A family of tuning systems that can have fewer than twelve12 tones per octave or many more than twelve12. Just intonation is based on any pure, natural scale determined by the frequencies of the harmonic series of the tonic, not one that is artificially fixed by keyboard instruments. Purely tuned just intervals are almost never used in music because of their incompatibility with the octave. Scales in just intonation are never equal tempered, and vice-versa. See syntonic comma, diatonic comma, and temperament.