Why did equal temperament replace earlier European tuning systems?

Equal temperament replaced earlier European tuning systems, such as meantone temperament and just intonation, primarily because it enabled instruments with fixed intonation—like keyboard instruments—to play in all keys with minimal flaws.1

Earlier "cyclic" systems relied on acoustically pure intervals that accumulated intonational errors when transposed to distant keys. This often resulted in "wolf" chords—highly dissonant intervals that made certain keys unusable. As Western music evolved to require greater freedom in tonality, chromaticism, and enharmonic modulation, these limitations became increasingly restrictive.123

Equal temperament solved these issues by dividing the octave into 12 equal semitones. While this requires sacrificing perfectly pure intervals (except for the octave), it distributes small intonational defects equally across all 12 tones. This uniformity allows for the expanded harmonic range characteristic of 19th- and 20th-century music and provides a consistent framework for tuning and temperament that remains central to Western musical consciousness today.123