The concept of divided the octave into 12 tones which to avoid unpleasant harmonies. counterpoint equal temperament imitative polyphony modes

Equal temperament

Explanation: This system divides the octave in 12 semitones related by the sequence Fₙ₊₁ = Fₙ*2^(1/12) (in frequency).

In the actual American notation, the 12 semitones are called:

A, A#, B, C, C#, D, D#, E, F, F#, G, G#.

This new intonation is very useful to avoid unpleasant harmonies, but none the less, it still sounds a little bit "off" when compared with just intonation (in the right key).