If the formation of a simple contract depended upon the existence of mutual assent in fact in the minds of the contracting parties, a change of mind on the part of either one before the requisite mutual assent was reached would prevent the formation of the contract.46 No case, however, goes so far as to hold material a change of mind on the part of the offerer not manifested by an over act,47 but several cases near the beginning of the nineteenth century show that the conception of the court at that time was that a manifestation by an overt act of a change of mind on the part of the offerer would operate as a revocation, though not communicated to the other party.48 This conception has found expression in the Civil Code of California,49 which, though providing for communication of "notice of revocation," also provides not only with reference to acceptance but also with reference to revocation 50 that communication is complete when put in course of transmission.51 At the present day, however, it is almost universally settled that a revocation requires communication and that, therefore, an acceptance prior to a communicated revocation will make a binding contract.52 It has been suggested that though manifest principles of justice require that a revocation should not be effectual against an acceptor of an offer until the revocation has been received, the revocation should bind by estoppel the offeror from the time when it was dispatched; but such a result could not be reached "without infringing upon the inexorable rule that one party to a contract cannot be bound unless the other be also, notwithstanding that the principle of mutuality thus applied may enable a party to take advantage of the invalidity of his own act."53 Revocation may be indicated by acts as well as words. Thus, after an offer of sale to one person, a sale of the same property to another person, if brought to the knowledge of the person to whom the offer was first made, will amount to a revocation.54 A revocation "should be as direct and explicit as the acceptance."55 What amounts to a receipt of a revocation must be the same as receipt of an acceptance, or other communication.56 Difficulties may arise where circumstances make it impracticable -to notify the offeree of revocation. Thus, the offeree may have gone to a distance from the mails, or his address may be unknown. It is perhaps still open to question whether the law should cast the burden upon the offeror who has put forth an offer or should adopt a rule analogous to that adopted in case of public offers,57 and hold the offer revoked if such an attempt is made to communicate a revocation in the same way that the original offer was communicated. Presumably, however, the burden would be thrown upon the offeror, unless the offeree purposely prevented communication.
44 A letter by one who had ordered advertising matter asking that it be not forwarded until he felt in a better condition to handle it was not a sufficient revocation of the order. Out-cault Advertising Co. v. Buell, 71 Or. 52,141 P. 1020.
45 Bellamy v. Debenham, 45 Ch. D. 481; Perry v. Suffields, limited 11916], 2 Ch.D. 187. See also infra,Sec.Sec. 81,82.
46flee infra, Sec.Sec. 95, 1630, 1537.
47See, however, supra, Sec. 60.
48In Cooke v. Oxley, 3 T. R. 653, where an offer to sell tobacco was made by the defendant, and the court held no contract was created by an acceptance later in the day, though within the time specified in the offer, Duller, J., said that "it is not stated that . . . the goods were kept until that time," evidently supposing that a sale of the goods, though without notice, would revoke the offer. The same implication is made in-Adams v. Lindsell, 1 B. & Ald. 681; Head v. Diggon, 3 M. & R. 97; Hebb's Case, L. R. 4 Eq. 9; Routledge v. Grant, 4 Bing. 653.
49Sec. 1587. The code was adopted in 1872.
50 Sec. 1583.
51 No decision has yet been made in California upon the matter, but in Walters v. Lincoln (So. Dak.), 135 N. W. 712, it was held under similar provisions in the South Dakota Code, Sec.Sec. 1212, 1215, 1216, that a revocation of an offer was effected as soon as deposited in the post-office.
52 Stevenson v. McLean, 5 Q. B. D. 346; Henthom v. Fraser,  2 Ch. 27; Re London & Northern Bank (1900] 1 Ch. 220; Tayloe v. Merchants' Fire Ins. Co., 9 How. 390, 13 L. Ed. 187; Patrick v. Bowman, 140 U. S. 411, 424, 37 L. Ed. 790; The Palo Alto, 2 Ware, 343; Weld v. Victory Mfg. Co., 205 Fed. 770; Kempner v. Cohn, 47 Ark. 519, 1 8. W. 869, 58 Am. Rep. 775; Sherwin v. Nat. Cash Register Co., 5 Col. App. 162, 38 Pac. 392; Wheat v. Cross, 31 Md. 99, I Am. Rep. 28; Brauer v. Shaw, 168 Musts. 198, 46 N. E. 617, 60 Am. St. Rep. 387; Peck v. Freese, 101 Mich. 321, 59 N. W. 600; Farmers' Handy Wagon Co. v. Newcomb, 102 Mich. 624, 159 N. W. 152; Pennsylvania 4 Delaware Oil Co. v. Klipstein, 175 N. Y. S. 540; Malloy v. Drumheller, 68 Wash. 106, 122 Pac. 1005.
53 Patrick v. Bowman, 140 U. S. 411, 424,37 L. Ed. 790.
54 Thurber v. Smith, 25 R. I. 60, 54 Atl. 790. See also Larmon v. Jordan, 56 111. 204; Wardell v. Williams, 62 Mich. 50, 28 N. W. 796, 4 Am. St. Rep. 814, and cases in the following section.
55 Linn v. McLean, 80 Ala. 360, 366.