The concept of tonality originated in the Renaissance and was established in the Baroque period. It is related to the use of major and minor scales.

When a piece is built on a major or minor scale, the tonic of that scale becomes the tonal centre. The piece is based on that note: the piece is in the tonality or key related to that scale. For example, if the scale is a major scale of D, the key is D major.

In the musical pieces written during the Baroque, Classical and Romantic periods, the key is meant as the main key. However, many modulations (temporary changes of key) occur throughout the piece.

Chords, especially dominant seventh chords, help to define tonality and modulation.

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