 Work on the ontology of jazz has centered around the nature of improvisation, particularly the relation between improvisation and composition (Alperson 1984, 1998; Valone 1985; Brown 1996, 2000; Hagberg 1998; Gould &amp; Keaton 2000; Sterritt 2000; and Young &amp; Matheson 2000; Bresnahan 2015; Love 2016; Magnus 2016). This has been a useful reminder that not all music is the performance of pre-composed works (Wolterstorff 1987: 115–29). However, it must be noted that improvisation can occur within the context of such a work, as in the performance of an improvised cadenza in a classical concerto. Some have argued that there is not as significant a distinction between improvisation and composition as is usually thought (Alperson 1984). Others have argued that all performance requires improvisation (Gould &amp; Keaton 2000). Yet others restrict the possibility of improvisation to certain kinds of musical properties, such as “structural” rather than “expressive” ones (Young &amp; Matheson 2000). However, the arguments are not compelling. Usually they turn on equivocal use of terms such as “composition” and “performance”, or beg the question by defining improvisation in terms of deviation from a score or variation of a limited set of “expressive” properties.