Consecutive Fifths - Related Progressions - Hidden Consecutives

So-called hidden consecutives, also called direct or covered octaves or fifths, occur when two independent parts approach a single perfect fifth or octave by similar motion instead of oblique or contrary motion. A single fifth or octave approached this way is sometimes called an exposed fifth or exposed octave. Conventional style dictates that such a progression be avoided; but it is sometimes permitted under certain conditions, such as the following: the interval does not involve either the highest or the lowest part, the interval does not occur between both of those extreme parts, the interval is approached in one part by a semitone step, or the interval is approached in the higher part by step. The details differ considerably from period to period, and even among composers writing in the same period.

An important acceptable case of hidden fifths in the common practice period are horn fifths. Horn fifths arise from the limitation of valveless brass instruments to the notes of the harmonic series (hence their name). In all but their extreme high registers, these brass instruments are limited to the notes of the major triad. The typical two-instrument configuration would have the high instrument playing a scalar melody against a lower instrument confined to the notes of the tonic chord. Horn fifths occur when the upper voice is on the first three scale degrees.

Traditional horn fifths actually come in pairs. Begin with the upper instrument on the third scale degree and the lower instrument on the tonic. Then move the upper instrument to the second scale degree and the second instrument down to the fifth of the chord. Because the distance from 5 up to 2 is a perfect fifth, we have just created a hidden fifth by descending motion. The first instrument can then complete its descent to 1 as the lower instrument moves to 3. The second hidden fifth of the pair is obtained by making the upward maneuver a mirror image of the downward maneuver. The reason that these fifths are acceptable is that one would otherwise have to commit the gaffe of doubling the third scale degree at the octave, or else forbid the low instrument from using that degree (therefore giving him only the tonic and fifth to work with). Although traditional horn fifths come in pairs and in passing, the acceptability of horn fifths has been generalized to any situation of hidden fifths where the top voice moves by step.