Functional Language Renders Patent Claim Invalid


In a recent case, the court invalidated a patent claim due to the use of functional language. The plaintiff, AGIS, Inc., held a patent for a cellular communication system that allowed users to monitor the location and status of others through a visual display. However, one of the limitations of the patent claim, referred to as the “symbol generator,” was deemed indefinite and thus invalidating the claim.

The Accused Infringer’s Counterclaim

The defendant, Life360, had created a mobile app designed to enhance family connectivity. The app enabled users to view and communicate with their family members on a map, as well as receive alerts when they arrive at certain locations. To avoid patent infringement liability, Life360 argued that the claims in question were indefinite and therefore invalid.

The Issue of Indefiniteness

The argument centered around the language used in the patent claim, specifically the term “symbol generator.” This phrase was considered functional language, as it did not clearly define the structure associated with it. According to patent law, functional language is allowed in claims, but only if the patent discloses the structure associated with that function. In this case, the patent failed to describe any specific structure.

Expert Testimony

During the litigation, an expert witness for AGIS confirmed that the term “symbol generator” referred to a class of structures rather than a specific one. Although it represented a class, it still lacked clarity on the associated structure. As a result, the court concluded that the term constituted pure functional language, falling under the means plus function limitation.

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Means Plus Function Limitation

Under patent law, means plus function claims are restricted to the structure disclosed in the patent and associated with the stated function. If the patent fails to disclose any structure, competitors and defendants cannot determine whether they are infringing on the claim. Consequently, the claim is considered indefinite and violates patent regulations.

Claiming an Invention in Terms of Function

While it is possible to claim an invention in terms of its function, the scope is narrower than commonly believed. The claim must still include the particular structure described in the patent application related to that function. In this case, the court found the claims indefinite because the “symbol generator” language constituted pure functional language, without any specific structure disclosed.

The Importance of Clarity in Claiming an Invention

This case serves as a reminder of the importance of clarity when formulating patent claims. Care must be taken to clearly express the structure of any functional aspects of the invention included in the claims. It is crucial to continually review and analyze claim language to identify potential functional language and ensure compliance with patent requirements.


This case demonstrates the consequences of incorporating functional language without disclosing the associated structure in a patent application. It underscores the need for clarity when claiming an invention and emphasizes the importance of careful wording throughout the patent prosecution process. For assistance or further inquiries, contact Garrity Traina, an Orange County Patent Attorney, at Garrity Traina.