35 U.S.C. § 112: The specification shall contain a written description of the invention, and of the manner and process of making and using it, in such full, clear, concise, and exact terms as to enable any person skilled in the art to which it pertains, or with which it is most nearly connected, to make and use the same, and shall set forth the best mode contemplated by the inventor of carrying out his invention.

In regard to §112, the CAFC noted -

In 1967, this court’s predecessor inaugurated use of § 112 to prevent the addition of new matter to claims. In re Ruschig, 379 F.2d 990 (CCPA 1967). Thus, in a recent application of the written description doctrine, this court noted: “The purpose of the written description requirement is to prevent an applicant from later asserting that he invented that which he did not; the applicant for a patent is therefore required ‘to recount his invention in such detail that his future claims can be determined to be encompassed within his original creation.’” Amgen Inc. v. Hoechst Marion Roussel Inc., 314 F.3d 1313, 1330 (Fed. Cir. 2003) (citing Vas-Cath Inc. v. Mahurkar, 935 F.2d 1555, 1561 (Fed. Cir. 1991)).

Compliance with § 112 requires sufficient information in the specification to show that the inventor possessed the invention at the time of that original disclosure. See Vas-Cath, 935 F.2d at 1561 (“Adequate description of the invention guards against the inventor’s overreaching by insisting that he recount his invention in such detail that his future claims can be determined to be encompassed within his original creation.”). The possession test requires assessment from the viewpoint of one of skill in the art. Id. at 1563-64 (“[T]he applicant must . . . convey with reasonable clarity to those skilled in the art that, as of the filing date sought, he or she was in possession of the invention.” (emphasis in original)); Union Oil Co. of Cal. v. Atl. Richfield Co., 208 F.3d 989, 997 (Fed. Cir. 2000) (“The written description requirement does not require the applicant ‘to describe exactly the subject matter claimed, [instead] the description must clearly allow persons of ordinary skill in the art to recognize that [the inventor] invented what is claimed.’” (citation omitted)).

The CAFC affirmed the district court's summary judgment that the written description of the '046 sufficiently supported claim limitations of the contested terms  “adhering material” and “sole means,” id., both of which were added by amendment during prosecution.

An unusual instance of assignor estoppel arose, where the inventor & assignor, Hartley Young, was barred from testifying against his own patent.

Invoking the doctrine of assignor estoppel, the district court excluded Mr. Young’s testimony. “Assignor estoppel is an equitable doctrine that prevents one who has assigned the rights to a patent (or patent application) from later contending that what was assigned is a nullity.” Diamond Scientific Co. v. Ambico, Inc., 848 F.2d 1220, 1224 (Fed. Cir. 1988). Thus, an assignor and parties in privity with the assignor are estopped or barred from asserting invalidity defenses. Id. In this case, the district court invoked that doctrine to bar an assignor from testifying against the validity of its own patent.

Courts frequently mention four justifications for the doctrine of assignor estoppel: “(1) to prevent unfairness and injustice; (2) to prevent one [from] benefiting from his own wrong; (3) [to adopt the] analogy [of]. . . estoppel by deed in real estate; and (4) [to adopt the] analogy to a landlord-tenant relationship.” Id. (quoting Hal Cooper, Estoppel to Challenge Patent Validity: The Case of Private Good Faith vs. Public Policy, 18 Case W. Res. 1122, 1128 (1967)).

This case relies primarily on the “unfairness and injustice” justification. “[A]n assignor should not be permitted to sell something and later assert that what was sold is worthless, all to the detriment of the assignee.” Diamond, 848 F.2d at 1224. “The principle of fair dealing as between assignor and assignee of a patent whereby the assignor will not be allowed to say that what he has sold as a patent was not a patent has been part of the fabric of our law throughout the life of this nation.” Id. (quoting Scott Paper Co. v. Marcalus Mfg. Co., 326 U.S. 249, 260 (Frankfurter, J., dissenting)). Thus, assignor estoppel prevents an assignor from asserting that its own patent, for which it may have received value upon assignment, is invalid and worthless. The district court properly excluded Mr. Young’s testimony on this basis.