I may be wrong in my assumption, but I believe that Gorgias would say that music is not rhetoric.  In Plato’s Gorgias before Socrates asks, “With what is rhetoric concerned,” he asks Gorgias to confirm that “. . . music is concerned with the composition of melodies. . .” Gorgias confirms and then later again confirms that, “As to the arts generally . . . proceed in silence; and of such arts I suppose you would say that they do not come within the province of rhetoric.”

Gorgias believes that areas of study that are wholly influenced by words and words alone are to be considered rhetoric.  He believes that arts such as arithmetic, astronomy and medicine are all rhetoric but music which, to him, is simply notes emitted from an instrument does not involve discourse. That being said, if we use only the second part of Gorgias’ definition of rhetoric, the part about persuasion, we are then able to classify music as rhetoric.

People listen to different types of music when they are in different moods, when they want to change how they are feeling or depending on the situation that they may be in.  By changing the style of music to match the desired mood, we are accepting that the music has an effect on how we feel and therefore can ‘persuade’ us to feel differently.  Given this effect music, be it vocal or instrumental, can be argued to be just as much rhetoric as a public speaker who is attempting to change the audience’s view or mood.