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Intervals are the fundamental building blocks of music allowing us to read and write music, and most importantly, to help us construct chords and harmonies. However words like major, minor, augmented, diminished, enharmonic and compound leave many people a bit confused, hopefully this article will throw some light on the subject.

The 'distance' between two notes is known as an interval. This is the difference in pitch between two notes. The size or amount of distance is measured numerically.

If we consider the C scale there are 8 notes; C D E F G A B C numbered from 1 through to 8. As an example the interval from C to G is a 5th as G is 5 notes above C. The interval from C to F is a 4th as F is 4 notes above C.

All intervals are measured from the first note of the scale. These intervals are given a name as well as a numeric value and in order of progression they are: C-D is a major 2nd, C-E is a major 3rd, C-F is a perfect 4th, C-G is a perfect 5th, C-A major 6th, C-B major 7 and finally C-C is a perfect octave.

The intervals that are perfect are so called because they have a certain purity about them that comes from the overtones and upper-partials that are contained within them (these will be explained in another article)

Intervals can be raised or lowered by a half-step/semitone. If a major interval is chromatically reduced by a half-step it becomes a minor interval e.g. C-E is a major 3rd, if it is lowered by a half-step (from C-Eb) the interval becomes a minor 3rd.

If a perfect interval is chromatically reduced by a half-step it becomes a diminished interval i.e. a perfect 4th lowered by a half-step becomes a diminished 4th.

If major or perfect intervals are raised by a half-step then they become an augmented interval i.e. a perfect 5th would become an augmented 5th.

Compound intervals are those that extend into the 2nd octave. C to D (in the next octave) is called either a major 9th or a compound major 2nd. C to F (next octave) is a perfect 11th or a compound perfect 4th.

Enharmonic intervals are those that differ in name but not pitch, for example C-G# is an augmented 5th and C-Ab is a minor 6th.

When intervals are inverted they reverse the relative position of the notes. C-G (perfect 5th) becomes G-C which is a perfect 4th, a 3rd would become a 6th. Perfect intervals when inverted remain perfect e.g. C-G being a perfect 5th would become a perfect 4th when inverted, a major becomes minor, minor becomes major, diminished becomes augmented and augmented becomes diminished.

These rules apply to all scales.