The term "four-part harmony" refers to music written for four voices or for some other musical medium—four musical instruments or a single keyboard instrument, for example—where the various musical parts can give a different note for each chord of the music.
Four-part harmony is long tradition of music
( z1 harmony :mod ( z2 part :quant 4 ) :mod ( z3 tradition :ARG1-of ( z4 long ) :mod ( z5 music ) ) )