Specifically, what Berkeley was asserting was that the existence of the acoustic vibrations (although I don't think he knew that they were vibrations) was dependent upon the existence of the auditory experience. It wasn't an argument about definitions at all! It was a peculiar kind of solipsism which, as Rosser guessed, I have little sympathy with.

Maybe you should try telling some parables about people who thought they had certain knowledge. Maybe some of them should include other people who did not think their knowledge was certain.