The Perfect Fifth: The Basis of All Harmony? | Hub Guitar

The Perfect Fifth: The Basis of All Harmony?

After you’ve been studying music theory, one thing that you’ll start noticing is that the perfect fifth seems to be a recurring theme. This interval is the most consonant of all intervals which can be formed from a different note other than the root. Many people believe this interval is the basis of harmony.


It is not only the modern musical system that is based on the perfect fifth, but many, if not most or all, primitive musical systems.

All Notes Come From the Fifth

Pythagorean TuningOne of the earliest 12-note tuning systems, based on a series of perfect fifths which establishes the 12-note scale of modern music: C, G, D, A, E, B, F♯, C♯, G♯, D♯, A♯, F. , one of the earliest (if not the earliest) 12-note tuning systems, was conceived of by imagining a series of perfect fifths from C: G, D, A, E, B, F♯, C♯, G♯, D♯, A♯, F. However, the perfect fifth we hear when we are tuning corresponds to a ratio of 3:2, which equals a difference of 702 centA cent is a unit measuring the difference in pitch between notes. In most cases, two notes are separated by exactly 100 cents, which means there is 1200 cents in an octave. If a note is more than 5 cents out of tune, the difference starts to become noticeable.s. So tuning to the 12 chromatic notes from this knowledge proved difficult as the sum of 12 of these perfect fifths is 8424 cents. Since an octave is 1200 cents, when we arrive back at C, it should be 7 octaves above or 8400 cents. If we use our ear to tune up in a series of fifths, upon arrival back at “C”, this note would be audibly out of tune with the original C.

That’s where equal temperament comes in to play. Equal temperament attempts to compensate for this by slightly correcting the tuning of each note. This means they will all be slightly “off” or out of tune when compared as perfect fifths, but the amount is only very slight—and, in the end, the final “C” matches perfectly with the original C.

So under equal temperament, the fifth is very slightly corrected from 702 cents to 700 cents. This difference is not really noticeable, and now all notes can be tuned to consistent and equal pitches.

The Perfect Fifth in 12-TET

The perfect fifth is represented almost completely accurately in 12-tone equal temperament, suggesting that its accuracy is fundamental to music.

The Root Note of the Nearest Key

In any given key, the closest tonalityThe key in which a piece is played, and the relationships of the notes to each other, and most especially to the tonal center. is the key of the 5th or 4th degrees. (Since the fourth is an inversion of the fifth, it is also a fifth, but backwards). This means that in the key of C major, the closest key up is G major, because G has only one note different than C.

Strong Presence in the Harmonic Series

For any given note, a series of overtoneIn the harmonic series, an overtone is any note other than the fundamental. Overtones add subtle coloring to every note, but most of them are not audible by themselves.s can be heard. This is called the harmonic seriesThe harmonic series is an array of pitches produced whenever any note is played on any acoustic instrument. This array of pitches is a natural consequence of acoustic physics. . In the harmonic series, the strongest overtones are on the bottom. The first and strongest overtone (excluding the root and octaves) is the perfect fifth. This means that whenever you play any note, the note a perfect fifth above is also audible in the overtones of the first note. So if you play a “C” note, you’re also playing a “G” note.

Because of this strong relationship between a root and its fifth, the overtones of each note will also match closely. In other words, they imply very strongly related or consonantA note that is consonant with another will seem to agree and fit well when played together with the first. harmonies with respect to each other.

Tuning Instruments

Many instruments are tuned in fifths or fourths, including the guitar.

Traditional Harmony

In traditional counterpoint, use of the fifth as a harmony is usually not allowable because the fifth isn’t a harmony as it’s too consonant with the root.

Easy to Hear

The fifth is one of the easiest intervals for humans to learn to sing, meaning it is a strong and easily-learned musical interval that most people can learn to hear relatively quickly.

Almost all chords have an unaltered (perfect) fifth above the root.

Theories of Organizing Tones

George Russell’s Lydian Chromatic Concept of Tonal Organization is based on the perfect fifth as well. This system posits that all harmony is based on fifths and that the Lydian mode is the ideal structure. The Lydian mode can be created from a series of perfect fifths: C–G–D–A–E–B–F♯. Re-arrange them and they form the Lydian scale. Of course, the major scale is fairly close, too: start this sequence on “F” and you’ll end up with a C major scale if you keep C as the tonal center.

Key Points

As the creator of Hub Guitar, Grey has compiled hundreds of guitar lessons, written several books, and filmed hundreds of video lessons. He teaches private lessons in his Boston studio, as well as via video chat through TakeLessons.

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