Throughout his career, Wittgenstein propounded two main claims concerning nonsense. First, all metaphysics is nonsensical. The proper task of philosophy is not to answer metaphysical questions by producing theses, doctrines or theories, but to show that they rest on conceptual confusions. Second, ‘the negation of an a priori proposition’, for example, ‘7 + 5 = 12’ or ‘Some objects are red and green all over at the same time’, is not a necessarily false proposition, but a nonsensical combination of signs (see PI §§251–2). By the same token, the a priori or necessary propositions themselves do not exclude a genuine possibility, since in their case no such possibility can meaningfully be specified (TLP 3.03–3.05; AWL 139–40, 165–66). Instead, the later Wittgenstein argued, such propositions ban a certain combination of words as meaningless from our language. Necessary propositions are not necessary truths (strictly speaking), but norms that exclude certain sign combinations from our language.

Both of these ideas have been vigorously contested by mainstream analytic philosophers. In recent years, Wittgenstein's conception of nonsense has also been the central focus of the proponents of a ‘New Wittgenstein’ (Crary and Read 2000). Two claims set the New Wittgensteinians apart. The first is a reading of the Tractatus. In the final sections, Wittgenstein condemns the propositions of the Tractatus itself as nonsensical (6.54–7). According to a standard interpretation, his reason was that these propositions try to express truths about the essence of language which, by Wittgenstein's own lights, cannot be expressed in philosophical propositions, but which manifest themselves in non-philosophical propositions properly analysed. According to the New Wittgensteinians, by contrast, the Tractatus does not consist of illuminating nonsense, nonsense that vainly tries to hint at ineffable truths, but of ‘plain nonsense’ (Diamond 1991, 181; James Conant 1992, 198), nonsense in the same drastic sense as gibberish like ‘ab sur ah’ or ‘piggly tiggle wiggle’. The purpose of the exercise is therapeutic. By producing such sheer nonsense, Wittgenstein tries to unmask the absurd nature of philosophy and to wean us off the temptation to engage in it.

The second claim is an interpretation of Wittgenstein's conception of nonsense. According to the New Wittgensteinians, his conception of nonsense, both early and late, was ‘austere’ rather than ‘substantial’ (Crary and Read 2000, 12–13; Diamond 1991, 111–12; 2000, 153, 165; James Conant 2002, 380–83).