So far throughout this study, time signatures havealways been described either as directlyproportional to each other or in a 1.5:1relationship. This implies a rather rigidmathematical system, without much “wiggle room,” asit were. This chapter, however, will describe amajor exception to this mathematically linkedterraced tempo system: when sections of acomposition were written in stylus phantasticus, these wereunderstood to have a slower tactus rate than thepassages surrounding them. This was accomplishedmainly by shifts of dominating note values, fromfaster note values in stylusphantasticus implying a slower tactusrate, to sections with slower note values implying afaster tactus rate. But the implications of thisassertion go deeper than this: the use of stylus phantasticus alsomeans that even when moving directly from or into asection that should normally be strictlyproportional, the proportional section has aslightly faster tactus rate than the stylus phantasticus section.In a sense, then, stylusphantasticus sections are removed fromproportional relationships.

To understand how such conclusions can be drawn, thefollowing points will be addressed:

• 1. THE DEFINITION OF STYLUS PHANTASTICUS. Here, we willreview what Athanasius Kircher and JohannMattheson taught concerning stylus phantasticus, and then narrowthat definition further to a very specific texturefor the purposes of tempo determination.

• 2. EVIDENCE FOR A SLOWER TACTUS RATE IN STYLUS PHANTASTICUS. Thisinquiry will examine changes involving stylus phantasticus withinduple meter, then within the proportional meters,and finally within the context of a cantus firmus.

Performer's Corner

While Baroque authors gave a broader definition ofstylus phantasticus,in this study its definition is narrowed to aparticular texture: it almost always shows fasternote values than the surrounding sections, often hasan elastic pulse, and is a free improvisatory styledesigned to amaze with technical brilliance. Asalready described above, the most important aspectof stylus phantasticusis that its tactus rate was slower (by a degreechosen by the performer) than that of neighboringsections. This is mainly because of its suddenchange in faster note values. For example, when astylus phantasticussection in sixteenth and thirty-second notes (oreven faster) moves out of a fugue running in eighthnotes, the faster note values of the stylus phantasticus requirethe underlying tactus rate to slow down.