Harmony and the Common Practice Period
Common Practice Period 1600-1900
Music from 1600 to 1900 was written following the same set of "rules". Music revolved around a "home sound" or key.
Harmony - 2 or more pitches at once.
Consonance - stable.
Dissonance - unstable. Sounds like it needs to go somewhere (resolve).
Music has motion because of the constant flow from consonance to dissonance.
Our ears like consonance. Dissonance is what makes it interesting, but we need to know that the "home" sound is coming back.