|175x175px The major third may be derived from the
harmonic series as the interval between the fourth and fifth harmonics. The
major scale is so named because of the presence of this interval between its
tonic and
mediant (1st and 3rd)
scale degrees. The
major chord also takes its name from the presence of this interval built on the chord's
root (provided that the interval of a
perfect fifth from the root is also present). A major third is slightly different in different
musical tunings: In
just intonation it corresponds to a pitch ratio of 5:4, or () (fifth harmonic in relation to the fourth) or 386.31
cents; in
12 tone equal temperament, a major third is equal to four
semitones, a ratio of 21/3:1 (about 1.2599) or 400 cents, 13.69
cents wider than the 5:4 ratio. The older concept of a "
ditone" (two 9:8 major seconds) made a dissonant, wide major third with the ratio 81:64 (about 1.2656) or 408 cents (), about
22 cents sharp from the harmonic ratio of 5:4 . The
septimal major third is 9:7 (435 cents), the
undecimal major third is 14:11 (418 cents), and the
tridecimal major third is 13:10 (452 cents). In 12 tone equal temperament three major thirds in a row are equal to an octave. For example, A to C, C to E, and E to G (in the differently written notes G and A both represent the same pitch, but
not in most other
tuning systems). This is sometimes called the "
circle of thirds". In just intonation, however, three 5:4 major third, the 125th
subharmonic, is less than an octave. For example, three 5:4 major thirds from C is B (C to E, to G, to B) ( = \tfrac{\; 5^3 \ }{\; 2^6\ } = \tfrac{\ 125\ }{ 64 }\ ). The difference between this just-tuned B and C, like the interval between G and A, is called the "enharmonic
diesis", about 41 cents, or about two
commas (the
inversion of the interval : \ \frac{\ 128\ }{ 125 } = \frac{\; 2^7\ }{\; 5^3 }\ ()). == Consonance vs. dissonance ==