A deafened character cannot hear. He takes a –4 penalty on initiative checks, automatically fails Perception checks based on sound, takes a –4 penalty on opposed Perception checks, and has a 20% chance of spell failure when casting spells with verbal components. Characters who remain deafened for a long time grow accustomed to these drawbacks and can overcome some of them.

Marius, Scholai Armsmaster Says: Some abilities like the bard’s Inspire Courage ability or the Hideous Laughter spell require that the target be able to hear you.