A perfect fifth is an interval of seven semitones (half steps) between 2 notes. For example, if you play a C on the piano followed by the G above it then you will have just played an example of a perfect fifth:
The G is 7 semitones higher than the C and so the interval is described as a perfect 5th.
You can do the same starting on any note.
For example, if you find an F sharp on the piano… count up 7 semitones and you will reach a C sharp.
The interval between the F sharp and the C sharp above it is a perfect fifth:
You can repeat this process of counting up 7 semitones starting on any note of the chromatic scale as shown in this table:
When describing an interval of a fifth the letter names of the notes must always be 5 apart (e.g. C – G is 5 letter names – C, D, E, F, G).
For example, the distance between F# and Db is 7 semitones, but it is not a perfect 5th as “F” and “D” are 6 letter spaces apart (F, G, A, B, C, D) – the correct description of the perfect 5th would be F#-C# or Gb-Db depending on the context of the music.
Why is it called a Perfect Fifth?
The term “perfect” is used to describe the following intervals:
This dates back to medieval times where these intervals were thought of as the most “consonant” and so were named perfect.
The perfect 5th and the perfect 4th are closely related in terms of harmony as the inversion of a perfect 5th is a perfect 4th – e.g. if you invert the interval C-G it becomes G-C (perfect 4th)
The perfect fifth is also the main interval in the construction of major and minor triads.
Not surprisingly, there are numerous examples of perfect fifths being used by composers for centuries.
In medieval times, composers often used the interval as the basis for techniques such as parallel organum or for drones. The interval works very well for drones in folk music as the absence of any 3rd (major or minor) doesn’t “colour” the sound and can be used to accompany a wide variety of melodies.
It is really helpful to listen to an interval in the context of a piece of music so that you can train your ear to recognise it. Two very famous examples of perfect fifths that will help you to do this are Twinkle Twinkle Little Star and “The Last Post”.
In Twinkle Twinkle Little Star, the first “Twinkle” sounds on the root note and then the second “Twinkle” sounds a perfect fifth above it.
In “The Last Post” (a solo trumpet/bugle piece played at military funerals and remembrance events in the United Kingdom and the Commonwealth), the first two notes of the melody form the interval of a perfect 5th.
This very famous opening is deeply moving and poignant. Have a listen to this example of The Last Post played by a member of the Royal Military College band. You can hear clearly the emotive impact of the opening interval in the melody.
Open Fifths (otherwise known as Bare fifths or empty fifths) are when a chord is played containing a root note and a fifth, but with no third.
The sound produced has a characteristic open/bare/empty feel to it (hence the names!).
These have been popular with composers for some time.
Composers would often use them to conclude a piece of music. For example, the last chord of the Kyrie from Mozart’s Requiem is an open fifth.
In contemporary music the power chord in rock music is built on the concept of an open fifth.
The empty/bare sound of the harmony (often with the addition of a doubled octave as well) means that it can be strummed repeatedly without creating a “muddy” sound. You can hear from this example below how the openness of the sound enables the repeated “driving” sound to be created:
The power chord is no longer a technique that is exclusive to rock music as it has spread across different genres and instruments. You will often hear open fifths used in dance music played on synth parts to give increased energy to a track.
It is worth listening to the above examples repeatedly so that you begin to recognise the characteristic sound of the interval. It is also worth experimenting with it in your composition work as the more you use the interval the more you will start to understand when and where it can be most effective.