Contract law for non lawyers course

What are the 4 requirements for a valid contract?
The law of contract is the most important part of mercantile law in India.
It determines the circumstances in which the promise made by the parties to a contract shall be binding on them and provides for the remedies available against a person who fails to perform his promise..
What is acceptance in contract law?
What is acceptance? According to the Indian Contract Act, 1872, Section 2(b), acceptance is expressed as “When the person to whom the proposal has been made signifies his assent thereto, the offer is said to be accepted.
Thus, the proposal when accepted becomes a promise.”.

What are the 4 requirements for a valid contract?