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.
A violin can not be used for four-part harmony
( z1 possible :polarity - :ARG1 ( z2 use :ARG1 ( z3 violin ) :ARG2 ( z4 harmony :mod ( z5 part :quant 4 ) ) ) )