because I'm a computer
They can speak.
you cant
she cant
mute
Dysphagia
Well you cant really speak when you have lost your voice, but if you try to speak it will get worse.
say meow meow :P you cant actually speak cat
Incoherant.
because they cant speak English ;)
I cant
you cant
If someone is unable to speak, it's called being 'dumb'.