Strictly a contract can be enforced either in law or in equity only against the party who entered into it. Only a promisor can be required to keep a promise; but where a promise relates to property equity fastens an obligation upon any one who receives the property either with knowledge of a duty owing by his grantor in regard to it or without consideration. The enforcement of an obligation against one who has obtained a conveyance of property which his grantor had contracted to sell to another, if the grantee is not a bona fide purchaser for value, illustrates this. On this principle equity is enabled to enforce contracts to leave property by will. Though such contracts cannot be strictly enforced after the death of the promisor, those who receive his property as heirs, personal representatives, devisees, or legatees if merely volunteers, can be compelled to convey it to the promisee.85 But the consideration of such exercise of equitable powers belongs rather to a treatise on the law of trusts than to one on the law of contracts.
The cases of imposition of an equitable obligation analogous to a contract are not, however, confined to cases of trusts. Though cases are not frequent where direct enforcement of a positive contractual obligation can be given against one who has not entered into a contract unless a res is concerned to which equity can attach the character of a trust, or something analogous, negative stipulations of such a character that they would be enforced by injunction against the promisor may also be enforced by injunction against one who by his dealings with the promisor is inducing or forcing the latter to break them.86 So where one has contracted not to engage in a certain business, others may be enjoined from employing him in that business or associating themselves in it with him.87 And other illustrations of this jurisdictions of equity may be found.88 These cases may, however, be regarded as illustrative of that principle of the law of torts, which prohibits unwarranted interference with the contracts of others.89
82 Enforcement of Negative Covenants, 4 Cal. Law Review, 114, 130.
83 1 De G. M. & G. 604. 84 See supra, Sec.1460. 85 See supra, Sec.1421.
86 In De Mattoe v. Gibson, 4 De G. & J. 276, one C had agreed that his vessel should carry a cargo to Sues, but later mortgaged the vessel to G, who had knowledge of the charter. The court held that though it could not specifically enforce a contract to make the agreed voyage, it could restrain the employment of the vessel in a different manner. Though the court declined to issue an injunction against G, under the particular facts of the case, it intimated that the conduct of the mortgagee, in interfering with the charter, might be such as to justify an injunction against him. See also Messageries Imperiales Co. p. Baines, 7 L. T. Rep. 763.
87 Fleckenstein Bros. Co. v. Flecken-stein, 66 N. J. Eq. 252, 57 Atl. 1025; Booth v. Seibold, 37 N. Y. Misc. 101, 74 N. Y. S. 776.
88 See "Equitable Rights and Liabilities of Strangers to a Contract" by Harlan F. Stone, 18 Columbia L. Rev. 291.
89 See Posner Co. v. Jackson, 223 N. Y. 325, 332, 119 N. E. 573, and cases cited.