Intervals

An interval is the separation between two notes.

The smallest interval in western harmony is a called a semitone. That is the interval between two adjacent keys on a piano, or two adjacent frets on a guitar. Other intervals can be measured in the number of semitones that they contain.

Intervals are mostly identified by ordinal numbers, like 2nd, 3rd and 4th. In the key of C, these numbers correspond to the position of the white notes on a piano keyboard, relative to the root note C.

The black notes are often described relative to white note above it.

Intervals in the first octave

Here is a list of the intervals in the first octave.

The names of the intervals make most sense when we look at them on the piano keyboard in the key of C.

Here you can see, that:

• the 1st white key is the root
• the 2nd white key is the 2nd
• the 3rd white key is the 3rd
• the 4th white key is the 4th
• and so on

In the case of the 2nd, 3rd, 6th and 7th, there is a major and a minor version, where:

• the major version is the white key and
• the minor version is the black key below it.

This pattern is broken for the 4th and 5th notes, which are refered to as perfect 4th and perfect 5th.

Relative to the 5th, we can also talk about:

• a diminished 5th, which is the same as the tritone
• an augmented 5th, which is the same as a minor 6th

Intervals in the second octave

You can continue the same logic into the second octave.

Again, it helps to relate the intervals to the white notes on the piano keyboard in the key of C.

As before, you can see that:

• the 9th white key is the 9th
• the 10th white key is the 10th
• and so on

Note:
Although we have included a minor 14th and major 14th in the list, these names are never really used.

Intervals in chords

With regard to chords, we use intervals in two ways:

• the separation between notes in a chord
• the position of a note relative to the root note

The separation between notes

One way to build chords, is by stacking intervals.

For example a C major triad is build from a major third followed by a minor third.

Looked at on the piano keyboard, we can see that:

• the interval between C and E is 4 semitones
• the interval between E and G is three semitones

We can see exactly the same on a guitar fretboard:

• the interval between C and E is 4 frets
• the interval between E and G is 3 frets

The position of a note relative to the root note

It is very often useful to refer to the position of a note within a chord, relative to the root of the chord.

In the C major triad, the root note is C.

The note E is a major 3rd above the C. In the chord, we call this note the major 3rd, or simply the 3rd.

The note G is a perfect 5th above the C. In the chord, we call this note the fifth.

Sometimes, using a convention known as Roman numeral analysis the levels are described using roman numerals.

When we add additional notes to a chord, for example the 6th, 7th or 9th, we always refer to the notes by their position relative to the root note.