Nothing is so agreeable to natural equity as that, by the like means by which anything is bound, it may be loosed.
It is said that there is no inheritance executory ; as rents, annuities, conditions, warranties, covenants, and such like ; but may, by a defeasance, made with the mutual consent of all those who were parties to the creation thereof, be annulled, discharged, and defeated. And so as to recognisances, obligations, and the like ; yet so as in all such cases the defeasance be made eodem modo, as the obligation ; viz., if the one be by deed, the other must be by deed also ; for it is a rule that in all cases where anything executory is created by deed, it may, by consent of all persons parties to the creation of it, be by deed defeated and annulled.
In accordance with this rule, it is laid down that an obligation must be avoided by release ; a record by record ; a deed by deed ; a parol promise by parol ; an Act of Parliament by an Act of Parliament ; every agreement or obligation being dissolved only by a like high agreement or obligation.
By the common law, a parol waiver is no discharge of a covenant : as, a covenant by A. not to carry on a particular business within a certain distance of the premises of D., cannot be discharged by a parol permission from D. to A., authorising him to carry on such business. And where by deed a lessee covenanted to yield up all erections and improvements upon the demised premises at the end of his term ; it was held that to remove a greenhouse he had subsequently erected thereupon was a breach of the covenant, notwithstanding a parol permission from the lessor so to do, made prior to the erection of the building.
So, a covenant to build a house, or to perform other like outage- merits within a limited time, is not discharged by parol. It is upon this principle that oral evidence is inadmissible to add to. alter, or vary, a written contract, though not under seal ; for, where there is no ambiguity in the words of a written contract, no exposition contrary to the written words will be received.
Before breach, the obligor of a bond for payment of a sum of money on a certain day, may discharge himself by showing payment on or before the day appointed, and acceptance in satisfaction by the plaintiff of a smaller for a larger sum, or of some other thing, as a horse or other goods, in whole or in part in lieu of money. After breach, anything paid in satisfaction is sufficient to be pleaded by way of accord and satisfaction in discharge of a contract, whether simple or special, or whether the remedy adopted be by action of covenant on deed, or action of assumpsit on parol agreement. The accord must, however, in all cases be executed — i.e., there must be an acceptance and receipt by the party entitled or claiming to be entitled under the contract. Prevention of performance will also operate as a discharge of a covenant ; as, if a man covenant to build a house upon the land of another, and the covenantee refuse to let the covenantor enter upon the land to build, in that case performance will be excused.
Formerly covenants under seal could not be discharged by parol before breach, whether executed or executory ; but now, an executed parol contract made in discharge of a covenant may be pleaded in equitable defence to an action on the covenant.
The whole principle of the maxim is founded upon the question of consideration : a contract requiring a consideration to make it requiring also a consideration to break it.
2 Inst. 35!) ; Shepp. Touch. 396 ; 2 Roll. Rop. 39 ; Litt. s. 34-4 ; Go. Litt. 213; Pothier Obi. 785; 6 Co. 43, 44; Sellers v. Bickford, 1 Moore, 460; West v. Blakeway, 3 Sc. N. R. 199 ; Spenee v. Healey, 8 Exoh. 688; Cdrd- went v. Hunt, 8 Taunt. 596 ; Lord Petrie v. Stubbs, 25 L. T. 81 ; Geo v. Smart, 26 L. J. 305, Q. B. ; Smith v. Bahama, 26 L. J. 232, Ex. , Fosf.pr “. Dawbar, 6 Exch. 839; 17 & 18 Vii-'t. … 125.