Jürgen Habermas is known in the world of analytic philosophy primarily as a moral and political philosopher. He has striven against a slide which has often seemed plausible and tempting for modern thinkers, that towards a certain relativism or subjectivism in morals. The difficulty of establishing firm ethical conclusions in the midst of vigorous debate among rival doctrines, particularly when these disputes are contrasted to those among natural scientists can all too easily push us to the conclusion that there is no fact of the matter here, that ethical doctrines are not a matter of knowledge, but only of emotional reaction or subjective projection, that the issues here are not cognitive.
Habermas from the very beginning set his face against these non-cognitivist views. There can be ethical knowledge. But he wished also to break with a long-hallowed notion of what this knowledge must consist in, that which we find in the traditions which go back to Plato and Aristotle. According to these, ethical knowledge has for its object human nature, or the nature of things. In other words, it is grounded in some normative picture of what humans are like, or else of their place in the universe. According to Habermas, it was the discredit of these “metaphysical” views which gave colour to non-cognitivism in the first place. In order to refute subjectivism, morality needs another kind of rational basis.
The alternative route which he explored was that which makes the rationality of ethical conclusions a function of the rationality of the deliberation which produces them. A deliberation is rational if it meets certain formal requirements. This is, of course, the route which was pioneered by Kant. But Habermas made a revolutionary change in this tradition. Whereas for Kant the principal criterion of a rational and therefore defensible deliberation was that it was sought universalizable maxims, for Habermas the very notion of deliberation is transformed.