The correct theory to apply in this situation is the expedition theory (also known as the postal rule). According to this rule, when acceptance is sent by post, the contract is concluded the moment the acceptance letter is posted by the offeree, not when it is received by the offeror. In the scenario:
- X sends a written offer by post to Y.
- Y reads the offer on May 13 and drafts an acceptance on May 14.
- Y posts the acceptance letter on May 15.
- X receives the acceptance on May 17 and reads it on May 18.
Under the postal rule, the contract is formed on May 15, the date when Y posted the acceptance. The fact that X only receives and reads the acceptance later does not affect the timing of contract conclusion. Other theories like the reception theory (contract concluded on acceptance receipt) or information theory (contract concluded when offeror reads acceptance) do not apply here because posting the acceptance creates a binding contract at that moment under the postal rule. This rule balances the risks between offeror and offeree in remote communications by placing the risk of postal delays on the offeror. Hence, the contract between X and Y was concluded on May 15, the date of posting Y's acceptance.
