Harmony (music)

Harmony in music is the practice of blending different sounds to generate fresh musical ideas. Theories of harmony aim to explain the effects that occur when distinct pitches or tones sound together, identifying and categorizing harmonic elements like chords, textures, and tonalities. Harmony is generally understood to have both a "vertical" aspect (related to frequency) and a "horizontal" aspect (related to time), and it often intersects with other musical concepts such as melody, timbre, and form. A strong focus on harmony is a key foundation of Western music theory and practice. Studying harmony involves placing individual pitches together to form chords, and then arranging those chords into larger progressions. The rules governing these structures have been explored through centuries of theory and practical music-making.

The perception of harmony draws from both music theory and psychoacoustics, largely involving the recognition and processing of consonance. The exact definition of consonance has shifted over time, but it is often linked to simple mathematical ratios between the frequencies of simultaneous pitches. From a physiological standpoint, consonance is seen as a continuous variable that measures how well the brain can decode auditory input. Culturally, consonant pitch relationships are typically described as more pleasant, euphonious, and beautiful, while dissonant relationships are often characterized as unpleasant, discordant, or rough.

In popular and jazz harmony, chords are named by their root note along with various terms and symbols indicating their qualities. In many musical styles—including baroque, romantic, modern, and jazz—chords are frequently expanded with "tensions." A tension is an extra chord member that creates a relatively dissonant interval against the bass. The concept of counterpoint seeks to understand the relationships between melodic lines, often within a polyphonic texture of several simultaneous but independent voices. For this reason, counterpoint is sometimes considered a type of harmonic understanding and sometimes treated as separate from harmony.

During the classical common practice period, a dissonant chord (one containing a tension) typically "resolves" to a consonant chord. Harmonization is generally perceived as pleasant when there is a balance between consonance and dissonance, creating a mix of "tense" and "relaxed" moments. Dissonance plays an important role in harmony when it can be resolved and contribute to the overall composition. A misplayed note or any sound judged to detract from the whole piece is described as disharmonious rather than dissonant.

The word harmony comes from the Greek *harmonia*, meaning "joint, agreement, concord," from the verb *harmozō*, "to fit together, join." Aristoxenus wrote *Elements of Harmony*, considered the first European work on the subject. In it, he references earlier Pythagorean experiments linking small integer ratios to consonant notes (for example, a 1:2 ratio describes an octave, which doubles the frequency). Although he identified as a Pythagorean, Aristoxenus argued that numerical ratios are not the ultimate basis of harmony; instead, he believed the listener's ear determines it.

Modern dictionary definitions often highlight the term's ambiguity, which arises from aesthetic considerations (such as the view that only pleasing sounds can be harmonious) or from the perspective of musical texture (distinguishing between harmonic, or simultaneous, pitches and contrapuntal, or successive, tones). According to A. Whittall, while music theory history seems to rely on a clear distinction between harmony and counterpoint, developments in musical composition have shown the interdependence—sometimes integration, sometimes tension—between the vertical and horizontal dimensions of musical space.

It is common in music theory to say that modern tonal harmony in Western music began around 1600, often explained by a shift from horizontal (contrapuntal) composition, typical of the Renaissance, toward a new focus on the vertical element. However, modern theorists often see this as an oversimplification. As Carl Dahlhaus put it, counterpoint was not replaced by harmony (Bach’s tonal counterpoint is just as polyphonic as Palestrina’s modal writing), but rather an older type of both counterpoint and vertical technique gave way to a newer one. Harmony includes not only the vertical structure of chords but also their horizontal movement; like music itself, harmony is a process.

Descriptions and definitions of harmony often show a bias toward European (or Western) musical traditions, even though many cultures practice vertical harmony. South Asian art music (Hindustani and Carnatic music) is frequently noted for placing little emphasis on what Western practice calls conventional harmony; the underlying harmonic foundation for most South Asian music is the drone—a sustained open fifth or fourth interval that does not change pitch throughout a composition. Simultaneous pitches are rarely a major focus, though many other pitch-related considerations remain important.