Pertaining to the interval of a 3rd (or third), whether major, minor, or neutral. Generally refers to common-practice harmony, in which chords are built in 3rds.
The traditional harmonic system of Western European music is limited to ratios of prime numbers no higher than 5. The primes 2, 3 and 5 define the Major [Thirds] and Minor Thirds [with the ratios] 5/4 and 6/5 and their compounds, and name is derived from the Latin word for third, tertius.
By an accident of language, tunings limited by the prime number 5 are termed "Tertian, " while those bounded by the prime number 3 are called "Quintal," or "Quartal."
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