Invalidity Defenses

Common situations.

• A software patent is asserted, and the defendant believes it claims only an abstract idea.
• The defendant finds an older product or publication that looks like the claimed invention.
• The patent owner sold or offered the invention more than a year before filing.
• A claim term is so vague that its scope cannot be determined.

Patent eligibility (§ 101).

Claims directed to an abstract idea, law of nature, or natural phenomenon are invalid unless they add an inventive concept (Alice Corp. v. CLS Bank Int'l, 573 U.S. 208 (2014)). Eligibility is the most common ground for an early motion to dismiss in software cases.

• Claims that improve how a computer itself works can pass the first step (Enfish, LLC v. Microsoft Corp., 822 F.3d 1327 (Fed. Cir. 2016)).
• Whether claim elements were well understood, routine, and conventional is a question of fact. If the complaint or specification plausibly raises a factual dispute, early dismissal may be denied (Berkheimer v. HP Inc., 881 F.3d 1360 (Fed. Cir. 2018)).
• Applying generic machine learning to a new data environment is not eligible (Recentive Analytics, Inc. v. Fox Corp., No. 2023-2437 (Fed. Cir. Apr. 18, 2025)). The Patent Office, by contrast, treats claims that improve how a machine learning model itself works as eligible (Ex parte Desjardins, Appeal No. 2024-000567 (PTAB Appeals Review Panel Sept. 26, 2025) (precedential)). Board decisions do not bind courts.

Novelty (§ 102).

A claim is anticipated if a single prior art reference discloses every element, arranged as in the claim. Which version of § 102 applies depends on the claim's effective filing date.

• First-inventor-to-file (AIA). For claims with an effective filing date on or after March 16, 2013, prior art includes anything patented, described in a printed publication, in public use, on sale, or otherwise available to the public before that date (§ 102(a)(1)), and earlier-filed U.S. patents and applications of others (§ 102(a)(2)). An inventor's own disclosure within one year before filing is excepted (§ 102(b)(1)).
• First-to-invent (pre-AIA). Older patents are judged under the prior § 102, which looks to the date of invention and a one-year statutory bar. Some of these patents remain in force and in litigation.

The on-sale and public-use bars.

A sale or offer to sell more than one year before filing invalidates the claims if the invention was ready for patenting at the time (Pfaff v. Wells Elecs., Inc., 525 U.S. 55 (1998)). Under the AIA, a sale counts even if its terms were confidential (Helsinn Healthcare S.A. v. Teva Pharms. USA, Inc., 586 U.S. 123 (2019)).

A patent owner's own secret commercial use of a process, by selling products made with it more than a year before filing, also bars a patent on the process. The AIA did not change that rule (Celanese Int'l Corp. v. Int'l Trade Comm'n, No. 2022-1827 (Fed. Cir. Aug. 12, 2024), cert. denied (U.S. Apr. 28, 2025)). Companies that keep a process as a trade secret and later try to patent it face this bar. See Patent, Trade Secret, or Both?

Obviousness (§ 103).

A claim is invalid if the differences between it and the prior art would have been obvious to a person of ordinary skill before the effective filing date. The court weighs the Graham factors: the scope and content of the prior art, the differences, the level of skill, and objective indicia such as commercial success, long-felt need, failure of others, and copying (Graham v. John Deere Co., 383 U.S. 1 (1966)). The inquiry is flexible; a combination of familiar elements by known methods is likely obvious if it does no more than yield predictable results (KSR Int'l Co. v. Teleflex Inc., 550 U.S. 398 (2007)).

For design patents, the Federal Circuit dropped its stricter test in 2024 and now applies the same Graham framework (LKQ Corp. v. GM Global Tech. Operations LLC, 102 F.4th 1280 (Fed. Cir. 2024) (en banc)).

Written description and enablement (§ 112(a)).

• Written description. The specification must show that the inventor possessed the full scope of what is claimed (Ariad Pharms., Inc. v. Eli Lilly & Co., 598 F.3d 1336 (Fed. Cir. 2010) (en banc)).
• Enablement. The specification must teach skilled workers to make and use the full scope of the claimed invention without undue experimentation. Broad functional claims to a whole class are vulnerable (Amgen Inc. v. Sanofi, 598 U.S. 594 (2023)).

