Third Species

figure 1	figure 2	figure 3
passing note	dissonant 4th crotchet	cambiata formula

IN the third species the counterpoint requires four crotchets (quarter notes) to be set against each note of the cantus firmus. The additional rules for this species are:

• The first note of each bar must be consonant with the CF.
• The second note may be dissonant if both the first and third notes are consonant and are respectively a step above and a step below the second note, or are a step below and a step above the second note (figure 1). In other words the second note may be a dissonant passing note between consonances on the first and third beats.
• Likewise, the third note may be dissonant if it is a passing note between consonances on the second and fourth beats.
• In the same way, the fourth note may be dissonant if it is a passing note between consonances on the beats immediately before and after it (figure 2).
• The second note may be dissonant when it is used in the 'cambiata' formula (figure 3). In this case the first note is consonant, the dissonant second note is a step below the first, the third note is consonant and a third below the second note, and the fourth note is a consonance a step above the third note. In practice this will mean the intervals formed above the CF are 8-7-5-6.

An example from Gradus

• Note the use of dissonant passing notes on the second crotchet in bars 2, 3, 6 & 9, on the third crotchet in bars 1 & 4, and on the fourth crotchet in bars 5 & 7.
• Only a single unison is used (bar 6).
• The cambiata formula may be used as an alternative to the closing formula shown in the example.