Brain or Brains?

My wife and a good friend recently engaged in a friendly argument over the use of the word "brain." The friend claimed that the word may only ever be used in singular form. If she meant as used for the "...mass of soft gray matter in the skull," my wife's friend is correct when we are speaking formally. "Albert Einstein possessed a good brain." It is more "dignified" to use the singular brain to describe the qualities of wit or smartness (Fowler's Modern English Usage).

However, when describing someone informally as witty, clever, or smart, we tend to use the plural brains. If my wife was thinking of choice based upon circumstance, then she is correct. In informal, familiar situations, use the plural brains.

"Adam Sandler is a comedian with brains." Note, a useful adjective exists for our use: brainy. "Dick Cavett, a talk show host in the 1970's, proved a brainy interviewer."

Fowler also tells us that some phrases only permit use of singular or plural. No choice exists whether speaking formally or informally. You would never describe a melody that won't leave your head saying, "I can't get that tune out of my brains. " Nor would you say, "The man blew his brain out."