- Howard Mayer Brown
- , revised by Claus Bockmaier
(1) The 15th- and 16th-century term for a beat, i.e. a unit of time measured by a movement of the hand, first discussed in detail by Adam von Fulda (De musica, 1490). One tactus actually comprised two hand motions, a downbeat and an upbeat (positio and elevatio, or thesis and arsis). Each motion was equal in length in duple time (tempus imperfectum); in triple time (tempus perfectum) the downbeat was twice as long as the upbeat.
In theory the tactus in 16th-century music measured a semibreve of normal length (integer valor notarum), a breve in diminution (proportio dupla), and a minim in augmentation. Gaffurius (Practica musice, 1496) wrote that one tactus equalled the pulse of a man breathing normally, suggesting that there was an invariable tempo then of M.M. = c60–70 for a semibreve in integer valor...