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Definition: A third is an interval equal to three scale degrees that is most often major or minor*:
  • Major Third (M3)
    Equal to four half steps; the distance between GB is a major third.

  • Minor Third (m3)
    Equal to three half steps; GB
* (By itself, “third” can refer to a major third – it’s common to omit the word ‘major’ when speaking of intervals, chords, and keys.)

The Third as a Scale Degree

The third note or chord in a musical scale. When reading or playing a scale, the third note will be the first clue as to whether that scale is major or minor. Compare the following G scales:
  • G Major:  G - A - B - C - D - E - F♯
  • G Minor:  G - A - B♭ - C - D - E♭ - F

 ►  View G Major’s Key Signature
 ►  View G Minor’s Key Signature

The Role of the Third in Chords

In many chord types, the third is an important building block. For example, major and minor chords are built similarly, except for their thirds: See root note.

Also Known As:
  • terza [maggiore / minore]  (It)
  • tierce [majeure / mineure]  (Fr)
  • Terz [grosse Terz / kleine Terz]  (Ger)

More Musical Intervals:

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