change one’s tune, to

To reverse one’s views, change one’s mind, switch sides in a controversy. The analogy is very old; John Gower wrote, c. 1394, “Now schalt thou singe an other song,” and the actual phrase, “change your tune,” appears in a ballad about Robin Hood (one of the Child ballads) from about 1600. And a character in Samuel Beckett’s novel, The Unnameable (1953), says, “I have my faults, but changing my tune is not one of them.”