Where the declaration purports to set out an instrument according to its substance and effect, it is ordinarily sufficient, if the instrument proved, and the one alleged, correspond in all essential particulars. Let us inquire if the writing declared on, and that given in evidence, thus harmonize with each other.
The plaintiff alleges that on the 9th of July, 18.38, he entered into a written contract with the defendant and others, to teach an English school for that year. The declaration avers the expiration of the term of the plaintiff’s engagement to be the end of that year, and that the defendant then agreed to pay him his entire yearly compensation. The contract produced and given in evidence is, to teach an English school “ for one year,” without designating from what time the year begins. In the absence of an express stipulation on this point, it is clear that the term of the plaintiff’s employment began to run from the time when the contract was entered into. The defendant, did not agree to pay the plaintiff for teaching a school “ for the year;” had such been the language used, then the engagement would have been limited to the current year. But he undertakes, with the other contracting parties, to pay him, “for one year,” which, according to all rules of interpretation, commences on the day intimated, and ends on the 9th July, 1839. It will therefore follow, that the writing given in evidence by the plaintiff, was improperly admitted by the Circuit Judge, as being substantially variant from that declared one. Ferguson v. Harwood, 7 Cranch’s Rep. 408; Silver v. Kendrick, 2 N. Hamp. Rep. 160; Query v. Brindlinger, Litt. Select Cases, 87; Lawrence v. Barker, 5 Wend. Rep. 301; Taylor v. Hickman, Litt. Select Cases, 434; Willoughby v. Raymond, 4 Conn. Rep. 130; Curley v. Dean, 4 Conn. Rep. 259; Smith v. Barker, 3 Day’s Rep. 312; Crawford, et al. v. Monell, 8 Johns. Rep. 253; Colt. v. Root, 17 Mass. Rep. 229; Bulkley v. Landon, 2 Conn. *185Rep. 404; King v. Pippett, 1 T. Rep. 240; Bristow v. Wright, Doug. Rep. 665; Gwinnett v. Phillips, 3 T. Rep. 646.
Parol evidence has been admitted to give direction to and apply a written instrument, but it is not admissible to add to, or vary its terms. 3 Phil. Evi. 1466, et post, and cases cited.— The contract adduced at the trial, was sufficiently clear without extrensic aid, to ascertain the rights and liabilities of the parties; and the admission of parol evidence, so as to give to the writing a retrospective operation, materially changed its import. Its effect was to add to, and even to contradict the instrument, and according to the rule stated, its introduction under the sanction of the Court, was palpably erroneous.
If all the employers of the defendant in error, had taken their children from his school, he would have been left without scho-^ lars, and of necessity, must have ceased teaching. Those who did so, indicated that they were willing to dispense with his services, as much as if they had so informed him ; and to excuse the non-performance of his contract, it was only necessary to obtain the consent-of those who were willing to continue him . as a teacher. This conclusion, we think too clear to require argument to prove it. If the scholars were taken from the school in consequence of sickness, or other cause, of a temporary nature, and under circumstances not to show, that their withdrawal was intended to continue for the entire term of the employment; then the defendant would not have been excused without the consent of all his employers, unless he could prove without reference to the appearance of the act, that the intention was to dispense with his services.
In the case before us, the plaintiff alleges in the declaration, the performance of his contract, and seeks to recover the entire sum agreed to be paid him in consideration thereof; while he attempts to show an excuse for its non-performance, so as to entitle himself to recover for the period during which he was actually employed.
It is an acknowledged rule in the law of pleading and evidence, that the allegata and probata must correspond. Under the influence of this rule, it has been held, that where an averment of performance is necessary, the plaintiff must not only aver, that he was ready, and did all he could to perform his undertaking; and if he relies upon an excuse for a failure *186he must allege the particular circumstances» which occasioned a non-performance. Coppice v. Hurnard, 2 Saund. Rep. 129; 2 East Rep. 145 ; 1 H. Bla. Rep. 287; 4 East Rep. 147. But if the defendant has prevented a performance, under such circumstances as would entitle the plaintiff to recover as much as ho would, had the contract been entirely executed on his part, then perhaps it may be unnecessary to allege in the pleading any matter of excuse. 5 B. &. C. Rep. 638; 2 D. & R. Rep. 347. See further on this point, Poague v. Richardson, Litt. Select Cases, 134; Holt v. Crume, Litt. Select Cases, 499.
This view disposes of the questions of law arising upon the record. We will not inquire whether the defendant in error may not recover for all the time he was engaged in teaching, or what form of declaration is necessary to let in his proof. These are questions which he must determine for himself, at least for the present.
The judgment of the Circuit Courtis reversed, and the cause remanded.