Intonation has two essential sides. The first is expressive intonation: music, like speech, carries questioning, affirming, and dramatic inflections. The same notated sentence, in different hands, can sound like hope or like despair — depending on how it is “spoken.”
The second is technical intonation, the accuracy of pitch. On the violin, viola, cello, or wind instruments, “clean intonation” is the product of years of honed hearing and muscle memory. Out-of-tune playing (even a hair's breadth off) mercilessly wounds the professional ear. In choral singing, intonation is both the unified sound and the living breath of the ensemble.
