Well, people born deaf obviously can't talk as they'd be una ble to reference what they're saying against anything or how they should be saying something. As for people who become deaf, well in order to answer that try this: read my post and the ones before it in this thread only by moving your tongue/lips w/o using your vocal chords/throat or without making a sound. Your brain remembers how to make the sounds for a word, but without any way to double check the physical action of your tongue/throat you start to doubt whether you're doing it right. So speech is not possible in either case.