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Third (Interval) – Definition
A third is a musical interval spanning three letter names. It is one of the most important intervals in Western music because it determines whether a chord sounds major or minor.
What is a Third?
There are two main types of thirds: the major third, consisting of four semitones, and the minor third, consisting of three semitones. In a basic triad, the third is the note positioned above the root and is responsible for the chord’s major or minor quality.
Because of its harmonic importance, the third plays a central role in chord construction, harmony, and melody.
Why is the Third important for pianists?
Understanding thirds allows pianists to build chords quickly and recognize whether a chord is major or minor. It also improves harmonization, ear training, and improvisation.
Whether playing from chord symbols or arranging melodies, recognizing the correct third is essential for creating the intended harmonic color.