TAKEAWAY: MasterMine v. Microsoft provides further guidance regarding the difference between apparatus claims having permissible functional language versus impermissible method steps, as first addressed in IPXL Holdings v. Amazon.

On October 30, 2017, the Federal Circuit in MasterMine Software, Inc. v. Microsoft Corp. addressed the issue of indefiniteness under 35 U.S.C. § 112 ¶ 2 when claims improperly mix claim types. MasterMine sued Microsoft asserting infringement of U.S. Patent Nos. 7,945,850 and 8,429,518. The district court held that certain claims were invalid as indefinite for improperly claiming different subject-matter classes. On appeal, the Federal Circuit affirmed the district court’s claim construction, but reversed the district court’s determination of indefiniteness.

The Federal Circuit’s analysis of claim indefiniteness under 35 U.S.C. § 112 ¶ 2 began with a review of the court’s application of § 112 ¶ 2 in IPXL Holdings, L.L.C. v., Inc. – that a single claim covering both an apparatus and a method of use of that apparatus is indefinite. The court reasoned that claiming mixed subject matter creates confusion when determining infringement. The court then reviewed the case law following IPXL, noting that while claims cannot be directed to both a method and an apparatus, claims are not necessarily indefinite for using functional language. The court went on to explain that claiming a functional capability of an apparatus is permissible functional claiming, whereas claiming activities of a user of an apparatus in an apparatus claim is impermissible and indefinite.

The court then held that the claims at issue were not indefinite because they “merely use permissible functional language to describe the capabilities of the claimed system.” Thus, the Federal Circuit’s ruling here builds upon its holding in IPXL, offering further guidance to practitioners on how to avoid impermissible mixing of method apparatus recitations when drafting claims.