What is a sound mind for the purposes of contracting
Chapter 3: Of contracts, voidable contracts and void agreements
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. A person who is usually of unsound mind, but occasionally of sound mind, may make a contract when he is of sound mind. A person who is usually of sound mind, but occasionally of unsound mind, may not make a contract when he is of unsound mind.
Illustrations.
(a) A patient in a lunatic asylum, who is at intervals of sound mind, may contract during those intervals.
(b) A sane man, who is delirious from fever or who is so drunk that he cannot understand the terms of a contract, or form a rational judgment as to its effect on his interests, cannot contract whilst such delirium or drunkenness lasts.
The Indian Contract Act, 1872 (Act No. 9 of 1872). From the updated text on India Code, with later amendments. Being checked against the official copy; amendment notes are not shown yet.