Perfect fourth
Encyclopedia : P : PE : PER : Perfect fourth
| Inversion (music)>Inverse | perfect fifth | |
|---|---|---|
| Name | ||
| Other names | diatessaron | |
| Abbreviation | P4 | |
| Size | ||
| semitone>Semitones | 5 | |
| Interval class | 5 | |
| Just intonation>Just interval | 4:3 | |
| Cents | ||
| Equal temperament | 500 | |
| Just intonation | 498 | |
The perfect fourth or diatessaron, abbreviated P4, is one of two commonly occurring musical intervals that span four diatonic scale degrees; the other being the augmented fourth, which is one chromatic semitone larger. The prefix perfect identifies it as belonging to the group of perfect intervals, so called because of their extremely simple pitch relationships resulting in a high degree of consonance. The perfect fourth's inversion is the perfect fifth.
Its most common occurrence is between the fifth and upper root of all major and minor triads and their extensions.
A perfect fourth in just intonation corresponds to a pitch ratio of 4:3, while in an equal tempered tuning, a perfect fourth is equal to five semitones, a ratio of 1:25/12 (approximately 1:1.3348), or 500 cents, about 1.955 cents wide.
The perfect fourth is a perfect interval like the unison, octave, and perfect fifth. In common practice harmony, however, it is actually considered a dissonance in certain contexts. Specifically, it is considered consonant when heard in its most common position as detailed above; but dissonant when built upon a chord's root. In such a position, the interval's upper note almost always temporarily displaces the third of any chord, and is then called a suspended fourth.
Conventionally, the strings of a double bass and a bass guitar are tuned by intervals of perfect fourths, as well as all strings but one of a guitar.
See also
| Diatonic intervals | [http://encycl.opentopia.com/ edit ] |
| Perfect : unison (0) | fourth (5) | fifth (7) | octave (12) | |
| Major : second (2) | third (4) | sixth (9)| seventh (11) | |
| Minor : second (1) | third (3)| sixth (8)| seventh (10) | |
| Augmented/Diminished : tritone (6) | |
| semitones of equal temperament are given in brackets | |
External links
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