Best mode

Section 112(a) requires the specification to set forth the best mode contemplated by the inventor or joint inventor of carrying out the invention¹. The MPEP describes it as a safeguard against obtaining patent protection without making a full disclosure, and says it does not let inventors disclose only their second-best embodiment while keeping the best for themselves³.

Compliance is a two-prong inquiry. First, whether at the time of filing the inventor possessed a best mode, which is a subjective inquiry into the inventor's state of mind. Second, if so, whether the written description disclosed it so that a person skilled in the art could practice it, which is an objective inquiry³. The MPEP treats the best mode requirement as separate and distinct from enablement³.

Section 15 of the AIA did not eliminate the requirement for a disclosure of the best mode. Effective September 16, 2011, it amended 35 U.S.C. 282 so that failure to disclose the best mode is not a basis on which any claim of a patent may be canceled or held invalid or otherwise unenforceable³. The statute now lists the best mode exception inside the defense of failure to comply with section 112, so other section 112 requirements remain available as defenses².

• The claims define the invention. The specification need not set out details not relating to the essence of the invention, and unclaimed matter unrelated to the operation of the claimed invention does not trigger the requirement³.
• No specific example is required. The absence of a working example is not necessarily evidence that the best mode was not disclosed, and a preferred range of conditions can represent the best mode³.
• No label is required. The statute does not require inventors to point out which embodiment they consider best; it is enough that the disclosure includes the best mode contemplated³.
• No update is required. The MPEP says there is no requirement to update the best mode in the context of a foreign priority application under 35 U.S.C. 119, or in applications claiming the benefit of an earlier filing date under 35 U.S.C. 119(e) or 120³.
• Concealment is not needed for a rejection. Failure to disclose the best mode need not rise to the level of active concealment or inequitable conduct to support a rejection³.
• A missing best mode cannot be added later. An amendment adding a specific mode not described in the application as filed should be treated as new matter³. See New matter.

This page does not analyze other jurisdictions. For Europe, the text of Rule 42(1)(e) EPC says the description shall describe in detail at least one way of carrying out the invention claimed, using examples where appropriate and referring to the drawings, if any⁶. The rule does not use the term best mode, and this page does not state how European practice treats it.