In Western music, harmony is the use of different pitches simultaneously, and chords, actual or implied, in music. The study of harmony may often refer to the study of harmonic progressions, the movement from one pitch simultaneously to another, and the structural principles that govern such progressions. In Western Music, harmony often refers to the "vertical" aspects of music, distinguished from ideas of melodic line, or the "horizontal" aspect.Jamini, Deborah (2005). Harmony and Composition: Basics to Intermediate, p.147. ISBN-10: 1412033330. For this reason, considerations of counterpoint or polyphony are often distinguished from those of harmony, though contrapuntal writing of the common practice period of western music is often conceived and defined in terms of underlying harmonic motion.

Definitions, origin of term, and history of use

The term harmony derives from the Greek ἁρμονία (harmonía), meaning "joint, agreement, concord" and that from the verb ἁρμόζω (harmozo), "to fit together, to join". In Ancient Greek music, the term was used to define the combination of contrasted elements: a higher and lower note.

Nevertheless, the simultaneous sounding of notes was not part of musical practice in antiquity; harmonía merely provided a system of classification for 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.

It was not until the publication of Rameau's 'Traité de l'harmonie', in 1722, that any text discussing musical practice made use of the term in the title. The work is however by no means considered the earliest record of theoretical discussion of the topic. This and similar texts tend to survey and codify the musical relationships that were closely linked to the evolution of tonality from the Renaissance, to the late Romanic periods. The underlying principle behind these texts is the notion that harmony sanctions harmoniousness (sounds that 'please') by conforming to certain pre-established compositional principles. Arnold Whittall, "Harmony", The Oxford Companion to Music, ed. Alison Latham, (Oxford University Press, 2002) (accessed via Reference Online, 16 November 2007 is gayubview=Main&entry=t114.e3144 )

Current dictionary definitions, while attempting to give concise descriptions often highlight the ambiguity of the term in modern use. Such ambiguities tend to arise from either aesthetic considerations (espousing, for example, the view that only "pleasing" concords may be harmonious) or from the point of view of musical texture (distinguishing between harmonic, simultaneously sounding pitches and contrapuntal, successively sounding tones). In the words of Arnold Whitall: