三者均为合同法中常用词。其中，promise是要约人向被要约人所作要约，为一种主动的“允诺”或“许诺”[1]。而acceptance 则为 “承诺”，是被要约人（offeree)对要约（offer) 的一种认可[2]。offer则与promise意思相同，是主动对他人的 “要约”[3];但与promise不同的是offer可以撤销（revocable); 而promise作为“允诺”则不能撤销[4]。

[1]“A party's undertaking about its future conduct. " Cf. G. H. L. Fridman, The Law of Contract in Canada，2 nd edition, at p. 1，Carswell (1986). " a declaration or manifestation ，esp. in a contract, of an intention to act or refrain from acting in a specified way that gives the party to whom it is made a right to expect its fulfillment." Cf. Linda Picard Wood, J. D.，Merriam Webster's Dictionary of Law, at p. 389, Merriam-Webster, Incorporated, Springfield, Massachusetts (1996).

[2] "An agreement, either by express act or by implication from conduct, to the terms of an offer so that a binding contract is fonned. ”Cf. Bryan A. Gamer, Black's Law Dictionary, 7th edition, at p. 11 , West Group (1999).

[3 ] "One person's indication to another that she or he is willing to enter into a contract with that person on certain terms. ” Cf. Daphne Dukelow, The Dictionary of Canadian Law, at p. 711, Thomson Professional Publishing; Canada (1991).

[4] Therefore, an offer is revocable, a promise is not. ” Cf. William R Arson, Some

Notes on Terminology in contract, 7 Law Q. Rev. at pp. 337, 337 (1891)