What is the best mode requirement in patent law?
The best mode requirement is a patent disclosure obligation that compels inventors to reveal, in the specification, the best way they know of to practice their claimed invention at the time they file. It exists as a safeguard against inventors obtaining patent protection without making a full disclosure, preventing a scenario where an inventor discloses only a second-best embodiment while concealing superior alternatives.
Statutory basis
The requirement appears in the second clause of 35 U.S.C. § 112(a), which states that the specification "shall set forth the best mode contemplated by the inventor or joint inventor of carrying out the invention." This sits alongside the enablement and written description requirements in the same subsection, but best mode is a separate and distinct obligation from both.
The two-part test
Courts apply a two-part inquiry to evaluate compliance:
First (subjective) prong: At the time of filing, did the inventor know of one mode of practicing the claimed invention that the inventor considered better than all others? This prong is entirely about the inventor's actual, subjective state of mind. If the inventor had no preference among available modes, there is nothing concealed and the prong is satisfied.
Second (objective) prong: If a best mode existed, does the written description adequately disclose that mode so that a person skilled in the art could practice it?
Both prongs must be met. The Federal Circuit adopted this framework in Chemcast Corp. v. Arco Indus. Corp., 913 F.2d 923 (Fed. Cir. 1990), and it remains the governing analytical structure.
Scope: defined by the claims
The boundary of the best mode inquiry follows the claims. The obligation applies to the subject matter of the claimed invention: material unrelated to the claimed subject matter need not be included, and unclaimed matter unconnected to the claimed operation does not trigger best mode concerns. The requirement is not a general obligation to disclose every piece of technical knowledge the inventor possesses; only modes of carrying out what is claimed are in scope.
Evaluated at filing: no update obligation
The best mode requirement looks to the filing date. There is no obligation to update the specification to reflect improvements or refinements the inventor discovers after filing. What governs is the inventor's state of knowledge on the day the specification is submitted.
This also means best mode is assessed at one fixed moment. A specification that adequately discloses the inventor's preferred approach as of filing is compliant, even if the inventor later develops a superior technique that goes unmentioned.
What counts as concealment
Not every omission constitutes a best mode violation. The standard requires evidence of concealment, whether intentional or accidental: the disclosure quality must be so poor that it effectively conceals the best mode from the skilled reader.
Information that is well-known among practitioners in the field need not be spelled out. Unintentional omissions of techniques readily known in the field do not constitute concealment.
Two Federal Circuit cases mark the boundary clearly:
Violation found: In Spectra-Physics, Inc. v. Coherent, Inc., 827 F.2d 1524 (Fed. Cir. 1987), inventors of a laser failed to disclose their preferred TiCuSil brazing method. The method ran contrary to the technical literature and was not in the prior art; it was affirmatively withheld, and a violation was found.
Violation found: In Dana Corp. v. IPC Ltd. P'ship, 860 F.2d 415 (Fed. Cir. 1988), an inventor knew that a specific surface treatment was necessary for the product to perform satisfactorily but did not say so in the specification. Even though the surface treatment technique itself was known in the art, withholding the fact that it was necessary for performance constituted a violation.
No violation: Where the omitted information is routine to practitioners in the field and the inventor did not deliberately withhold it, courts have declined to find a best mode problem.
The Dana Corp. pattern is worth internalizing: a violation can exist not because the technique itself is secret, but because the inventor concealed its necessity. Disclosing a technique while omitting that it is required for successful practice can be just as problematic as omitting the technique entirely.
No explicit labeling required
An inventor need not designate any embodiment as "the best mode" or include a statement identifying the preferred approach. It is sufficient that the best mode is disclosed somewhere in the specification without that label. Courts ask whether the disclosure contains the best mode, not whether the inventor has pointed a finger at it.
Separately, the best mode need not be expressed as a single specific example. A preferred range, a preferred class of compounds, or a preferred process window can satisfy the requirement if it reflects the inventor's actual preference.
Omissions cannot be cured by amendment
If the best mode was not disclosed in the original specification, there is no procedural path to fix the omission through prosecution. An amendment that introduces a previously undisclosed practicing mode constitutes improper new matter and is not permissible. The best mode must be present in the originally filed application; it cannot be grafted on later.
Best mode vs. enablement
These are separate and distinct requirements that can fail independently. Enablement asks whether the specification places the claimed subject matter in the possession of the public, that is, whether a skilled practitioner can make and use the full scope of the claimed invention from the disclosure. Best mode asks the narrower question of whether the inventor's privately preferred approach has been included.
A disclosure can enable a broad genus while the inventor withholds a preferred subgenus. A disclosure can fully reveal the inventor's best mode while failing to enable the full scope of a broad claim. Satisfying one requirement does not satisfy the other, and office actions on each must be addressed independently.
AIA impact on invalidity proceedings
Before the America Invents Act (AIA), best mode failure was an available invalidity defense in patent litigation: an accused infringer could argue that the patent was unenforceable because the inventor had withheld the best mode. The AIA removed that route. Under 35 U.S.C. § 282(b)(3)(A), failure to disclose the best mode "shall not be a basis on which any claim of a patent may be canceled or held invalid or otherwise unenforceable."
This change applies only to civil proceedings. The requirement to disclose best mode under § 112(a) remains in place as a USPTO examination obligation, and examiners are entitled to reject applications that show evidence of concealment. In practice, however, best mode rejections are extremely rare in ex parte prosecution because examiners have no access to the inventor's private state of mind at the time of filing.
Practical notes for practitioners
| Situation | Best mode consideration |
|---|---|
| Inventor has a preferred commercial source for a key material | Consider disclosing the preferred source or a functionally equivalent description if that preference is not obvious from the state of the art |
| Internal testing has identified a preferred range within a broader claimed range | Include the preferred range; omitting it in favor of a generic range may raise a best mode concern if the preference was known at filing |
| Best mode is present in a parent or priority application but not the continuation | Confirm what was disclosed at the filing date of each application in the chain; the filing date of each application controls its own best mode inquiry |
| Litigation opponent raises best mode invalidity post-AIA | Point to § 282(b)(3)(A): best mode failure is no longer an available invalidity or unenforceability defense in civil proceedings |
- Interview the inventor before filing about preferred embodiments. Ask whether there is a preferred material, supplier, process step, range, or component for each element of the claimed invention. Answers that differ from what is in the draft specification create a checklist for disclosure before filing.
- Best mode is tied to subjective preference, not objective superiority. The question is what the inventor considered best, not what independent testing would prove best. If the inventor had no settled preference, document that fact; it supports that the first prong is not met.
- The AIA reduced litigation risk but did not eliminate prosecution risk. The duty to disclose is unchanged, and evidence of concealment that surfaces during inter partes proceedings can still complicate prosecution history. A clean disclosure is the surest protection.
- Commercial sensitivity does not relieve the duty. The policy behind best mode is designed to ensure full disclosure as the quid pro quo for patent rights. An inventor who wants to keep a preferred method confidential faces a genuine tension when filing: the preferred method may need to be disclosed in the specification, which becomes public.
- Post-filing fixes are not available. Build the habit of confirming best mode coverage before the application is filed, because any gap discovered afterward cannot be cured by amendment without adding new matter.