This section is from the book "The Law Of Contracts", by Theophilus Parsons. Also available from Amazon: The law of contracts.
(cc) Houser v. Lamont, 55 Pa. 311.
(d) Townshend v. Stangrooin, 6 Ves. 328; Garrard v. Grinling, 2 Swanst. 244; Clowes v. Higginsou, 1 Ved & B. 524.
(e) When parties enter into a written, agreement, whether about a subject-matter within the statute of frauds or not, and at the time an additional provision is agreed upon, which by mutual consent and without fraud is not inserted in the writing, it is competent to either party to resist a specific execution of the, mere written agreement, by setting up the parol stipulation; but in such case, the plaintiff may have a decree, upon yet a plaintiff cannot have a decree for a specific performance of a written contract with a variation upon parol evidence. (f) And it is as a departure from this fundamental principle, that the doctrine that the court may at once reform a written contract, and proceed to enforce it as altered, has been resisted. Even when offered by the defendant, the proof that a written agreement does not contain all the terms of the contract should be very clear, (h)
* But the principal exception from the operation of the statute of frauds, is where the answer of the defendant states or admits all the facts on which the plaintiff's case depends, and does not interpose the defence of the statute of frauds, or the want of writing..(i) Whether this exception rests in any consenting to incorporate in the contract the unwritten agreement thus set up by the defendant. In other words, the written agreement, in a case of this kind, binds both at law and in equity, subject to the right of either party, when sued in equity, to ask the court to refuse its aid unless the plaintiff will consent to the performance of the omitted term. Martin v. Pycroft, 2 De G., M. & G. 785, 15 Eng. L. & Eq. 376, reversing s. c before Parker, V. C, 11 Eng. L. & Eq. 110. In Warren v Thunder, 9 Irish Eq. 375, the Lord Chancellor, considering that the plaintiff, in originally setting forth the contract, had not acted fairly, was indisposed to give him any relief at all; but, inasmuch as there was no objection by the defendant, he granted a specific performance of the agreement, as explained by the parol evidence introduced by the defendant.
(f) Woollam v. Hearn, 7 Ves. 211; Lord Cottenham, C, Squire v. Campbell, 1 Mylne & C. 480; London and Birmingham Railway Co. v. Winter, Craig & Ph. 61; Lord St. Leonards, Warren v. Thunder, 8 Irish Eq. 375. See post, p. and note.
(h) Wiyam, V. C, Clay v. Rufford, 8 Hare, 289; and see s. c. before Stuart, V. C, 19 Eng. L. & Eq. 355; Backhouse v. Mohun, 3 Swanst. 434, n. It has been held, that parol evidence is not admissible, even for the defendant, to alter the written agreement, although it may be received to show an equity dehors the agreement. Davis v. Symonds, 1 Cox C. C. 404. And Lord Brougham, Ch., in a case before him, said: *' It has been argued that, although evidence of matter dehors was not admissible for the purpose of raising an equity, it might be given for the purpose of rebutting an equity, and that, therefore, it was competent for the defendant, in a suit for specific performance, to avail himself of such evidence, though it was not competent to the plaintiff to do so. The distinction was sound within certain limits, and within those limits might be safely adopted. Parol evidence of matter collateral to the agreement might be received; but no evidence of matter dehors was admissible to alter the terms and substance of the contract." Croome v. Lediard, 2 Mylne & K. 260. 261; and in that case both the Master of the Rolls and the Lord Chancellor refused to admit parol evidence to show that two separate contracts for the sale and purchase of distinct parcels of land were not independent, but a single agreement for an exchange. But see the criticism upon this case in 1 Sugd. Vend. & P. c. 3, § 8, pl 27. See Howard v. Rogers, 4 Harris; J. 278. (i) Skinner v. McDonall, 2 De G. & S. 265, is an instance of a somewhat strict application of the rule, that a defendant, in order to obtain the benefit of the statute of frauds, must plead the statute, or else explicitly claim its protection by his answer. As to what does or does not constitute a sufficient pleading of the statute, see also 2 Dan. Ch. Pr. (Boston, 1846), 747-752; Cooth v Jackson, 6 Ves. 17. But the defendant is not in all cases excluded from the defence of the statute of frands by omitting to plead it. "Where a defendant admits the agreement, if he means to rely on the fact of its not being in writing and signed, and so being invalid by reason of the statute, he must say so; otherwise he is taken to mean that the admitted agreement was a written agreement, good under the statute, or else that on some other ground it is binding on him; but where he denies or degree, as has been suggested, on the idea that the requirement of the statute is in fact satisfied when the answer supplies a written memorandum of the contract;(j) or on the ground that it is competent to the defendant to waive a rule of law enacted for his benefit; (k) or on the broad ground that a statute for the prevention of frauds and perjuries has no proper application to a case where the defendant does not say there is any fraud, and where there can be no danger of perjury, because he himself has taken away all necessity of proving the contract by his own admission of it, (l) it is clear that the exception itself is well established, (m)
* But the reasons, excepting only that of waiver, would apply as well where the answer does in fact state or confess all the facts of the plaintiffs case, but denies that there was a contract in writing, and rests this defence on the statute of frauds. And there was a time when the courts of equity would disregard the statute in such cases and grant relief, (n) But this brings up the frequently occurring, exceedingly important, and equally difficult question, What are the limits of the obligation imposed upon equity by its own rule, of following the law? (o) For it is perfectly obvious that there can be here nothing else than obedience to the law, or direct violation of it. The law says, in perfectly explicit terms, that a certain contract shall have no force in law or in equity. A party sued in equity comes into court and does not admit the agreement, the bar-den of proof is altogether on the plaintiff, who must then prove a valid agreement capable of being enforced." Lord Cran-worth, Ch., Ridgway v. Wharton, 3 De G., M. & G. 689. And, in a subsequent part of his lordship's judgment, he distinguished the case of a defence taken under the statute of frauds from the defence of the statute of limitations, and observed that the two cases were entirely dissimilar, and that the one statute affords no illustration towards the interpretation of the other. 3 De G., M. & G. 691, 692. See also Ontario Bank v. Root, 3 Paige, 478; Small v Owings, 1 Md. Ch. Dec. 366 , Givens v. Calder, 2 Desaus. 187.
 
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