We have observed in chapter 5 that reversal, as a formal concept, is apparent on several compositional levels in Purcell's sonatas. Subjects may be devised as pitch palindromes (as in the Vivace of Z. 791), and when structural features within movements are abstracted into labels they sometimes create palindromes (as was the case with the combinatorial permutations in the Largo of Z. 802). On a higher level of multi-movement form, movement types can be arranged in reverse, with or without a clear da capo effect (as in Z. 794), and the order of material appearance may be reversed toward the end of the piece in a way that resembles arch form (as in Z. 792).

However, these reversals are not necessarily the strongest influence on the overall form of movements. Only in those works cast in arch-form structures did we observe the direct influence of reversal on the form. Otherwise, palindromic subjects or order of the entering parts may have very little influence on the overall form. To take an example, an exchange of the violin parts halfway into a movement, while it may upset the chiastic structure of the movement, does not necessitate essential alterations to what the movement sounds like. When reversal applies to the order of material, it exerts direct influence on the form, and this happens when Purcell combines chiastic structures with fugues that have more than one subject. Of the various rhetorical figures surveyed in chapter 5, commutatio is the closest in scale and in nature to thematic chiasmus patterns of that kind.

Let us first analyze the second section of the G minor Fantazie from Locke's Consort of Four Parts (Suite no. 5, example 6.1). On the surface, the use of three distinct subjects in this section (labeled “A,” “B,” and “C” in example 6.1) and the consistent imitative texture make “triple fugue” the most appropriate term. This, however, helps very little in the distinction between different stages of the unfolding of the music—the term “triple fugue” says nothing of the structural division of the movement into an opening procedure (such as the n-fold rotation), a closing procedure (such as a close), or a middle episode of the kind one may find in many Purcellian canzonas.