It was the English composer John Dunstable who introduced the third to music, creating the unique color palette that allowed Western music to flourish. In short, a “third” is simply the third note above the root note: If your root note is a C, the third interval is an E. Thirds are referred to in music as imperfect because they can be both major and minor (depending on where you start). And, of course, when you stack two thirds together, you get the 1-3-5 triad—the foundation of all Western music through to that pop tune that came out last week.
Dunstable also found that there was an inherent logic that knitted together different triads, since each triad is composed of two notes of a different triad. Moving from one closely related triad to another gives a logic to music that has informed our understanding of harmony to this day. This video gives a great introduction to triads and chord theory:
Don’t worry about diminished and augmented chords, as they won’t become really relevant for a few hundred years.
Of Dunstable’s other major developments, his revolutionary decision to move the melody from the tenor line to the top treble line is the most significant. In this, he broke the continental preference for dissonance and the primacy of lower voices. Before Dunstable, music was, with very few exceptions, dull, sparse and predictable. Dunstable is responsible for bringing the color of the Renaissance to music and with his music that we start our musical journey in earnest.
John Dunstable, Quam Pulchra Es:
Several hundred years later, a retired miner in the north of England composed a song based on a traditional Yorkshire ballad. Drawing his musical inspiration from the Middle English period (roughly from the 5th to 16th centuries), Ewan MacColl’s remarkable 1947 Canticle has been performed by many bands over the years, including most memorably by Simon and Garfunkel. From their legendary concert in Central Park, when these two brilliant musicians transported 1980s New York back to the English Renaissance, if just for a few minutes.
Simon and Garfunkel, Scarborough Fair:
Incidentally, I should note that my personal Rosetta Stone for Early Music was the Kronos Quartet’s remarkable album “Early Music” from the late 1990s. Kronos was, and remains, on the vanguard of contemporary music, but this album saw the group reach back across the centuries to find the inspiration for much of what they had been performing. The album effectively presents contemporary music along side music written several hundred years ago. The effect, for me, was remarkable and I recommend the album highly. It is one of my Desert Island Discs.
A Gertus History of Music 