2. Upon statutory, official, or customary duties.
3. Upon the doctrine that no one shall be allowed to enrich himself unjustly at the expense of another. The latter is the most important and most numerous class. See also Ans. Contr. 6th ed. 7; 2 Harv. L. Rev. 64; Louisiana v. New Orleans, 109 U. S. 285, 3 Sup. Ct. 211, 27 L. Ed. 936.
A claim for half-pilotage fees under a stat ute allowing such fees, where a pilot's serv ices are offered and declined, is an instance of a quasi-contract of the second class ; Pa cific Mail S. S. Co. v. Joliffe, 2 Wall. (U. S.) 450, 17 L. Ed. 805. See also Milford v. Com., 144 Mass. 64, 10 N. E. 516. Prof. Keener, in his work above cited, considers the duty of a carrier to receive and carry safely as being of a quasi-contractual nature. Among the third class are also cases of the liability of a husband to pay for necessaries furnished to his wife ; of a father for' those furnished to his child. Also cates of actions to recover money paid under a ,wistake ; actions in as sumpsit against a tort:feasor, where the tort is waived ; actions to recover compensation for benefits received under a contract which the plaintiff cannot enforce because he has failed to comply with the conditions thereof ; actions for benefits conferred by the plain tiff under a contract which the defendant, reason of the statute Of fraudg, illegality, impossibility, etc., is" not bound to perform; actions for benefits conferred on the defend ant at his reqUest, but in the absence of a contract ; actions for benefits intentionally conferred, but without the defendant's re quest ; actions for money paid to the use of the defendant ; and actions for money paid under compulsion of law and money paid to the defendant under duress, legal or equita ble. These are the general classes giiren in Keener, Quasi-Contracts, to which reference is made, passim,. The question to be deter mined is not the defendant's intention, but what in equity and good conscience the de fendant ought to do. The action of indebi tatus assumpsit was extended to most cases of quasi-contracts; Harriman, Contr. 24; 2 Harv. L. Rev. 63. The settled tendency of English and American law is toward a new classification of contracts and the treatment of implied contracts upon the lines here in dicated. They are lines clearly defined in the Roman law as shown by Maine (Anc. Law, 3d. Am. ed. 332), who is extensively quoted by Keener. See CoNTAcTuAr., OBLI GATION ; Woodward, Quasi-Contracts.
Negotiations preceding a contract. Where there is an agreement between parties to en ter into a contract in the and any essential part of the contract is left open, the agreement does not constitute a contract' in itself ; Sibley v. Felton, 156 Mass. 273, 31 N. E. 10. Such is the case also if the agree ment itself shows that it was not intended, to bind the parties, but that a formal contract was to be executed; Eads v. City of Caronde let, 42 Mo. 113 ; 70 L. T. 781. But a mere reference to a contract to be drawn up in the future is not conclusive that the parties are not bound by their original agreement, though- it tends to show that such is the Allen v. Chouteau, 102 Mo. 309, 14 S. W. 869; L. R. 18 Eq. 180. The question is one of intention to be gathered from the original' agreement, in view of all the cir cumstances ; Sanders v. Fruit Co., 144 N. Y. 209, 39 N.E. 75, 29 L. R. A. 431, 43 Am. St. Rep. 757; Harriman, Contr. 52.
Where negotiations are made "subject to the preparation and approval" or "comple tion of a formal contract," they do not con stitute a binding contract, whether the con dition is expressed in the offer ; [1895] 2 Ch.
1844 ; or in the acceptance; 7 Ch. D. 29 ; but "the mere reference to a future con tract is not enough to negative the exist ence of a present one ;';, 8 Ch. D. 70. Where a baker sold, and a company bought a shop, and the contract seemed complete in two letters, but afterwakd the company wrote a third letter introducing a new and vital term, viz., a restriction upon the baker's trading in the district, it was held that the three letters read together negatived the idea that the two letters constituted the con tract ; 42 Ch. D. 616. Where the acceptance was "subject to the title being approved by our solicitor" it was held, that this meant no more than the liberty which every pur chaser impliedly reserves to himself of breaking off the contract if the vendor breaks it, by not making a good title. The Court of Appeals construed these words as a condition, but Lord Cairns, L. C., pointed out that they would, if so construed, imply that the vendor was free, but the purchaser bound; 4 App. Cas. 311. In 3 App. Cases 1124, in the House of Lords, it was said, in holding that a correspondence between par ties constituted a complete contract, "If you can find the true and important ingredients of an agreement in that which has taken place between two parties in the course of a correspondence, then, although the corre spondence may not set forth, in a form which a solicitor would adopt if he were instructed to draw an agreement in writing, that which is the agreement between the parties, yet, if the parties to the agreement, the thing to be sold, the price to be paid, and all those mat ters, be clearly and distinctly stated, al though only by letter, an acceptance clearly by letter will not the less constitute an agreement in the full sense between the par ties, merely because that letter may say, `We will have this agreement. put in due form by a solicitor.' " In the same case Lord Blackburn said that there must be a complete agreement, "if not there is no con tract so long as the parties are only in nego tiation. But the mere fact that the parties have expressly stipulated that there shall afterwards be a formal agreement prepared embodying the terms which shall be signed by the parties, does not by itself show that they continue merely in negotiation. It is a matter to be taken into account in ing the evidence and determining whether the patties have really come to a final agree ment or not." The tendency in recent authorities is said in Pollock, Contr. 47, to discourage all at tempts to lay down any fixed rule as govern ing these cases. The question may be made clear by putting it this way, there is in the particular case a final consent of the parties such that no new term or varia tion can be introduced in the formal docu ment to be proposed. "It is a settled law' that a contract may be made by letter and that the mere reference in them to a future formal contract will not prevent their con stituting a binding contract ;" 8 Ch. D. 70: It is not binding if the terms are uncertain, e. g., an agreement to sell an estate ing "the necessary land for making a rail road" ; [1875] 20 Eq. 492; to make such a contract in the future "as the parties may agree upon" ; Shepard v. Carpenter, 54 Minn. 153, 55"N. W. 906; to give a lease in the form usual in the city where the property is situate; Scholtz v. Ins. Co., 100 Fed. 573, 40 C. C. A. 556; otherwise of an agreement to execute a deed of separation containing the "usual covenants" ; [1881] 18 Ch. Div. 670.