why must billy stutter?

Billy seems to have it all. He is good looking, athletic, friendly and adventurous. People gravitate to him. Billy is, however, naive. He approaches life with the mindset of a boy. He feels that everybody has good intentions towards him. Melville gives Billy a speech impediment as part of his weakness. It is directly related to his naiveté and innocence. Billy is caught off guard when John Claggart accuses him of mutiny. Not only does Billy not comprehend evil and deceit, he cannot verbally defend himself either. The speech impediment is very much a part of Billy's Achilles heel.