Indefiniteness (§ 112(b)).

A claim is invalid if, read in light of the specification and prosecution history, it fails to tell skilled workers the scope of the invention with reasonable certainty (Nautilus, Inc. v. Biosig Instruments, Inc., 572 U.S. 898 (2014)). Claims that use generic words such as "module" or "means" in place of structure may be treated as means-plus-function claims, and are indefinite if the specification discloses no corresponding structure, such as an algorithm for a software function (Williamson v. Citrix Online, LLC, 792 F.3d 1339 (Fed. Cir. 2015) (en banc in relevant part)). Indefiniteness is often decided at claim construction.

Obviousness-type double patenting.

This judge-made doctrine prevents an owner from extending its exclusivity with a second patent claiming an obvious variant of its first. A patent whose term was extended for Patent Office delay can be invalid over a related patent that expires earlier, unless a terminal disclaimer was filed (In re Cellect, LLC, 81 F.4th 1216 (Fed. Cir. 2023)). A first-filed, first-issued parent patent, however, cannot be invalidated by its own later-filed child (Allergan USA, Inc. v. MSN Labs. Private Ltd., No. 2024-1061 (Fed. Cir. Aug. 13, 2024)).

Where invalidity is decided.

See Burdens and Standards of Proof and PTAB Proceedings and Parallel Litigation.

Texas notes.

• Judges in the Eastern and Western Districts of Texas differ in how willing they are to decide § 101 motions before claim construction. Some defer them; others rule on the pleadings.
• The local patent rules in both districts require early invalidity contentions that chart each prior art reference against the asserted claims. A defense not disclosed in contentions may be excluded. See Local Patent Rules.

Sources.

• 35 U.S.C. §§ 101, 102, 103, 112, 282, 311(b), 321(b).
• Leahy-Smith America Invents Act, Pub. L. No. 112-29, § 3(n)(1), 125 Stat. 284, 293 (2011) (effective date of first-inventor-to-file).
• Alice Corp. v. CLS Bank Int'l, 573 U.S. 208 (2014).
• Enfish, LLC v. Microsoft Corp., 822 F.3d 1327 (Fed. Cir. 2016).
• Berkheimer v. HP Inc., 881 F.3d 1360 (Fed. Cir. 2018).
• Recentive Analytics, Inc. v. Fox Corp., No. 2023-2437 (Fed. Cir. Apr. 18, 2025).
• Ex parte Desjardins, Appeal No. 2024-000567 (PTAB ARP Sept. 26, 2025) (designated precedential Nov. 4, 2025).
• Pfaff v. Wells Elecs., Inc., 525 U.S. 55 (1998).
• Helsinn Healthcare S.A. v. Teva Pharms. USA, Inc., 586 U.S. 123 (2019).
• Celanese Int'l Corp. v. Int'l Trade Comm'n, No. 2022-1827 (Fed. Cir. Aug. 12, 2024), cert. denied, No. 24-635 (U.S. Apr. 28, 2025).
• Graham v. John Deere Co., 383 U.S. 1 (1966).
• KSR Int'l Co. v. Teleflex Inc., 550 U.S. 398 (2007).
• LKQ Corp. v. GM Global Tech. Operations LLC, 102 F.4th 1280 (Fed. Cir. 2024) (en banc).
• Ariad Pharms., Inc. v. Eli Lilly & Co., 598 F.3d 1336 (Fed. Cir. 2010) (en banc).
• Amgen Inc. v. Sanofi, 598 U.S. 594 (2023).
• Nautilus, Inc. v. Biosig Instruments, Inc., 572 U.S. 898 (2014).
• Williamson v. Citrix Online, LLC, 792 F.3d 1339 (Fed. Cir. 2015).
• In re Cellect, LLC, 81 F.4th 1216 (Fed. Cir. 2023).
• Allergan USA, Inc. v. MSN Labs. Private Ltd., No. 2024-1061 (Fed. Cir. Aug. 13, 2024).

This guide is general information, not legal advice. Law checked through October 20, 2026. See the Disclaimer.