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 cannot be composed by ordinary composer 
( z1 possible :polarity - :ARG1 ( z2 compose :ARG0 ( z3 person :ARG0-of ( z4 compose ) :mod ( z5 ordinary ) ) :ARG1 ( z6 harmony :mod ( z7 part :quant 4 ) ) ) )