Readers of Tempo will already be familiar with some of Xenakis's basic ideas on music, from the abridged translation of some of his writings published in Tempo 78. These theories have provoked a good deal of comment, and it is worth considering his latest work, Nuits, in relation to the implications of them. The mainstay of the theoretical substructure underlying Xenakis's textural style is his critique of musical ‘causality’, i.e. the thematic process in music from the classical style right up to the total thematicism of integral serialism. On the analogy of the sciences, where the causal principle has been superseded by probability theory, the development of occidental music beyond the impasse of total serialism can only be ensured, Xenakis contends, by means of a ‘rationalisation of chance’ articulated in generalised musical textures, the morphology of which is governed by statistical laws.