What is the law of forgery in common law?

In Jackson v. Weisiger (1841) 41 Ky. 214, a slander action, the court had occasion to comment upon the law of forgery. The plaintiff had prepared a forged letter purporting to be signed by another recommending him as an eminent physician. The letter contained the false assertion that the authors would have been happy to take him on as a partner. The court said: "Interpreting the letter on its face, unaffected by any intrinsic fact, it neither imports a transfer or extinguishment of any right, or an obligation for money or other thing, nor purports to have been even designed as evidence of a partnership, to be used for the fraudulent purpose of depriving [the purported authors] of their property. The letter purports to have been written for the purpose of repelling imputations injurious to [plaintiff], and of commending him to the favorable consideration of [the addressee]; and, as before intimated, it alludes to a subsisting partnership, apparently for the purpose of illustrating the good opinion thus expressed of his merits. [p] The fabrication of such a letter, for such a purpose, though very discreditable, would not have been a technical forgery or other criminal offence [sic] punishable by either the common or statute law of Kentucky." (Id. at p. 215.)