Alex Rosenberg writes:
...we may characterize naturalism in philosophy as follows:
1. The repudiation of 'first philosophy'. Epistemology is not to be treated as a propaedeutic to the acquisition of further knowledge.
2. Scientism. The sciences-from physics to psychology and even occasionally sociology, their methods and findings - are to be the guide to epistemology and metaphysics. But the more well established the finding and method the greater the reliance philosophy may place on it. And physics embodies the most well established methods and findings.
3. Darwinism. To a large extent Darwinism theory is to be both the model of scientific theorizing and the guide to philosophical theory because it maximally combines relevance to human affairs and well foundedness.
Naturalism in the philosophy of science adds another element to this credo:
4. Progressivity. Arguments from the history of sociology of science to the non-rationality, or nor cumlativity, or non-progressive character of science, are all either unsound and/or invalid.
A Field Guide to Recent Species of Naturalism
Just a quick note with reference to Habermas:
Speaking very roughly I would say Habermas would accept the first proposition wholeheartedly as far as Epistemology is conceived as a project of first philosophy. He would probably also accept the 4th proposition with may be some rephrasing. However he would reject 2 & 3. He would say about (2) that it is not naturalism it is reductionism. Scientific method and Sciences are tiny part of "nature and knowledge about nature". As for (3) he would say what we need is to combine Kant and Darwin (see
Truth and Justification, introduction)
Professor Rosenberg's above paper can be downloaded from here
Also few other papers by Rosenberg are available for download from his site Alex Rosenberg
Also an interesting course on naturalism with links to some very interesting papers Naturalism Course Schedule