“A composer creates from the realm of the unknown; a performer presents creation to the world. The two work separately or together in order to gift humanity with something wonderful. This symbiotic relationship also lives between the choreographer and the dancer, the chef and the cook, the playwright and the actor, the designer and the model. Sometimes they merge into one and bring into the world the Composer-Performer.

Question: Where does the arranger fit in this relationship?

Someone builds a sturdy house, but it’s just wood and blocks. The builder wants to make it marketable by enhancing its appearance. So he hires someone to paint it, install carpet, hang curtains, landscape it, etc. ,etc.

A record company has a great song that they want to market, but now it’s just a  vocalist accompanied by a rhythm section. They want to enhance the song by adding horns and strings; so, they hire an arranger. The arranger determines what instruments to use and writes the parts. The arrangement may include an intro, an instrumental interlude, melodies, harmony, countermelodies, riffs, modulations, reharmonizations, etc. In short, this is what an arranger does.