It refers to the use of a major chord of the tonic at the end of a musical section that 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.
What makes this cadence a tierce de Picardie is shown by the red natural sign – instead of the expected B flat (which would make the chord minor) the accidental gives us a B natural, making the chord major.
Other examples include the last chord in the first movement of Bach's Concerto for Two Violins in D minor, the final chord of Bach's 'Little' Fugue in G minor for organ,, final cadence of Bach's fuga from the second solo violin sonata in a minor, and the final chord in Gregorio Allegri's Miserere Mei, Deus. The Bach examples are good illustrations of the "stable" character of a Picardy third, while the Miserere Mei can easily be interpreted as "bittersweet".
Thomas Bateson's 15th century madrigal 'Your Shining Eyes' features use of the Picardy third in bar 16. A more modern example is found in The Beatles' And I Love Her, which closes on a D major chord from a final passage in the key of F major/D minor. Other modern examples include "Roundabout" by the band Yes, "Sweet Child o' Mine by Guns N' Roses, and the Black Sabbath classic "N.I.B." where the final guitar riff over an E power chord ultimately slides down to and sustains G♯.
The origins of the term are obscure. An idea that was repeated as fact for some time, but turns out to have no provable basis, was that expounded by Jean-Jacques Rousseau in his Dictionnaire de Musique (1767): that this form of ending survived longest in church music, and due to the great number of cathedrals in the historical French province of Picardy. More plausible is the idea that the North of France, and Flanders, were influential in the development of contrapuntal music in the fifteenth century.
Robert Hall hypothesizes that, instead of deriving from the Picardy region of France, it comes from the Old French word "picart," meaning "pointed" or "sharp" in northern dialects, and thus refers to the musical sharp that transforms the minor third of the chord into a major third. In medieval music, such as that of Machaut, neither major nor minor thirds were considered stable intervals, and so cadences were typically on open fifths. Examples of the Picardy third can be found throughout the works of J.S. Bach and his contemporaries, as well as earlier composers such as Thoinot Arbeau and John Blow.
This practice began to decline in the late sixteenth century and by the Classical era had been more or less discarded, although examples can be found in works by Haydn and Mozart. In the Romantic era, those of Chopin's nocturnes that are in a minor key almost always end with a Picardy third. A notable structural employment of this device occurs with the Finale of the Tchaikovsky Fifth Symphony, where the motto theme makes its first appearance in the major mode.
It is notable that in the first book of J. S. Bach's The well-tempered clavier composed in 1722, only one of the twenty-four minor movements fails to end in a Picardy third, whereas in the second book, composed in 1744, fourteen end without it. (Manuscripts vary in some of these cases. This is the case with the single exception in the first book, the G♯-minor fugue, which, according to the present Bach Gesellschaft edition, is thought to have been originally composed in G minor, accounting for the natural sign rather than sharp on the third of the final chord.)
When a composer has not directly indicated a major or minor chord, it is occasionally acceptable to add Picardy thirds to a work in the interests of variety, especially in earlier music. This is usually decided by the continuo players in a chamber work. For example, in performances of the Rosary Violin Sonatas by Heinrich Ignaz Biber, many continuo players add variety to the frequent repetitions in movements consisting of variations by adding the occasional Picardy third. However, over-indulgence of this liberty could weaken the work's structure.
Related chords 
A similar effect, often used, is created with a deceptive cadence leading to the flattened sixth (for example, in C major, replacing the expected tonic chord with A flat major); this effect utilizes the lowered third but without affirming the tonic key.
Popular music / Notable examples 
- Beethoven - Hammerklavier, slow movement
- The Beatles - "And I Love Her", last measure (mentioned in Everett's book The Beatles as Musicians[full citation needed])
- Bob Dylan - "Ain't Talkin'", the final song on Modern Times (2006), is played in E minor but ends (and ends the album) with a ringing E major chord
See also 
- Bruce Benward and Marilyn Nadine Saker (2009). Music in Theory and Practice: Volume II, eighth edition (Boston: McGraw-Hill), p. 74. ISBN 978-0-07-310188-0.
- Percy Scholes (ed.) (1955). The Oxford Companion to Music: Self-indexed and with a Pronouncing Glossary and Over 1,100 Portraits and Pictures, ninth edition, completely revised and reset and with many additions to text and illustrations (London and New York: Oxford University Press), pp. 1027–28.
- Peter Kivy (1999). Osmin's Rage: Philosophical Reflections on Opera, Drama, and Text, with a New Final Chapter (Ithaca and London: Cornell University Press), p. 289. ISBN 978-0-8014-8589-3.
- Denise LaGiglia and Anna Belle O'Shea (2005). The Liturgical Flutist: A Method Book and More (Chicago, IL: GIA Publications), p. 166. ISBN 978-1-57999-529-4.
- Robert A. Hall, Jr. (1975), "How Picard was the Picardy Third?", Current Musicology 19: pp. 78-80.
- Robert S. Hatten (1994). Musical Meaning in Beethoven: Markedness, Correlation, and Interpretation (Bloomington: Indiana University Press), p.39. ISBN 0-253-32742-3. First paperback reprint edition 2004. ISBN 978-0-253-21711-0.
- See Ain't Talkin in Songs list at dylanchords.info. The guitar part is played in Em with a capo on the 4th fret, so the song sounds in the key of G♯ minor.
Further reading 
- Ruff, Lillian M. 1972. "Josquin Des Pres: Some Features of His Motets". The Consort: Annual Journal of the Dolmetsch Foundation 28:106–18.