Section 4 of the Indian Contract Act, 1872, is titled "Communication when complete." It provides the crucial rules for determining the exact moment a contract is formed through correspondence. It states:
\[\begin{array}{rl} \bullet & \text{The communication of an acceptance is complete as against the proposer (offeror) when it is put in a course of transmission to him, so as to be out of the power of the acceptor. (This is the postal rule).} \\ \bullet & \text{As against the acceptor, the communication is complete when it comes to the knowledge of the proposer.} \\ \end{array}\]
Section 3 deals with communication generally, while Sections 5 and 6 deal with the revocation of proposals and acceptances.