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.

Facts: Mr. X who is usually of sound state of mind, but occasionally of unsound state of mind, enters into a contract with Mr. V when he was of unsound state of mind. Mr. Y having come to know about this fact afterwards wants to file a suit against Mr. X