Chapter 3 · Lesson 02

Interval Qualities

⏱5 min read

In the previous lesson we learned to find the size of an interval, its number. But two intervals of the same size may not be exactly equal. That is where the interval's second characteristic comes in, its quality.

01Same size, different sound

Compare two seconds: from C to D, and from E to F. Both are seconds, two neighbouring note names. But they are not equal. C-D spans a tone, while E-F spans only a semitone.

Two seconds that are not equal
C-D · tone
major second (M2)
E-F · semitone
minor second (m2)
Two seconds with a different sound. C-D spans a tone, so it is major (M2). E-F spans a semitone, so it is minor (m2).

02The five qualities

There are five interval qualities, each with its own abbreviation: minor (m), major (M), perfect (P), augmented (A) and diminished (d).

Each size, though, takes only certain qualities. Seconds, thirds, sixths and sevenths are minor or major, one semitone apart. Unisons, fourths, fifths and octaves don't split into minor and major. They have only one natural form, which is why they are called perfect.

03How many tones each one spans

The table below shows every quality with its tones and an example, all starting from C. Notice the pattern: the minor interval is always one semitone below the major one.

The intervals and their tones
IntervalAbbr.TonesExample from C
minor 2ndm2½C-D♭
major 2ndM21C-D
minor 3rdm31½C-E♭
major 3rdM32C-E
perfect 4thP42½C-F
perfect 5thP53½C-G
minor 6thm64C-A♭
major 6thM64½C-A
minor 7thm75C-B♭
major 7thM75½C-B
perfect octaveP86C-C
All the interval qualities up to the octave, with the tones each one spans and an example starting from C.

04Augmented and diminished

The last two qualities describe intervals that are slightly larger or slightly smaller than usual. When a perfect or major interval grows by one semitone, it is called augmented (A). When a perfect or minor interval shrinks by one semitone, it is called diminished (d). This applies to an interval of any size, and it can come from accidentals or even from natural notes.

Augmented and diminished from C
C-F♯ · 3 tones
augmented 4th (A4)
C-G♭ · 3 tones
diminished 5th (d5)
The perfect 4th (C-F, 2½ tones) with a sharp becomes augmented (C-F♯, 3 tones). The perfect 5th (C-G, 3½ tones) with a flat becomes diminished (C-G♭, 3 tones).

05Enharmonic intervals

Look again at the two intervals in the figure above. C-F♯ (A4) and C-G♭ (d5) both span 3 tones, so they sound identical. But they are written differently and have different names. Two intervals with the same sound but different spelling are called enharmonic.

Recap

  • The quality says exactly how large an interval is: minor (m), major (M), perfect (P), augmented (A), diminished (d).
  • Seconds, thirds, sixths and sevenths are minor or major. Unisons, fourths, fifths and octaves are perfect.
  • The difference between minor and major is one semitone.
  • Perfect or major + semitone = augmented. Perfect or minor − semitone = diminished.
  • Example from C: C-F♯ = augmented 4th, C-G♭ = diminished 5th.
  • Two intervals with the same sound but different spelling are called enharmonic (C-F♯ and C-G♭).

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