning are not only limiting conditions they are also enabling conditions. They enable the formation of subjects that are capable of initiation, accomplishment and revision. Thus though the lifeworld and linguistic background is immune from objectification the process within disclosed world can lead to the indirect revision of the very conditions of possibility sometime partially sometime radically. Thus the revisions are the indirect result of accomplishments of subjects capable of speech and action but they are not the direct subjects of these processes for two reasons: a) Changes in lifeworld are affected by the plurality of subjects and their interactions. So we cannot reduce changes in lifeworld to the intentions of subjects even if their attitudes play a role in the change. b) Even with a) there is no total change as lifeworld and language cannot be objectified in to to. There can be radical changes but there is no overall subject of these changes.
Heidegger though emphasises the disclosive power of language he does not emphasise with equal force the enabling possibilities within the world disclosed and does not in turn relate the disclosive function of language with these enabling possibilities.
Finally both Heidegger and Quine ignore our non linguistic non conceptual non causal contact with the reality. The recalcitrant reality with which we are in direct contact resist both the disclosing function and our accomplishments within it. Both have to prove themselves in the face of this pro-active reality.