
90 U.S. 492 (____)
23 Wall. 492
MORAN ET AL.
v.
PRATHER.
Supreme Court of United States.

*498 Mr. Bentinck Egan, for the plaintiff in error.
Mr. Montgomery Blair, contra.
*499 Mr. Justice CLIFFORD delivered the opinion of the court.
The errors assigned are: (1.) That the Circuit Court erred in excluding the evidence offered by the defendants that the words "steamboat debts" mean such debts as constitute a lien or privilege on the steamboat for necessary supplies, materials, repairs, and wages; that they do not include debts which cannot be enforced against the steamboat by any of the conservatory laws of the State. (2.) That the court erred in admitting the testimony offered by the plaintiff that the steamboat, at the time of the sale, was a very valuable vessel, that the interest of the plaintiff was worth much more than the amount for which it was sold, and that it was understood at the time of the sale that the purchaser should assume and protect the plaintiff from all existing debts of the steamboat, and that the purchaser should give a bond to that effect. (3.) That the instructions given to the jury were erroneous. (4.) That the court erred in refusing to instruct the jury as requested by the defendants.
1. Cases arise undoubtedly in which the testimony of expert witnesses is admissible to explain terms of art and technical words or phrases, and it may be admitted that a written instrument may be so interspersed with such technical terms that it would be error in the court to exclude the testimony of persons skilled in such matters, if duly offered by the proper party in the litigation.[*]
Terms of art, in the absence of parol testimony, must be understood in their primary sense, unless the context evidently shows that they were used in the particular case in some other and peculiar sense, in which case the testimony of persons skilled in the art or science may be admitted to aid the court in ascertaining the true intent and meaning of that part of the instrument, but the words of the instrument which have reference to the usual transactions of life must be interpreted according to their plain, ordinary, and popular meaning; and the rule is that parol *500 evidence is not admissible to contradict or vary such an instrument.[*]
Difficulty will sometimes arise in determining whether the particular term or phrase in question is used in a technical or in a popular sense, but the court is of the opinion that no such difficulty is presented in this investigation. Instead of that it is quite clear that neither the words of the guarantee given by the plaintiff to his vendor when he made his second purchase nor the words used in the guarantee given by the defendants to the plaintiff are either doubtful or ambiguous, nor are the words of either of those contracts of a character to afford the slightest support to the proposition that parol testimony of any kind would be admissible to contradict, vary, or to unfold or expound their ordinary signification and meaning.
By the allegation of the petition it appears that the plaintiff when he made his second purchase bound and obligated himself to hold his vendor free and harmless of all debts of the steamboat and owners, existing against the steamboat at the date of the sale, and to reimburse him for any and all debts then existing that he should be compelled to pay on account of his having been an owner of the same. Language equally clear, comprehensive, and decisive is employed in the guarantee given by the defendants to the plaintiff when he transferred his entire interest to the person in whose behalf the defendants executed the guarantee which is the foundation of the present suit. Subject to the exception before stated they bound themselves and their heirs in solido to defend the plaintiff, and save him free and harmless of any and all claims and demands that may arise or be brought against the steamboat, which language is neither technical nor ambiguous, and it certainly falls within that class of expressions which by all the authorities must be interpreted according to their plain, ordinary, and popular meaning.[]
*501 Where the words of any written instrument are free from ambiguity in themselves, and where the external circumstances do not create any doubt or difficulty as to the proper application of the words to the claimants under the instrument, or the subject-matter to which the instrument relates, such an instrument, said Tindal, C.J., is always to be construed according to the strict, plain, common meaning of the words themselves, and that in such cases evidence dehors the instrument for the purpose of explaining it, according to the surmised or alleged invention of the parties to the instrument, is utterly inadmissible.[*]
All the facts and circumstances may be taken into consideration, if the language be doubtful, to enable the court to arrive at the real intention of the parties, and to make a correct application of the words of the contract to the subject-matter and the objects professed to be described, for the law concedes to the court the same light and information that the parties enjoyed, so far as the same can be collected from the language employed, the subject-matter, and the surrounding facts and circumstances.[]
Ambiguous words or phrases may be reasonably construed to effect the intention of the parties, but the province of construction, except when technical terms are employed, can never extend beyond the language employed, the subject-matter, and the surrounding circumstances.[]
Apply that rule to the case and it is clear that the evidence offered by the defendants was properly excluded, and that the exception under consideration must be overruled.
