It necessarily follows from the power of the offeror to dictate the conditions of the contract, and the way that it may be accepted, that he may require the letter or telegram of acceptance actually to be received before a contract shall be formed.34 And it would seem a wise precaution for an offeror in making an offer by letter always to stipulate for actual receipt of the acceptance. This requirement need not be in express words, it is enough if the offer imposes a condition which cannot be satisfied until the acceptance is received. Thus, the words "If I do not hear from you by the 18th or 20th, I shall conclude, no," were held to impose a condition that the answer should be received by the 18th or 20th before a contract could be formed.35 So an offer by mail conditional "upon the return" of certain notes was held revocable at any time prior to their actual receipt.36