What is the defence of non est factum?

The defence of non est factum comes from the Latin phrase “Haec scriptum non est factum meum” which means “this writing is not my deed.” It had its origin in medieval times when the bulk of the population was illiterate. In the course of its development, non est factum was made available to a defendant who could not read, whether owing to illiteracy or blindness so as to enable him to escape liability on proof that the written terms on the document did not correspond with its effect as was explained to him. Thus in Foster v. Mackinnon (1869), L.R. 4 C.P. 704, the court stated as follows: It seems plain on principle and on authority that if a blind man, or a man who cannot read or who for some reason (not implying negligence) forbears to read, has a written contract falsely read over to him, the reader misreading to such a degree that the written contract is of a nature altogether different from the contract pretended to be read from the paper which the blind or illiterate man afterwards signs; then, at least if there be no negligence, the signature so obtained is of no force. And it is invalid not merely on the ground of fraud, where fraud exists, but on the ground that the mind of the signer did not accompany the signature; in other words that he never intended to sign, and therefore in contemplation of law never did sign, the contract to which his name is appended.