Intonation has only been theorized extensively with respect to the role that it can play in maximizing harmonic consonance. The role of intonation in harmonic consonance is indeed important, but the degree of theoretical attention that has been focused on it is also due to the fact that intonation's other roles (key coloration, melodic meaning) are far more difficult to theorize about.
In addition to being focused on harmonic consonance, intonation theory has largely focused on static intonation. In static intonation, all of the notes in a piece that have the same pitch have the same frequency. Therefore static intonation conforms to a tuning, an assignment of frequencies to pitches. For example, ``do you like to play your middle C in measure 97 higher than in other measures?'' is a question about intonation whereas ``what frequency does middle C have?'' is a question about tuning. Instruments that must conform to a tuning, like the piano and organ, have static intonation. Thus it would not make sense to ask a pianist ``do you like play your middle C in measure 97 higher than in other measures?'' Although most pianists would not be sympathetic to the request, it does make sense to ask, ``can we tune your middle C higher, so that it sounds better in the context of measure 97, but not so high that has an adverse effect in other measures?'' Instruments like the violin and voice do not have to conform to a tuning and therefore can have dynamic intonation.
Static intonation (tuning) theory has had extensive practical application. The tuning and/or construction of all instruments with static intonation is based on the results of this theory. In contrast, dynamic intonation theory has not been put to practical use , , . In part this is because few performers have the skill to make such explicit intonation decisions worthwhile. For most modern performers, it more pragmatic to try to adhere approximately to static 12TET intonation most of the time, making on-the-fly adjustments by ear where necessary. Another reason why theories of dynamic intonation have not been put to use is that many theorists have focused on just intonation, a type of intonation that has maximally consonant harmonies but cannot accomodate the rich harmonic vocabulary of most Western music.