This section is from the book "The Law Of Contracts", by William Herbert Page. Also available from Amazon: Commercial Contracts: A Practical Guide to Deals, Contracts, Agreements and Promises.
Whatever the relation of the mistake to the contract, if it concerns a matter which is not material thereto, no relief is given on the ground of mistake.1 In order to render a contract void, the mistake as to its terms must be material.2 To render the contract void the mistake must be so material that the contract would not have been made if the truth had been known.3 If A intends to sign a note as surety for B and intends the note to be payable to X, A is not discharged from liability by the fact that the note is by mistake made payable to B, if such note is, in fact, endorsed to X in accordance with the original intention of the parties.4 One who intends to execute a promise to pay money in the future can not avoid the transaction because the instrument is a check instead of a note, although the promisor believed that the instrument was a note.5 A mistake as to the amount of a note, assumed as part of the purchase price of stock, does not make the contract void, if the amount is less than the party assuming it agreed to pay.6
The mistake concerning the subject-matter renders the contract invalid only if it is one which can fairly be regarded as material7 If the boundaries of a tract conveyed are known, the general rule is that a slightly erroneous estimate of its area is not such mistake as to call for rescission.8
The non-existence of a part of the subject-matter which is regarded by the parties as immaterial can not affect the validity of the contract.9 If A and B exchange lands and it is understood that one of the tracts thus exchanged has no value substantially and the owner thereof knows nothing whatever about it, the fact that no such tract exists is not material and is not ground for rescission in equity.10 A contract is not rendered invalid by ignorance of the fact that a contract for a small part of the intended excavation had already been let.11 A compromise will not be disturbed because of the fact that by mistake a payment has been credited twice if, even after correcting such mistake, the balance due is equal to the amount claimed.12 If the parties have agreed upon a certain tract of land which is made up of several parcels, the fact that by mistake one of the parcels is described twice, does not render the contract of sale invalid if the price was not affected thereby.13 A slight mistake as to area,14 or boundary line,15 is held not to justify rescission. So a mistake as to one boundary line, the vendee believing that the tract in question included an abandoned shaft once used for mining gold, is not ground for relief where the evidence shows that the land was sold for mining purposes and that the existence of such shaft would not in any way increase its value, and did not in any way affect vendee.16 On the other hand, a serious discrepancy in area, as where a tract of one hundred thirty-five acres was thought to contain two hundred acres,17 or a tract of two hundred fifty acres was thought to contain only one hundred ninety-eight,18 may be ground for rescission.
1 United States. Grymes v. Sanders, 93 U. S. 55, 23 L. ed. 798.
Arkansas. Carwell v. Dennis, 101 Ark. 603, 143 S. W. 135.
Iowa. Wilson v. Gunning, 80 la. 331, 45 N. W. 920.
Kentucky. Mattingly v. Stone (Ky.), 12 S. W. 467, 12 Ky. Law Rep. 72.
Missouri. Lyman v. Campbell, 34 Mo. App. 213; Wood v. Evans, 43 Mo. App. 230.
Nebraska. Lamoreaux v. Phelan, 89 Neb. 47, 130 N. W. 988.
New Jersey. Nicholson v. Janeway, 16 N. J. Eq. 285.
New York. Southwick v. Bank, 84 N. Y. 420.
Tennessee. Trigg v. Read, 24 Tenn. (5 Humph.), 529, 42 Am. Dec. 447.
Virginia. Rogers v. Pattie, 96 Va. 498, 31 S. E. 807.
2 Bassett v. O'Neil Coke & Coal Co., 140 Ky. 346, 131 S. W. 25; Columbian Conservatory of Music v. Dickenson; 158 N. Car. 207, 73 S. E. 990
3 Lamoreaux v. Phelan, 89 Neb. 47, 130 N. W. 988; McCrea v. Hinkson, 65 Or. 132. 131 Ac. 1025.
4 Bassett v. O'Neil Coal & Coke Co., 140 Ky. 346, 131 S. W. 25
5 Columbian Conservatory of Music 990.
6 Kaufman v. Bank, 31 Neb. 661, 48 N. W. 738.
7 Murray v. Paquin, 173 Fed. 319.
8 Wier v. Johns, 14 Colo. 493, 24 Ac. 202; Wilson v. Gunning, 80 Ta. 331, 45 N. W. 920; Rodgers v. Olshoffsky, 110 Pa. St. 147, 2 Atl. 44; Conta v. Corgiat, 74 Wash. 28, 132 Ac. 746.
9 Carwell v. Dennis, 101 Ark. 603, 143 S. W. 135.
A mistake as to the identity of the entire tract renders the contract void, even if the tract which is actually sold is as valuable as the one which, by mistake, was pointed out to the vendee.19 The identity of the adversary party seems to be regarded as necessarily material.20