Harmony results from simultaneous sounds. It creates the impression of polyphony and triggers, on the part of the listener, different sensations according to conscious or unconscious esthetic conceptions. These conventions are called harmonic rules. In the Western view, harmony is the most developed part of music theory. Harmony forms the vertical texture of a piece, whereas melody and rhythm form its horizontal texture. In music, harmony is realized through chords.

Metaphorically said,

melody is the body, and harmony is the clothes that change with fashion.¹⁾

However, every idea of harmony is obviously bound to psychoacoustic phenomena:

It would indeed seem difficult to discover any other basis for a harmonic theory claiming to be universal.²⁾

In traditional music theory, the effect of sound sequences on the sensations (emotions) of the listeners have frequently been linked to the tonalities and harmonies use. However, as Johann Joachim Quantz already stated, these associations are not unavoidable:

There is no consensus concerning the effects of certain tonalities, be they major or minor. Our ancestors thought that each key had its proper character and proper expression of emotions. As the scales were not the same in their keys …; and as therefore almost every key had its own types of cadences, this opinion was fairly profound. In our days, however, where the scales of all big and small keys are similar, it is questionable if the properties of the keys are still like that. Some are still supporting the opinion of our ancestors; others however deny it und proclaim that each passion can be expressed in one key as well as in any other, if only the composer is able to do so. It is true, we have examples for this; there is proof that some have succeeded in very aptly expressing an emotion in a key that does not really seem to be most convenient for it. But who knows if the same piece, set in a different and more fitting key, was not even more efficient?³⁾

Accordingly, European musicians have arrived at conflicting and ambiguous judgments about different tonalities:

In many cases, however, these ascriptions result from musical performance conventions rather than being innate musical temperaments:

For example, brass instruments are in a certain tuning: horns of old in F, trumpets in D … These instruments sound best in „their“ keys. Anyone who wanted to compose festive music with timpani and trumpets, used to choose D major almost always, hence the reputation of this key to shine brilliantly. In some keys, the character attributed to them emancipated from its original instrument-practical reasoning: From the custom to let all the instruments play mourning music with dampers, the fame of E major arose to be a mourning sound; as trumpets played with dampers sound a note higher, they then stand in E instead of in D.⁴⁾

Another approach is pursued by Daniela and Bernd Willimek's Theory of Musical Equilibration, which traces the effects of music to the „identifications of the listener with volitional processes“. The Willimeks define Equilibration as „identification with a will against change.“⁵⁾ In major chords, the listener feels a certain tension, but agrees with it; however, he does not emotionally agree with minor chords. „The experience of listening to a minor chord corresponds to the information one receives when someone says I've had enough.“⁶⁾ Through a self-constructed test on more than 2000 adolescent participants, Willimek and Willimek determined the effects of certain chords to be universal.

• Wolfgang Lempfrid: Tonartencharakteristik
• Daniela and Bernd Willimek: Musik und Emotionen: Studien zur Strebetendenz-Theorie. First edition 1997.