If you want to say that a person is crazy, you have to try long and hard to come up with a way of expressing this idea without using a metaphor. To say that the person has gone crazy is already to use a metaphor. “Crazy” comes from the word “crazing” which is the system of tiny cracks that can begin to appear in the glaze of an otherwise and heretofore perfectly good piece of pottery. Apparently someone, sometime looked at a person who was going crazy and was reminded of a glazed pot that was beginning to craze, and they used the phrase “He is becoming crazed” even though he knew it wasn’t literally true. And to say a person has “gone crazy” is to mix two metaphors. He is sitting right in front of you, so he hasn’t gone anywhere literally. And he is not a pot with glaze, so he is not crazed. So he has not literally gone crazy, even though he has gone crazy.
What is “crazy” ?2 06 2013