One of the many changes included in the Leahy-Smith America Invents Act relates to the date that a U.S. patent application is effective as prior art. While eliminating the Hilmer doctrine and giving prior art effect to U.S. patent applications as of their foreign priority dates might seem to be a step towards international harmonization, it actually may widen the gulf between the U.S. and the rest of world.

The Hilmer Doctrine

The current version of 35 USC § 102(e) provides

A person shall be entitled to a patent unless—

(e) the invention was described in – (1) an application for patent, published under section 122(b), by another filed in the United States before the invention by the applicant for patent . . . except that an international application . . . shall have the effects for the purposes of this subsection of an application filed in the United States only if the international application designated the United States and was published . . . in the English language

This means that a published U.S. patent application (or published PCT application that designated the U.S. and was published in English) can be cited as prior art as of its U.S. (or PCT) filing date.

The Hilmer doctrine, based on the 1966 CCPA case of In re Hilmer, holds that such an application is not citable as of its foreign priority date. That is, under the Hilmer doctrine, a foreign priority claim can be used as a shield against intervening prior art, but not as a sword against intervening inventions.

Patent Reform Eliminates The Hilmer Doctrine

New 35 USC § 102(a)(2) (which takes effect March 16, 2013) eliminates the Hilmer doctrine and gives prior art effect to U.S. patent applications as of their foreign filing dates:

(a) NOVELTY; PRIOR ART.—A person shall be entitled to a patent unless—

(2) the claimed invention was described in a patent issued under section 151, or in an application for patent published or deemed published under section 122(b), in which the patent or application, as the case may be, names another inventor and was effectively filed before the effective filing date of the claimed invention.

This change means that U.S. applications with foreign priority claims will be citable up to 12 months earlier than they are now, assuming that the PCT or U.S. Paris Convention application was filed 12 months after the foreign priority application was filed.

Eliminating Hilmer Does Not Promote International Harmonization 

While eliminating the distinction between a U.S. priority date and a foreign priority date might seem to be a step towards international harmonization, it actually may have an opposite effect because the U.S. puts patent applications to a much more expansive prior art use.

The ability to cite patent applications based on their filing dates creates a cache of “secret” prior art, because most patent applications are not published until 18 months after their earliest filing date. Most countries restrict the use of such secret prior art to the limited purpose of establishing novelty. Unless the application fully teaches the invention at issue, it only can be cited as of its publication date, not as of its priority date. However, the U.S. is unique in permitting the use of such applications for any purpose, including to establish obviousness.

By extending the reach of U.S. patent applications back to their foreign filing dates without restricting their use to novelty, the new law will create even more prior art that can be cited against a U.S. application to establish obviousness but cannot be cited against a corresponding foreign application to defeat inventive step. Thus, the operation of this aspect of patent reform in the context of other aspects of U.S. patent law will undermines rather than promote international harmonization.