What is Non Est Factum?

Legal Definition
Non est factum (Latin for "it is not [my] deed") is a defence in contract law that allows a signing party to escape performance of an agreement "which is fundamentally different from what he or she intended to execute or sign." A claim of non est factum means that the signature on the contract was signed by mistake, without knowledge of its meaning. A successful plea would make the contract void ab initio.

According to Saunders v Anglia Building Society [1971], applied in Petelin v Cullen [1975], the strict requirements necessary for a successful plea can are generally that:

  1. The person pleading non est factum must belong to "class of persons, who through no fault of their own, are unable to have any understanding of the purpose of the particular document because of blindness, illiteracy or some other disability." The disability must be one requiring the reliance on others for advice as to what they are signing.
  2. The "signatory must have made a fundamental mistake as to the nature of the contents of the document being signed," including its practical effects.
  3. The document must have been radically different from one intended to be signed.

Non est factum is difficult to claim as it does not allow for negligence on the part of the signatory, i.e. failure to read a contract before signing it, or carelessness, will not allow for non est factum. Furthermore, the Court has noted that there is a heavy onus that must be discharged to establish this defence as it as an "exceptional defence."
-- Wikipedia
Legal Definition
Pleading. The general issue in debt on bond or other specialty, and is, in form, as follows: I " And the said C D, by E F, his attorney, conies and defends the wrong and injury, when, &c., and says, that the said supposed writing obligatory, (or 'indenture,' or 'articles of agreement,' according to the subject of the action,) is not his deed. And of this he puts himself upon the country." 6 Rand. Rep. 86; 1 Litt. R. 158.

2. Though non est factum is, in most cases, the general issue in debt on specialty, yet, when the deed is only inducement to the action, the general issue is nil debet. Steph. Pl. 174, n.

3. In covenant the general issue is non est factum; and its form is similar to that in debt on a specialty. Id. 174. It is, however, said, that in covenant there is, strictly speaking, no general issue, as the plea of non est factum only puts the deed in issue, as in debt on a specialty, and not the breach of covenant or any other matter of defence. 1 Chit. PI. 482. See generally, 1 Harring. R. 230; 6 Munf. R. 462; Minor, R. 103; 1 Harr. & Gill, 324; 13 John. R, 430; 12 John. R. 337; 2 N. H. Rep. 74; 4 Wend. R. 519; 2 N. & M. 492. See Issint; Special non est factum.
-- Bouviers Law Dictionary
Legal Definition
Lat A plea by way of traverse, which occurs in debt on bond or other specialty, and also in covenant It denies that the deed mentioned in the declaration is the defendant's deed. Under this, the defendant may contend at the trial that the deed was never executed in point of fact; but he cannot deny its validity in point of law. Wharton; Haggart v. Morgan, 5 N. Y. 422, 55 Am. Dee. 350; Evans v. Southern Turnpike Co.., 18 Ind. 101. The plea of non est factum is a denial of the execution of the instrument sued upon, and applies to notes or other instruments, as well as deeds, and applies only when the execution of the instrument is alleged to be the act of the party filing the plea, or adopted by him. Code Ga. 1882, ยง 3472. See Special non est factum.
-- Black's Law Dictionary