Intonation is the way frequencies are assigned to individual notes in the performance of a piece of music. Intonation must operate within a loose set of bounds that guarantee that the basic meaning of a piece will be preserved [3, 193-215], [14, 37], [20, 136-49]. For example, a minor third must be smaller than a major third. Within these bounds, intonation provides considerable expressive possibilities. The role of intonation in performing music is analogous to the role of pronunciation in reading poetry. Pronunciation operates within bounds that guarantee that the basic meaning of the poem will be preserved: for example, ``mole'' must be pronounced distinctly from ``male.'' Within these bounds, there is room for the speaker's accent, vocal quality, and emotional expression.
What are the expressive possibilities of intonation? Here are a few. Intonation can be used to ``color'' or give mood to music. Historically, there has been much interest in the way intonation can give different moods to music in different keys [24], for instance through the use of a class of tunings called well temperaments. Although the mood that intonation imparts does not ``happen'' at any given time, intonation does influence the meaning of specific musical events. An important melodic example concerns upward steps from pitches that function as leading tones. The higher the intonation of this leading tone, the more a pull towards the pitch above it is felt. Since the pitch above it typically functions as some kind of local tonic, this pull can help enhance cadences and establish tonality [17, 63]. Low leading tones tend to give a ``dull'' sound to the music. Intonation also has a profound effect on harmonic events. It can determine just how dissonant a dissonant harmony is, and just how consonant a consonant harmony is. Extreme consonances can be useful to promote a feeling of tranquility and resolution in music, and can serve to heighten contrasts with dissonances [12, 331].