An interval in music is simply "The distance between two notes" (or tones). Intervals are formed by using the notes in the Major/minor scales. A diminished interval is a Perfect or Major/Minor interval that has been made smaller by one half-step.
Each interval has 2 names: One of those names is a number, which is usually between 1 and 13, and the other name is the type of interval.
An interval can be:
Perfect intervals are found in both Major and minor scales: 1 (unison), 4, 5, 8 (octave)
Major Intervals are found in only the Major scale: 2, 3, 6, 7
Minor intervals are found only in the minor scale: 2, 3, 6, 7
Perfect Intervals can never be Major or Minor intervals.
Major or Minor intervals can never be Perfect Intervals.
An augmented interval is a Perfect or Major/Minor interval that has been made larger by one half-step.
NUMBER Perfect or Augmented or
OF
HALF
STEPS
Major or
Minor
Diminished
0
Perfect Unison
Diminished 2nd
1
Minor 2nd
Augmented unison
2
Major 2nd
Diminished 3rd
3
Minor 3rd
Augmented 2nd
4
Major 3rd
Diminished 4th
5
Perfect 4th
Augmented 3rd
6
Tritone
Augmented 4th
Diminished 5th
7
Perfect 5th
Diminished 6th
8
Minor 6th
Augmented 5th
9
Major 6th
Diminished 7th
10
Minor 7th
Augmented 6th
11
Major 7th
Diminished 8th
12
Perfect 8
Augmented 7th