Harmony

a. The study of the structure, progression, and relation of chords.
b. Simultaneous combination of notes in a chord.
c. The structure of a work or passage as considered from the point of view of its chordal characteristics and relationships.
d. A combination of sounds considered pleasing to the ear.

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Harmony
From Wikipedia, the free encyclopedia

The harmonious major triad is composed of three tones. Their frequency ratio corresponds approximately 6:5:4. In real performances, however, the third is often larger than 5:4. The ratio 5:4 corresponds to an interval of 386 cents, but an equally tempered major third is 400 cents and a Pythagorean third with a ratio of 81:64 is 408 cents. Measurements of frequencies in good performances confirm that the size of the major third varies across this range and can even lie outside it without sounding out of tune. Thus, there is no simple connection between frequency ratios and harmonic function.
In music, harmony is the use of simultaneous pitches (tones, notes), or chords.[1] The study of harmony involves chords and their construction and chord progressions and the principles of connection that govern them.[2] Harmony is often said to refer to the "vertical" aspect of music, as distinguished from melodic line, or the "horizontal" aspect.[3] Counterpoint, which refers to the interweaving of melodic lines, and polyphony, which refers to the relationship of separate independent voices, are thus sometimes distinguished from harmony.
Definitions, origin of term, and history of use

The term harmony derives from the Greek ἁρμονία (harmonía), meaning "joint, agreement, concord",[4] from the verb ἁρμόζω (harmozo), "to fit together, to join".[5] The term was often used for the whole field of music, while "music" referred to the arts in general.
In Ancient Greece, the term defined the combination of contrasted elements: a higher and lower note.[6] Nevertheless, it is unclear whether the simultaneous sounding of notes was part of ancient Greek musical practice; "harmonía" may have merely provided a system of classification of the relationships between different pitches. In the Middle Ages the term was used to describe two pitches sounding in combination, and in the Renaissance the concept was expanded to denote three pitches sounding together.[6]
It was not until the publication of Rameau's 'Traité de l'harmonie' (Treatise on Harmony) in 1722 that any text discussing musical practice made use of the term in the title, though that work is not the earliest record of theoretical discussion of the topic. The underlying principle behind these texts is that harmony sanctions harmoniousness (sounds that 'please') by conforming to certain pre-established compositional principles.[7]

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