PRINCIPLE: A person is said to be of sound mind for the purpose of making a contract if, at the time when he makes it, he is capable of understanding it and of forming a rational judgment as to its effect upon his interests.
FACT: Mr. X who is usually of sound mind but occasionally of unsound mind enters into a contract with Mr. Y when he is of unsound mind. Y came to know about this fact afterwards and
now wants to file a suit against.