Summary The dispute about positivism in German sociology dealt basically with the question, whether we can know what we ought to do or whether we must be content to decide what we want to do. Habermas questioned the distinction which positivists and decisionists draw between science on the one hand and ethics on the other. Later he proposed his own notion of knowledge about reality and along with it a notion of normative or ethical knowledge and he claimed the two (...) notions were comparable. He developed the first notion in the form of a consensus theory of the truth of statements and the second one in the form of a consensus theory of the rightness of norms and values. The consensus theories are examined and it is shown that both are untenable for various reasons. (shrink)