If you Play It By Ear you take a situation as you find it and then adapt your actions to it. The idiom can be traced back to the time before sound recording equipment. In those days, composers and songwriters had to create a piece of music on a piano and write it down as they went along in order to remember how the melody went. Musicians, as well, had to listen to the instruments and then pick out their parts by ear, and this was known as “playing it by ear”. Nowadays, musicians who can play their part just by listening to a record are said to be playing it by ear.