Where a plaintiff seeks specific performance of a contract in writing, to which the defendant sets up a variation, the plaintiff cannot obtain the performance sought, except with the variation so set up, in the following cases, namely:—
(a) where by fraud, mistake of fact or misrepresentation, the written contract of which performance is sought is in its terms different from what the parties agreed to, or does not contain all the terms upon which the contract was made;
(b) where the object of the parties was to produce a certain legal result which the contract as framed is not calculated to produce;
(c) where the parties have, subsequently to the execution of the contract, varied its terms.
Legal Commentary & Landmark Judgments: Section 18
Section 18 of the Specific Relief Act, 1963 regulates non-enforcement except with variation, establishing that where a plaintiff seeks specific performance of a contract in writing to which the defendant sets up a variation (due to fraud, mistake, or misrepresentation), the plaintiff cannot obtain enforcement without that variation.
If the written agreement omitted an agreed grace period or cash advance condition due to drafting haste, plead the true oral collateral agreement under Section 18; the court will refuse to enforce the agreement without your pleaded variation.