In exchange for the multi-year monopoly that a patent confers, the inventor has to hold up his end of the bargain with the U.S. government: He must teach how his invention works. That way, the public can make use of the invention once the patent expires.

U.S. law requires that the applicant for a patent provide a written description in “such full, concise, and exact terms as to enable any person skilled in the art… to make and use [the invention].” The patent statute additionally obliges the applicant to “set forth the best mode contemplated by the inventor of carrying out his invention.”(35 U.S.C. § 112).

These provisions impose the so-called “enablement” and “best mode” requirements on would-be patent owners.

The second of these requirements is the subject of the startling ruling this month inAnvik v. Nikon. Nikon persuaded a federal judge in Manhattan that the patentee hid the ball in obtaining a series of patents covering a high-resolution photolithography machine.

The machine covered by the patents is used in semiconductor processing to project numerous copies of a very detailed pattern onto a photomask so that the copies are tightly packed next to one another. This is used to create many identical, tiny circuits. The technology is used to produce flat panel displays, among other things.

Courts have, on occasion, invalidated patents that fail to disclose the best mode for practicing a claimed invention. Even defendants who seem clearly to infringe a claimed invention have persuaded courts that the patentee held back from the public some aspect of the invention that the inventor subjectively considered–at the time the application was filed–the best mode for practicing the invention.

The policy behind the harsh penalty of invalidation is to encourage full disclosure from inventors, or companies, that may perceive commercial advantage in keeping parts of an invention secret.

Absent a best mode requirement, an inventor might disclose a less practical embodiment of his invention, perhaps reserving an optimal one as a trade secret. This would do little to “promote the Progress of Science and useful Arts,” which is the constitutional objective of intellectual property protection.

This rationale has been controversial because it is rarely crystal-clear whether a particular approach or mode is crucial to effective operation of the invention, or is but one of various ways in which the invention might be practiced. In the latter instance, invalidation for its omission constitutes no more than a “gotcha” that allows a defendant to infringe with impunity.

Anvik had asserted three patents against Nikon. In the description and drawings of one of the patents, the illumination-system portion of the photolithography machine is treated as an undefined “box,” labeled with a letter but otherwise not discussed. An earlier patent application did describe the illumination system, although there is no reference to it in the later-filed application.

Nikon argued that the inventor, Dr. Kanti Jain, “intentionally gamed the system,” reckoning that if the first application failed to issue as a patent, he would have the consolation of keeping the illumination system secret. (The applications in question were filed long before 2000, when patent applications began to be published in the U.S.).

With no detailed discussion, Judge Alvin Hellerstein held all three patents invalid for failure to disclose the inventor’s best mode. The implications of the ruling are far-reaching, since Anvik has asserted its patents against several major display manufactures, and hefty sums are at stake. The judge’s ruling is likely to be appealed.

While an inventor remains legally bound to teach the best mode of practicing a claimed invention, the invalidity defense based on failure to do so is no longer available for cases filed after September 16, 2011, when the America Invents Act was signed into law. Section 282 of the Patent Act is now amended, explicitly excluding the contentious best mode defense as “a basis on which any claim of a patent may be canceled or held invalid or otherwise unenforceable.”

As with the new law’s most widely discussed departure from longstanding practice—the awarding of exclusive rights to the “first inventor to file” rather than the “first to invent”–the abrogation of the best mode defense brings the U.S. more in line with patent practice worldwide.

Accused infringers who seek to persuade a court that the patentee left out something important (and therefore should be prevented from enforcing his rights) will likely shift their attention to the patent law’s enablement requirement. This would alter a defendant’s attack strategy, as the enablement requirement obligates the inventor only to disclose some manner in which the invention can be practiced—not necessarily every manner or even the best manner.