The or '''''diatessaron''''', abbreviated '''P4''', is one of two commonly occurring
Musical Interval s 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 Triad s and their
Extensions .
A perfect fourth in , a perfect fourth is equal to five
Semitone s, or 500
Cent s, 2 cents looser (to use a piano tuning term) than the 4:3 perfect fourth.
A helpful way to recognize a perfect fourth is to hum the starting of the Bridal Chorus from Wagner's ''Lohengrin'' ("''Treulich gefuehrt''," the colloquially titled
Here Comes The Bride ), which is a familiar perfect 4th.
The perfect fourth is a perfect interval like the
Unison ,
Octave , and
Perfect Fifth , and it is a sensory
Consonance . In
Common Practice harmony, however, it is considered a stylistic dissonance in certain contexts, namely in two-voice textures and whenever it appears above the bass.
1 If the bass note also happens to be the chord's root, the interval's upper note almost always temporarily displaces the
Third of any chord, and is then called a .
Conventionally, the strings of a
Double Bass and a
Bass Guitar are tuned by intervals of perfect fourths, as well as all but one of the strings of a guitar. It is also a very common
Musical Interval to which
Tom-tom Drum s are tuned.
