Just intonation is a tuning system that tunes musical intervals using simple whole-number frequency ratios. In Western music, it represents an approach that prioritizes acoustic purity and consonance over flexibility across keys.
Just intonation has played an important role in the development of Western harmony, even though it is not the dominant system in modern practice.
What Is Just Intonation?
In just intonation, pitches are tuned so that intervals align closely with ratios found in the harmonic series. These ratios produce intervals that sound particularly stable and consonant to the ear.
For example, a perfect fifth tuned in just intonation follows a 3:2 frequency ratio, while a major third follows a 5:4 ratio.
Just Intonation and the Harmonic Series
The logic of just intonation comes directly from the harmonic series. When two pitches share simple frequency relationships, their overtones align more closely, reducing acoustic tension.
This alignment is why justly tuned intervals often sound smooth and resonant compared to their equal-tempered equivalents.
Just Intonation and Musical Keys
Just intonation works best within a single key. Intervals are tuned relative to a specific tonal center, allowing chords in that key to sound especially pure.
However, when music modulates to another key, the same pitches no longer maintain simple frequency ratios. Notes that sounded consonant in one key can become noticeably out of tune in another.
Limitations of Just Intonation
Because just intonation depends on key-specific tuning, it is difficult to apply consistently across all keys without retuning. Fixed-pitch instruments, such as keyboards, are particularly constrained by this limitation.
This lack of flexibility is the primary reason just intonation was gradually replaced by temperament systems that allow for modulation.
Just Intonation Versus Equal Temperament
Compared to equal temperament, just intonation offers greater interval purity but far less harmonic mobility. Equal temperament slightly compromises every interval to ensure consistency across all keys, while just intonation perfects certain intervals at the expense of others.
These two systems represent different priorities rather than right or wrong solutions.
Use of Just Intonation Today
In Western music today, just intonation is most commonly used in:
Vocal ensembles
String ensembles without fixed pitch
Historically informed performance
Experimental and contemporary music
Performers in these contexts can adjust pitch in real time to maintain pure intervals.
