Musica ficta (Latin for "false music") is the primarily Medieval act of unscripted chromatic alterations of notes in written music by a performer in order to avoid unpleasant tonal harmonies.

First, a bit of music theory primer. A chromatic alteration is a note one semitone up or down from another. Thus, C# is the chromatic step up from C, and Gb is the chromatic step down from G. Secondly, while there are of course many accepted tonal conventions such as the major triad and minor seventh, there also a number of tonal combinations which are very harsh and dissonant to the ear. Of course in the 21st century a number of compositions have made their fame on being deliberately atonal and dissonant, but in the Medieval and Renaissance periods, dissonance was a vice, not a virtue, and as such tones which produced it were avoided at all costs.

Without getting bogged down into too much theory, the standard octave scale consists of 12 tones. In the octave beginning with C, for example, the tones are C-C#-D-D#-E-F-F#-G-G#-A-A#-B-C (this last C is actually the first tone of the next octave.) The chief clashing tone of the major scale is known as the tritone, called such because it contains three equidistant tones within the scale, each 6 semitones (i.e. chromatic steps) above the other. In the C octave again, that would be C, F#, and C. In Medieval texts this is referred to as "diabolus in musica" - literally, "The devil in the music." And if you know your history, you know that when Medieval people invoked the devil, they meant serious business.

The introduction of musica ficta came around the 13th century in large part to the introduction of the flat seventh to the common repertoire of major music. The flat seventh is a bit of a musical wunderkind during this period, as it fulfills a lot of music theory's quirky needs:

  • It provides surprise without being dissonant;
  • It provides harmony with all three major chord bases within the major scale (the first, fourth, and fifth notes);
  • and, most importantly, it allows the fourth note to avoid the tritone. Typically, the fourth would be paired with the first note, but given the first note's dominance over the entire piece (since the piece was written in the key of the first note), this could be repetitive and boring. But the alternative was to pair the fourth with the seventh - a tritone! The flat seventh avoids the tritone, and even more, provides the fourth with its own fourth. Very versatile, that flat seventh is.

So because the flat seventh is coming into popularity, musica ficta takes hold. That is, performers began taking old pieces which paired the fourth and the seventh, and more or less making a mental note to sing the flat seventh instead of the seventh. Purists balked; a mockery of the music provided, they said. Conservatives demurred; maybe this musica ficta was good enough for choral pieces, but plainchant was simply off-limits for this kind of frivolity. Theorists argued over its placement.

And, as with all things theoretical, people began applying the concept of musica ficta to other tones, not just the fourth/seventh combo. It's really like the first version of improvisation (although jazz theorists will surely argue that improvising tones to avoid dissonance kind of misses the point.) This caught on so much that composers began indicating potential tonal choices as accidentals (notes which are not found in the key a piece is written in) by the 14th century, a practice still in use today.

Today, of course, there are truly universal rules of polyphony, and it is accepted in its many variations. Romanticism, Modernism, jazz, and rock n' roll have legitimated virtually all forms of music, however tonal or dissonant it may be. But the concept of musica ficta lives on with every composer and performer, with every note they choose to write and play.