The Problem With Using Functional Language in Patent Claims

MARK TERRY, ESQ.

In Ex parte Zurcher, the Board addressed an apparatus claim that used functional language. The examiner cited prior-art structure capable of performing the stated function, even though the structure differed from the embodiment shown in the applicant’s specification.

The Board emphasized that patentability is determined by the claims, not by unclaimed structural details in the specification. It also explained that an inherent feature does not need to have been recognized by a skilled artisan before the relevant date.

Applicants may define an element structurally or functionally, but functional language carries risk. Once the Patent Office has reason to believe prior-art structure can perform the claimed function, the applicant may need to establish that it cannot.

Lessons learned: When apparatus structure is important to patentability, structural claim language is often safer. A claim stated only in terms of intended function may read on physically different prior art that is nevertheless capable of producing the same result.