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
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 s 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 .
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.
