Every promise can be put either in a negative form or an affirmative form. Thus a promise to do any specific thing may be translated into a promise to refrain from doing anything else but that; and a promise not to do a particular act may be translated into a promise to be constantly occupied with other acts than the one in question. Nevertheless feasance differs from non-feasance, and a duty of inaction in whatever form it is put is in its essence negative. A promise of forbearance, therefore, though affirmative in form is in substance negative. Conversely a duty of action is affirmative though put in a negative form, as a promise not to discharge an employee. Moreover, a promise which is affirmative both in form and substance may cany with it not only an agreement to do what is specifically agreed, but by necessary implication an agreement not to do anything inconsistent therewith.52 It must be recognized, therefore, in any discussion of negative promises, that they are of four classes, namely:
49 Kemble v. Kean, 6 Sim. 333; Emberley v. Jennings, 6 Sim. 340; Baldwin v. Society for Diffusing Useful Knowledge, 95 Sim. 393; Hills 0. Croll, 2 Phillips, 60.
50 Donnell v. Bennett, 22 Ch. D. 835; Grimston v. Cnningham (1894), 1 Q. B. 125; William Robinson & Go. v. Heuer (1898), 2 Ch. 451.
51 See cases cited infra, Sec. 1450.
(1) Where the promise is expressly negative in form and substance;
(2) Where it is negative in substance but affirmative in form;
(3) Where it is negative in form but affirmative in substance;
(4) Where the negative promise is based merely on the implied obligation to refrain from doing anything inconsistent with an affirmative act which is promised.
In each of these cases, moreover, except the last the negative promise in question may constitute the promisor's sole undertaking in the contract or it may not. Where the negative promise is not the promisor's sole undertaking, its value to the promisee may be wholly dependent on performance of an affirmative undertaking, or it may have independent value. A promise to work for no one but the promisee has ordinarily no value except as part of the obligation to work for the promisee; but if the promisor has power to make himself hurtful as an aid to a competitor of the promisee, the negative promise has independent value. In cases of the latter sort as has been seen, injunctions are freely granted where damages afford inadequate redress.53 Where, therefore, a negative promise is the promisor's sole undertaking or has independent value, no further test is required; but in the third and fourth cases supposed above, the promisor is bound to positive action by the promise in question and there is no virtue in making a decree that the defendant shall refrain from doing anything else but that action, as compared with one affirmatively ordering him to do the act. If, for instance, equity is not prepared to enforce directly a contract of employment, it cannot properly enforce even an express promise of an employer not to discharge his employee, for that means the same thing.54 Therefore, it may be said that where the negative promise is in one of these last two classes, an injunction cannot be granted which is coextensive with the promise except when the character of the affirmative obligation is such that it would be specifically enforced as a whole; and in that case it would seem better to decree performance directly than by the roundabout means of an injunction.
"It is on this theory that implied promises not to prevent performance are based, (see supra, Sec. 1318); and also the doctrine of anticipatory breach, so far as it is explicable on any sound principle.
53See supra, Sec.1446.
54 Davis v. Foreman,  3 Oh. 654; Kirchner v. Gruban,  1 Ch. 413. See, however, as to the enforcement of affirmative obligations by negative decree, supra, Sec. 1423 ad fiss.