The three families of error
- Parallel (consecutive): two voices form a fifth (or an octave, or a unison) and move in the same direction to another fifth (or octave). Example: C4/G4 → D4/A4.
- Hidden (direct): two voices arrive by similar motion at a perfect consonance from a different interval. Example: E4/C5 (sixth) → G4/D5 (fifth). The fifth is not preceded by a fifth, but the ear hears it as if the voices had traveled there together.
- By contrary motion (antiparallel): two consecutive fifths or octaves reached by contrary motion, such as C4/G4 → G3/D5 (fifth and twelfth). In strict two-voice counterpoint they are forbidden just like parallels.
Why they are avoided
Two voices in consecutive fifths or octaves lose their independence: the octave melts into a doubling, and the fifth creates a single hollow sonority that moves as a block. In counterpoint, whose purpose is to make several autonomous lines audible, this is a flaw. Zarlino was among the first to justify the prohibition in terms of variety; Fux turns it into the four rules of motion.
Special cases in the species
- First species: no parallels, no hidden fifths or octaves, no internal unisons.
- Second species: watch for fifths or octaves on consecutive strong beats. With the cantus D4–G4, the counterpoint A4 B4 | D5 forms two fifths on consecutive downbeats (A4 over D4, D5 over G4): the passing note and the leap of a third are not enough to hide them, and the ear hears them as consecutive.
- Third species: also check the last quarter note of a bar and the first of the next, as well as the first quarter notes of consecutive bars.
- Fourth species: the syncopation does not hide fifths on the weak beats: a chain of 5–6, 5–6 should be avoided if the fifths fall on consecutive preparation beats.
- Three and four voices: hidden fifths and octaves are tolerated between inner voices and, within limits, when the upper voice moves by step; they remain to be avoided between the outer voices.
Examples to correct in C
- C4/G4 → D4/A4 → E4/B4: three parallel fifths. Correction: C4/G4 → D4/F4 → E4/C5 (fifth, third, sixth).
- D4/B4 → G4/D5: a sixth going to a fifth by similar motion, hidden. Correction: D4/B4 → C4/C5, or D4/B4 → G4/E5 (sixth).
- C4/C5 → D3/D4: octaves by contrary motion. Correction: C4/C5 → D4/B4.
How to spot them quickly
- Write the interval numbers under the notes; every adjacent 5–5 or 8–8 pair is suspect.
- For every 5 and 8, check the direction of the two voices on arrival: if it is the same, there is a problem.
- In florid species, mark the strong beats with a dot and also check the succession from dot to dot.
- In four-part writing, check pair by pair: six pairs (S-A, S-T, S-B, A-T, A-B, T-B).
When parallels are a choice
Outside strict counterpoint, parallels are a timbre: medieval organum, Impressionism (parallel chords in Debussy), rock (power chords), orchestral unisons and octaves. The distinction is between doubling (a single line reinforced at the octave or fifth, which counts as one voice) and independent voice leading (where parallels reduce the number of real voices).
Modern application
- Pop vocal arranging: in three-part harmonies the low voice tends to fall into parallel fifths with the melody; move it to a sixth or a third.
- Pads and synths: fixed-position voicings that slide in parallel produce parallel fifths; acceptable as color, but for a more orchestral sound you need proper voice leading.
- Film strings: cellos and basses in octaves are a deliberate doubling, not an error; violins and violas moving in fifths for four bars, on the other hand, sound hollow.
Related topics
Four rules of motion, voice-leading rules, voice leading in pop, first and second species, four-voice species.