Perfect fifth

In music theory, a perfect fifth is a special distance between two notes. One note vibrates exactly 1.5 times faster than the other note. This creates a pleasant and natural sound that has been used in music for a long time.

In classical music from Western culture, a perfect fifth is found between the first and fifth notes of any scale. For example, in the scale that starts with C, the note G is a perfect fifth above C. This interval sounds harmonious and stable.

The perfect fifth is more pleasing to the ear than most other intervals, except when two notes are the same pitch (a unison) or exactly eight notes apart (an octave). It is a key part of many chords and is used in many songs and pieces of music. Even in simple melodies like "Twinkle, Twinkle, Little Star", the perfect fifth can be heard between the first and second "twinkle."

Alternative definitions

The term perfect helps us identify the perfect fifth as part of a group called perfect intervals. This group includes the unison, perfect fourth, and octave. These intervals are special because they have simple relationships between notes and sound very harmonious together.

Perfect intervals are also defined by their ability to stay natural when their positions are reversed, called inversions. This means they remain the same type of interval even when flipped. In music, the perfect intervals are the unison, fourth, fifth, and octave. They can also be described using simple ratios of numbers, like 3:2 for the perfect fifth.

Other qualities

Besides the perfect fifth, there are two other types of fifths. The diminished fifth is a little smaller than a perfect fifth. The augmented fifth is a little larger.

Main article: diminished fifth
Main articles: tritone, minor sixth

Pitch ratio

The pitch ratio of a perfect fifth is 3:2. This means the higher note shakes three times while the lower note shakes two times. When a violin is tuned this way, it sounds smooth.

Keyboard instruments like the piano often use a changed version of the perfect fifth. This helps the piano play in all keys. This changed perfect fifth is a little smaller than the exact 3:2 ratio.

Use in harmony

The perfect fifth is important for making chords in music. It helps create major and minor triads, which are used in many songs. Instruments naturally make perfect fifths, so musicians sometimes skip the fifth note of a chord.

The perfect fifth is also in more complex chords, like seventh chords, where it can make harsh sounds softer. In modern music, stacking perfect fifths makes quintal harmonies. Composers like Paul Hindemith and Stravinsky have used this.

Bare fifth, open fifth, or empty fifth

A bare fifth, open fifth, or empty fifth is a chord that has only a perfect fifth note, without a third note. This type of chord ends some famous pieces, like those by Pérotin and Guillaume de Machaut. It also appears in the Kyrie of Mozart's Requiem and the first movement of Bruckner's Ninth Symphony. You can find these chords in Medieval music, Sacred Harp singing, and many kinds of rock music.

In styles like hard rock, metal, and punk music, musicians use bare fifths because they sound clear on overdriven or distorted electric guitar. These chords, called power chords, are easy to play fast. Empty fifths are also used in traditional music, such as in Asian and some Andean music styles. Composers use these chords to make a special or mysterious sound.

Use in tuning and tonal systems

The perfect fifth, along with the octave, is important in Pythagorean tuning. A slightly smaller perfect fifth is also used in meantone tuning.

The circle of fifths helps us see how notes relate to each other in music. It shows how many perfect fifths are needed to move from one note to another in the chromatic scale.