Evidence of the custom or usage of a trade, or of a particular locality, is admissible, though it may add a term to a contract, or may attach a special, and sometimes unnatural, meaning to one of the terms expressed.33
As an instance of a usage which annexes a term to a contract, we may cite the warranty of seaworthiness which by custom is always implied in a contract of marine insurance, though not specially mentioned. So, also, in a case of agricultural customs, a usage that the tenant, quitting his farm at Christmas, was entitled to reap grain sown the preceding autumn, was held in England to be annexed to his lease, though the lease was under seal, and was silent on the subject.34 And in a New York case it was held that, where a contract for excavating city lots was silent as to whom the sand and dirt taken out should belong to, a well-known custom by which it belonged to the excavator, and not to the owner of the lots, might be shown as evidence of the contract.36
The principle on which usages are so annexed has been said to rest on the "presumption that in such transactions the parties did not mean to express in writing the whole of the contract by which they intended to be bound, but to contract with reference to those known usages." 36
Proof of custom and usage is also admissible to explain words and phrases in contracts, where they are commercial terms, or otherwise subject to known customs. The principle on which such explanation is admitted has been said to be "that words perfectly unambiguous in their ordinary meaning are used by the contractors in a different sense from that. * * * In such cases the evidence neither adds to, nor qualifies, nor contradicts the written contract; it only ascertains it by expounding the language." 37 As illustrating this rule, in commercial contracts in the case of charter parties in which the days allowed for unloading the ship are to commence "on arrival" at the port of discharge, evidence may be given to show what is commonly understood to be the port; for some ports are of large area, and, by custom "arrival" is understood to mean arriving at a particular spot in the port.38 Another illustration is a case in which a covenant by the lessee of a rabbit warren that he would leave 10,000 rabbits on the warren was explained by evidence of a usage of the locality to mean 12,000, because 1,000 meant 1,200.39
33 Wilcox v. Wood, 9 Wend. (N. Y.) 346; Rindskoff v. Barrett, 14 Iowa, 101; Potter v. Morland, 3 Cush. (Mass.) 384; Sampson v. Gazzan, 6 Port (Ala.) 123, 30 Am. Dec. 578; Thompson v. Brannin, 94 Ky. 490, 21 S. W. 1057; Swift Iron Works v. Dewey, 37 Ohio St. 242; Steamboat Albatross v. Wayne, 16 Ohio, 513; Newhall v. Appleton, 114 N. Y. 140, 21 N. E. 105, 3 L. R. A. 859; Patterson v. Crowther, 70 Md. 124, 16 Atl. 531; Brown Chemical Co. v. Atkinson, 91 N. C. 389; McCullough v. Hellwig, 66 Md. 269, 7 Atl. 455; Breen v. Moran, 51 Minn. 525, 53 N. W. 755; Donovan v. Standard Oil Co., 155 N. Y. 112, 49 N. E. 678. See "Customs and Usages," Dec. Dig. (Key-No.) § 16; Cent. Dig. §§ 27, 28; "Evidence," Cent. Dig. §§ 1945-1952.
34 Wigglesworth v. Dollison, 1 Smith, Lead. Cas. 594. See "Customs and Usages," Dec. Dig. (Key-No.) § 16; Cent. Dig. §§ 27, 28; "Evidence," Cent. Dig. §§ 191,5-1952.
35 COOPER v. KANE, 19 Wend. (N. Y.) 3S6, 32 Am. Dec. 512, Throckmorton Cas. Contracts, 345. And see Hewitt v. Lumber Co., 77 Wis. 548, 46 N. W. 822. See "Customs and Usages," Dec. Dig. (Key-No.) § 16; Cent. Dig. §§ 27, 28; "Evidence," Cent. Dig. §§ 1945-1952.
35 riutton v. Warren, 1 Mees. & W. 466; Appleman v. Fisher, 34 Md. 540.
Closely connected with this principle is the admissibility of expert testimony to explain terms of art or technical phrases when used in documents.40