9.1 The classification of intervals
a) An interval is described as:
- harmonic when its component pitches are played simultaneously;
- melodic when its component pitches are played successively;
b) Intervals are described as:
- simple if they are within the range of an octave:
- compound if they are larger than an octave.
Compound intervals can be reduced to simple intervals and classified in the same way.
For example, the compound interval Major 10th may be reduced to the simple interval Major 3rd. Both are major.
| Major 10th | Major 3rd |
Braille example
c) In the classical music tradition intervals are classified as:
Consonant:
- major and minor 3rds,
- perfect 4ths,
- perfect 5ths,
- major and minor 6ths,
- perfect octaves
Dissonant
- 2nds
- 7ths
- all the augmented and diminished intervals.
d) Interval may be:
Diatonic: when both the pitches in the interval are part of the same tonality,
Chromatic: when one of the pitches is not a part of the tonality.
Esempio nella tonalità di re maggiore:
| diatonic interval | chromatic interval | chromatic interval | diatonic interval |
Braille example
9.2 Inversions
An interval is said to be inverted when the lower note is raised by an octave to become the higher note.
For example the inversion of the Major 3rd C-E is the Minor 6th E-C:
| Major 3rd | Minor 6th | Major 3rd | Minor 6th |
Braille example
The sum of any interval and its inversion will always be 9 - for example the 3rd plus the 6th:
- As you can see from the example the inversion of a major interval will be a minor interval and vice versa.
- The inversion of a diminished interval will be an augmented interval and vice versa. The inversion of a doubly diminished interval will be a doubly augmented interval and vice versa.
- Perfect intervals remain perfect when they are inverted.
9.3 How to recognise an interval.
In classifying the type of interval it is useful to refer to keys.
Think of the lower not of the interval as the tonic of a major scale we can make the following observations:
a) if the upper note is part of the same scale it will be:
- major if it is a 2nd, 3rd, 6th or 7th
- perfect if it is a 4th, 5th or octave.
b) if the upper note is raised by a semitone with respect to the scale then the interval will be:
- augmented
- doubly augmented if it is raised by two semitones
c) if the upper note is lowered by a semitone with respect to the scale then the interval will be:
- minor if the interval is a 2nd, 3rd, 6th or 7th
- diminished if it is a 4th, 5th or octave.
d) if the upper note is lowered by 2 semitones with respect to the scale then the interval will be:
- diminished if the interval is a 2nd, 3rd, 6th or 7th
- doubly diminished if it is a 4th, 5th or octave.
From this we can say that:
A major interval:
- enlarged by a semitone becomes augmented,
- enlarged by 2 semitones becomes doubly augmented,
- diminished by a semitone becomes minor
- diminished by 2 semitones becomes diminished
- diminished by 3 semitones becomes doubly diminished
A perfect interval:
- enlarged by a semitone becomes augmented,
- enlarged by 2 semitones becomes doubly augmented,
- diminished by a semitone becomes diminished
- diminished by 2 semitones becomes doubly diminished
The intervals in the example below are described as follows:
- C-C is a unison
- C-C# is an augmented unison
- C-C flat is a diminished unison
| unison | augmented unison | diminished unison |
Braille example
The classification of the intervals can also be related to the major and minor scales.
Almost all of the intervals that can be major or minor – 3rds, 6ths and 7ths are minor in minor scales. The exception is the 2nd which is major in both major and minor scales.
The intervals of unison, 4th, 5th and octave are perfect in both major and minor scales.
In conclusion, here is a series of examples of intervals and a brief guide to help with their recognition.
a) C – E flat = interval of a 3rd
If the interval were C to E natural then, because E natural is the third note of the C major scale, the interval is major.
When a major interval is lowered by a semitone it becomes minor. C to E flat is a minor 3rd.
b) B – G flat = interval of a 6th.
G flat is not part of the B major scale but is two semitones lower than the G# that is the 6th degree of the B major scale. Therefore this interval is diminished.
c) G# - D flat = interval of a 5th.
The key of G# major is not used therefore let us change the interval temporarily to G-D flat. D would not be flat in the G major scale and so G-D flat would be a diminished 5th. The interval is, in fact, made even smaller by the sharpening of the G making this interval a doubly diminished 5th.