harmony (as a discipline); laws of harmony
Refers to the study or system of rules governing harmony in music, not a single law. Used in academic or music theory contexts.
I study harmony at the music college.
This textbook explains the basics of harmony.
Compound of 和声 (わせい, 'harmony') + 法 (ほう, 'method' or 'law'). The term is a modern coinage for Western music theory.