Picardy Third

A Picardy third (also known as Tierce de Picardie) is a harmonic device used in European classical music.

It refers to the use of a major chord of the tonic at the end of a musical section which is either modal or in a minor key. This is achieved by raising the third of the expected minor triad by a semitone to create a major triad, as a form of resolution.

For example, instead of a cadence ending on an A minor chord containing the notes A, C, and E, a tierce de Picardie ending would consist of an A major chord containing the notes A, C#, and E. Note that the minor third between the A and C of the A minor chord has become a major third in the tierce de Picardie chord.

Even in instrumental music, the picardy third retains its expressive quality: it is the “happy third.”…Since at least the beginning of the seventeenth century, it is no longer enough to describe it as a resolution to the more consonant triad; it is a resolution to the happier triad as well.…The picardy third is absolute music's happy ending. Furthermore, I hypothesize that in gaining this expressive property of happiness or contentment, the picardy third augmented its power as the perfect, most stable cadential chord, being both the most emotionally consonant chord, so to speak, as well as the most musically consonant.

The Picardy third does not necessarily occur at the end of a section: it can be found at any perfect cadence or plagal cadence where the prevailing key is minor.