consent & Consideration is must for valid contract

What agreements are contracts - All agreements are contracts if they are made by the free consent of parties competent to contract, for a lawful consideration and with a lawful object, and are not hereby expressly declared to be void. Nothing herein contained shall affect any law in force in India and not hereby expressly repealed by which any contract is required to be made in writing or in the presence of witnesses, or any law relating to the registration of documents.

Who are competent to contract - Every person is competent to contract who is of the age of majority according to the law to which he is subject, and who is of sound mind and is not disqualified from contracting by any law to which he is subject.

What is a sound mind for the purposes of contracting - 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.

“Consent” defined - Two or more persons are said to consent when they agree upon the same thing in the same sense.

“Free consent” defined - Consent is said to be free when it is not caused by— 

(1) coercion, as defined in section 15, or 

(2) undue influence, as defined in section 16, or 

(3) fraud, as defined in section 17, or 

(4) misrepresentation, as defined in section 18, or 

(5) mistake, subject to the provisions of sections 20, 21 and 22. 

Consent is said to be so caused when it would not have been given but for the existence of such coercion, undue influence, fraud, misrepresentation or mistake.