35 U.S.C. · Part II · Chapter 11, Application for patent

35 U.S.C. 112: Specification

In plain English

Section 112 sets the requirements for the specification and the claims. Section 112(a) has three disclosure requirements. The written description must show that the inventor possessed the full scope of what is claimed. The specification must enable a person skilled in the art to make and use the invention without undue experimentation. And it must set out the best mode the inventor contemplated for carrying out the invention.

Section 112(b) requires claims that particularly point out and distinctly claim the invention. In court, a claim is indefinite if, read in light of the specification and prosecution history, it fails to inform skilled artisans about the scope of the invention with reasonable certainty (Nautilus). At the USPTO, examiners ask whether the claim, given its broadest reasonable interpretation, is clear (MPEP 2173).

Sections 112(c) to (e) govern claim form. A dependent claim must refer to an earlier claim and add a further limitation, and it incorporates every limitation of the claim it refers to. A multiple dependent claim refers to more than one earlier claim in the alternative only, and cannot serve as the basis for another multiple dependent claim.

Section 112(f) allows a claim element to be written as a means or step for performing a function. Such an element is not as broad as its words: it covers only the corresponding structure, material or acts described in the specification, and their equivalents. If the specification discloses no corresponding structure (for software, an algorithm), the claim is indefinite.

Annotation by Raj Sutariya, Co-founder, PatentAssist.ai. General information, not legal advice; the statute below governs.

AIA and pre-AIA

The AIA relettered the six unnumbered paragraphs of pre-AIA section 112 as subsections (a) to (f), so “112, first paragraph” is now 112(a) and “112, sixth paragraph” is 112(f). It also provided, in section 282(b)(3)(A), that failure to disclose the best mode can no longer be used to cancel a claim or hold it invalid or unenforceable. The best mode requirement itself remains in section 112(a), and examiners can still raise it.

Text of 35 U.S.C. 112

Current text, quoted from the official United States Code.

(a) In General.— 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 or joint inventor of carrying out the invention.
(b) Conclusion.— The specification shall conclude with one or more claims particularly pointing out and distinctly claiming the subject matter which the inventor or a joint inventor regards as the invention.
(c) Form.— A claim may be written in independent or, if the nature of the case admits, in dependent or multiple dependent form.
(d) Reference in Dependent Forms.— Subject to subsection (e), a claim in dependent form shall contain a reference to a claim previously set forth and then specify a further limitation of the subject matter claimed. A claim in dependent form shall be construed to incorporate by reference all the limitations of the claim to which it refers.
(e) Reference in Multiple Dependent Form.— A claim in multiple dependent form shall contain a reference, in the alternative only, to more than one claim previously set forth and then specify a further limitation of the subject matter claimed. A multiple dependent claim shall not serve as a basis for any other multiple dependent claim. A multiple dependent claim shall be construed to incorporate by reference all the limitations of the particular claim in relation to which it is being considered.
(f) Element in Claim for a Combination.— An element in a claim for a combination may be expressed as a means or step for performing a specified function without the recital of structure, material, or acts in support thereof, and such claim shall be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof.

Key cases

In re Wands, 858 F.2d 731 (Fed. Cir. 1988). Lists the factors for deciding whether experimentation is undue, including the quantity of experimentation, guidance and working examples given, the nature of the invention, the state and predictability of the art, and the breadth of the claims.
Ariad Pharm., Inc. v. Eli Lilly & Co., 598 F.3d 1336 (Fed. Cir. 2010) (en banc). Written description is a requirement separate from enablement. The specification must reasonably convey to skilled artisans that the inventor had possession of the claimed subject matter as of the filing date.
Nautilus, Inc. v. Biosig Instruments, Inc., 572 U.S. 898 (2014). A claim is indefinite if, read in light of the specification and prosecution history, it fails to inform those skilled in the art about the scope of the invention with reasonable certainty.
Williamson v. Citrix Online, LLC, 792 F.3d 1339 (Fed. Cir. 2015) (en banc). Dropped the strong presumption against applying 112(f) to claims that do not use the word “means”. A nonce term such as “module” followed by a function can still be a means-plus-function element.
Amgen Inc. v. Sanofi, 598 U.S. 594 (2023). A claim to an entire genus defined by its function must enable the full scope of the genus. Telling skilled artisans to make and test candidates by trial and error is not enough when the claims are that broad.

Practical notes

Section 112(a) caps what you can claim later. Amendments during prosecution must find support in the application as filed, and section 132(a) bars adding new matter. Describe alternatives, ranges with intermediate values, and the reasons each feature matters, so that you have support for narrower claims when the examiner cites art.

Functional language is the most common source of 112 trouble. If a claim says what an element does rather than what it is, either recite structure or make sure the specification describes the structure (for software, the algorithm, in prose or a flowchart) that a court would read into a 112(f) element.

Indefiniteness rejections are usually fixed by amendment: correct a missing antecedent basis, replace relative terms such as “about” or “substantially” with a standard from the specification, or define the term expressly. Our claim drafting guide covers the conventions.

Related rules and guidance

37 CFR: § 1.71, § 1.72, § 1.73, § 1.75, § 1.77
MPEP: 608, 2161, 2163, 2164, 2165, 2171, 2173, 2181