silence is not enough, harsh, 'acceptance via silence' is not a valid form of acceptance, unfair, Felthouse v Brindley
verbal/written acceptance - provides evidence of offeree's intentions clearly, protects parties, fair
unilateral offers - acceptance via performance, exception to communication, offeror will be unaware of conduct, unfair, Carlil v Carbolic Smokeball Co
Law Commission 1975 - offer that the offeror has said will be open for a specific period should not be revocable within that period