User:Wahoofive/Key (music)

In music theory, the key of a piece usually refers to the tonic chord, which gives a subjective sense of arrival and rest. Other chords in the piece create varying degrees of tension, resolved when the tonic chord returns. The key may be major or minor, although major is assumed in a phrase like "this piece is in C." Popular songs are usually in a key, and so is classical music during the common practice period, about 1650-1900. Longer pieces in the classical repertoire may have sections in contrasting keys.

The methods by which the key is established for a particular piece are not easy to explain, and vary considerably over the period of music history; however, the chords most often used in a piece in a particular key are those containing the notes in the corresponding scale, and conventional progressions of these chords, particularly cadences, serve to orient the listener around the tonic.

Less commonly, pieces in modes such as phrygian and dorian may be referred to as the "key", or a piece using some other type of harmony might be described as "in A" to indicate that A is the central note of the piece; more often, the phrase tonal center is used in the latter case.

An instrument may be said to be "in a key", an unrelated usage meaning it is a transposing instrument.

A key relationship is the relationship between keys, measured by common tones and nearness on the circle of fifths. See: closely related key.