Tomas owns a home unit. It is unoccupied. Jozef tells Tomas (orally) he would lease the unit if Tomas instals air conditioning. Tomas orally agrees to this and two days later informs Jozef in an email that the air conditioning will be installed the following day. Jozef does not reply. The air conditioning is installed at a cost to Tomas of $4,500. Five days after that Jozef tells Tomas he has decided not to lease the unit. When Tomas says to Josef that a contract exists between them requiring Josef to lease the home unit Josef answers "there is no contract between us because there was no consideration paid by you to me."

Josef is right; no consideration was paid by Tomas to Josef (Tomas's payment was to the company installing the air conditioning). But Tomas could enforce their agreement by another legal principle. State the name of that legal rule or principle by which Tomas could enforce the agreement that Josef would lease the unit if air conditioning were installed, and briefly explain why it applies in this situation? [2 marks]