It is very common for parties to offer evidence external to the contract, in aid of the interpretation of its language. The * general rule is, that such evidence cannot be admitted to contradict or vary the terms of a valid written contract; or, as the rule is expressed by writers on the Scotch law, "writing cannot be cut down or taken away by the testimony of witnesses." (z) There are many reasons for this rule. One is, the general preference of the law for written evidence over unwritten; or, in other words, for the more definite and certain evidence over that which is less so; a preference which not only makes written evidence better than unwritten, but classifies that which is written. For if a negotiation be conducted in writing, and even if there be a distinct proposition in a letter, and a distinct assent, making a contract; and then the parties reduce this contract to writing, and both execute the instrument, this to receive from the landlord or incoming tenant a reasonable allowance for seeds and labor bestowed on the arable land in the last year of the tenancy, and is bound to leave the manure for the landlord, if he will purchase it, - is not excluded by a stipulation in the lease under which he holds, that he will consume three-fourths of the hay and straw on the farm, and spread the manure arising therefrom, and leave such of it as shall not be so spread on the land for the use of the landlord, on receiving a reasonable price for it Hutton v. Warren, 1M.& W. 466. See also Senior v. Armytage, Holt, instrument controls the letters, and they are not permitted to vary the force and effect of the instrument, although they may sometimes be of use in explaining its terms. Another is, the same desire to prevent fraud which gave rise to the statute of frauds; for as that statute requires that certain contracts shall be in writing, so this rule refuses to permit contracts which are in writing to be controlled by merely oral evidence. But the principal cause alleged in the books and cases is, that when parties, after whatever conversation or preparation, at last reduce their agreement to writing, this may be looked upon as the final consummation of their negotiation, and the exact expression of their purpose. And all of their earlier agreement, though apparently made while it all lay in conversation, which is not now incorporated into their written contract, may be considered as intentionally rejected. (a) The parties write the contract when they are ready to do so, for * the very purpose of including all that they have finally agreed upon, and excluding everything else, and make this certain and permanent. And if every written contract were held subject to enlargement, or other alteration, according to the testimony which might be offered on one side or the other as to previous intention, or collateral facts, it would obviously be of no use to reduce a contract to writing, or to attempt to give it certainty and fixedness in any way. (b)

N. P. 107; Syers v. Jonas) 2 Exch. 111. If the legislature has given to a particular word denoting quantity a definite meaning, no evidence of usage can be given to show that it is used in a different sense. Smith v. Wilson, 8 B. & Ad. 728. See Helm v. Bryant, 11 B. Mon. 64; and note to Wigglesworth v. Dallison, 1 Smith's Lead. Cas. 308, b.

(y) Boldero v. East India Co. 26 Beav. 316.

(z) Tait on Ev. 826. See further Herring v. Boston Iron Co. 1 Gray, 184; Renard v. Sampson, 2 Kern. 661.

1 Local usage cannot change a warehouse receipt from a bailment to a sale. Ledyard v. Hibbard, 48 Mich. 421.

It is nevertheless certain, that some evidence from without must be admissible in the explanation or interpretation of every contract. If the agreement be, that one party shall convey to the other, for a certain price, a certain parcel of land, it is only by extrinsic evidence that the persons can be identified who claim or are alleged to be parties, and that the parcel of land can be ascertained. It may be described by bounds, but the question then comes, where are the streets, or roads, or neighbors, or monuments referred to in the description; and it may sometimes happen that much evidence is necessary to identify these persons or things. Hence, we may say, as the general rule, that as to the parties or the subject-matter of a contract, extrinsic evidence may and must be received and used to make them certain, if necessary for that purpose. (c)1 But as to the terms, conditions, and limitations of the agreement, the written contract must speak exclusively for itself. Hence, too, a false description of person or thing has no effect in defeating a contract, if the error can be distinctly shown and perfectly corrected, by other matter in the instrument. (d)

(a) Preston v. Merceau, 2 W. Bl. 1249; Harnor v. Groves, 16 C. B. 667, 29 Eng. L. & Eq. 220; Carter v. Hamilton, 11 Barb. 147; Troy Iron and Nail Factory v. Corning, 1 Blatchf. G. C. 467; Meres v. Ansel, 3 Wilson, 276; Hakes v. Hotch-kiss, 23 Vt. 231; Vermont Central R. R. Co. v. Estate of Hills, id. 681. "Where the whole matter passes in parol, all that passes may sometimes be taken together as forming parcel of the contract, though not always, because matter talked of at the commencement of a bargain may be excluded by the language used at its termination. But if the contract be in the end reduced into writing, nothing which is not found in the writing can be considered as a part of the contract." Per Abbott, C. J., in Kain v. Old, 2 B. & C. 634. See also Vandervort v. Smith, 2 Caines, 155; Mumford v. M'Pherson, 1 Johns. 414; Pickering v. Dowson, 4 Taunt. 786.

(b) "It would be inconvenient that matters in writing, made by advice and on consideration, and which finally import the certain truth of the agreement of the parties, should be controlled by averment of the parties, to be proved by the uncertain testimony of slippery memory." Countess of Rutland's case, 6 Rep. 26 a; Carter v. Hamilton, 11 Barb. 147; Rogers v. Atkinson, 1 Ga. 12; Wynn v. Cox. 5 id. 373.