2. Evidence was introduced by the plaintiff at the trial that his interest in the steamboat was worth much more than the amount for which the same was sold, and that it was understood at the time of the sale that the purchaser should assume and protect the plaintiff from all existing debts of the vessel and give a bond to that effect. Exception *502 was taken by the defendants to the ruling of the court in admitting that testimony, which ruling is the foundation of the next assignment of errors.
Parol evidence is certainly not admissible to contradict, vary, or control a written contract, but the evidence in question in this case is not subject to any such objection, whether applied to the guarantee given by the plaintiff to his vendor or to the bill of sale given to the plaintiff by the purchaser of his interest in the steamboat. Much less was paid for that interest than its market value, the evidence of which was properly admissible as showing the surrounding circumstances at the time the bill of sale was executed, and also to show the circumstances which induced the purchaser to give the guarantee executed by the defendants.
3. Specifications of error under the third assignment involve the same question, or some phase of the same question, as that contained in one or the other of the two preceding assignments.
The defendants insisted in the court below, and still insist, that the phrase "steamboat debts" is a technical phrase, and that it did not include any debts except such as constitute a lien on the steamboat. Attempt is made to set up that theory by exceptions to the charge, as well as by exceptions to the rulings of the court, but several answers may be given to the theory, either of which is sufficient to show that the exceptions are not well founded: (1.) That the language of the guarantee is not correctly reproduced. (2.) That the phrase referred to is not a technical phrase within the meaning of the rules of evidence applicable in such cases. (3.) That by the true construction of the guarantee it includes all existing debts contracted for repairs, supplies, and running expenses for and on account of the steamboat, for which the plaintiff, as owner, was liable at the time of the sale and purchase.
Evidently the object of the agreement of guarantee was to secure the plaintiff against all liability arising from his part-ownership of the steamboat. It was his liability and not that of the steamboat which was to be protected from "all *503 claims and demands that may arise or be brought against the steamboat."
4. Certain requests for instruction were also presented by the defendants which were refused by the presiding justice, and the court here is of the opinion that all of them were properly refused.
Partnership may be proved by parol as well as by written evidence, which is sufficient to show that the ruling of the circuit judge in refusing the first request is correct, and enough has already been remarked in response to the first exception to show that the other requests for instruction were properly refused, for the plain reason that every one of them sets up an erroneous theory of the guarantee which is the foundation of the suit.
Evidence of usage was offered by the defendants to limit the legitimate scope and operation of the instrument of guarantee, but it was excluded by the court for reasons so manifestly proper that no argument is necessary to vindicate the action of the court.[*]
Usage cannot be incorporated into a contract which is inconsistent with the terms of the contract; or, in other words, where the terms of a contract are plain usage cannot be permitted to affect materially the construction to be placed upon it, but when the terms are ambiguous usage may influence the judgment of the court in ascertaining what the parties meant when they employed those terms.
Apply those rules to the case and it is clear that the theory of the controversy assumed by the circuit judge in all his rulings and in the instructions which he gave to the jury is correct. Conclusive proof of that proposition is found in the language of the guarantee, by which the defendants covenanted to save the plaintiff free and harmless of any and all claims and demands that may arise or be brought against the steamboat, except such as were relinquished by the instrument in writing executed on the same day.
JUDGMENT AFFIRMED.
NOTES
[*]  Seymour v. Osborne, 11 Wallace, 546.
[*]  Greenleaf on Evidence, 12th edition, § 285; 1 Taylor on Evidence, 6th edition, § 367.
[]  2 Taylor on Evidence, 6th edition, § 1034; Robertson v. French, 4 East, 135.
[*]  Shore v. Wilson, 9 Clark & Finelly, 565; Mallan v. May, 13 Meeson & Welsby, 517.
[]  Addison on Contracts, 6th edition, 918.
[]  Nash v. Towne, 5 Wallace, 689.
[*]  Thompson v. Riggs, 5 Wallace, 679; Bliven v. New England Screw Company, 23 Howard, 431; Addison on Contracts, 6th edition, 935.
