It is very important to provide adequate disclosure when using “means-plus-function” claims in a U.S. patent, particularly in the field of software. “Means-plus-function” claims include elements that are defined in a functional (as opposed to structural) manner, such as “means for tying a shoe”, and can be useful as long as they are carefully prepared. In particular, “means” claims require the disclosure of specific structural examples in the body of the patent that are used to interpret the functional elements.1

One further issue is that this requirement is often confused with the requirement that the patent include enabling disclosure.2 Enabling disclosure generally relates to whether an individual of ordinary skill in the art (i.e., a suitable engineer or programmer) could make or use the invention. On the other hand, providing adequate disclosure of corresponding structures is important, even where such structures may be routine, since this is necessary to ensure the claim is not indefinite.

The Genesis of Means-Plus-Function Claims

Means plus function claims have an interesting history. At the turn of the 20th century, functional claiming using “means” language was widely accepted. For example, the Wright brothers’ patent for a FLYING MACHINE claimed “means for simultaneously moving the lateral portions [of a wing] into different angular relations” and “means whereby said rudder is caused to present to the wind that side thereof...”3

In 1946, however, the U.S. Supreme Court grounded functional claiming in a case called Halliburton Oil v. Walker4, where the invention related to locating the surface of oil in a well using echolocation. In Haliburton, the Court found the patent to be indefinite since there was no disclosure of how the patent actually performed the claimed function. Means language that related to a desired function could not be used at the point of novelty in a claim.5

Congress responded in 1952 with legislative changes that specifically allowed patentees to use “means” language to claim a function. These claims, however, would not cover the entire function itself, but rather only the specific structures that accomplished this function and which were discussed in the patent. This restriction was intended to deny overbroad claim language, and leave open the possibility of competitive innovation (i.e., different structures that can accomplish the same function).

The recent case of Eon Corp v. AT&T6 reminds us that this requirement continues today in software patents that use means-plus function claims. In Eon, the Federal Circuit upheld a finding of invalidity related to a software patent that allowed a television to perform actions such as impulse buying, audience voting, and sorting shows by theme. The Court reviewed the requirements with respect to structure and enablement of software “means-plus-function” patents, including discussing two important earlier decisions: Katz7 and Aristocrat.8

A “general purpose computer” is not enough…

In the Aristocrat decision, the Federal Circuit had previously explained that the mere disclosure of a “general purpose computer” was insufficient to satisfy the disclosure requirements of means claims. The appellant in Aristocrat manufactured and sold gaming machines, and held a patent9 that disclosed a gambling game for a slot machine where players define their own winning combinations. Claim 1 recited “game control means” but the patent disclosed only a “general purpose computer” for performing this function, and in particular did not disclose the algorithm used to control play. The court held that:

“…Because general purpose computers can be programmed to perform very different tasks in very different ways, simply disclosing a computer as the structure designated to perform a particular function does not limit the scope of the claim to "the corresponding structure, material, or acts" that perform the function, as required [by the statute]...”

On the other hand, the Court explained that when an algorithm is disclosed that performs the claimed functions, even though that algorithm may be running on a general purpose computer, that computer becomes, in effect, a special purpose computer10 that will satisfy the statutory requirements for means claims.

…unless the claimed functions are “basic operations”

Following Artistocrat, the Court recognized an important exception in Katz. In this case, the appellant owned several patents that dealt with telephone processing and interactive call conferencing systems. The Court explained that a general purpose computer could provide sufficient structure to support a means-plus-function claim provided that the function is coextensive with the ordinary capabilities of the general purpose computer. In Katz, this was taken to include basic operations such as “processing”, “receiving”, and “storing”. Hence, the claims were not indefinite even though a specific algorithm was not disclosed, since a general purpose computer does not need special programming to perform these particular operations.

Eon Corp v. AT&T

In Eon, the appellant tried to argue that a general purpose computer could provide structure sufficient to satisfy the requirements for “means” claims so long as an ordinary person skilled in the art would know how to implement the invention. The Federal Circuit disagreed, explaining that the appellant had confused the requirement for enabling disclosure with the requirements related to means-plus-function claims. Whether or not a skilled programmer or engineer could understand how to build the invention was not relevant, since their knowledge could not be imported into the specification to provide structure for the means claims. Moreover, Eon’s attempt to rely on the Katz exception because the claimed functions were “simple to implement” was fruitless, as the Court explained that “…“special programming” does not denote a level of complexity.” Hence, Eon was unable to convince the Federal Circuit to “fill in the gaps” in the disclosure and overturn the finding of invalidity.

The Eon decision serves as a useful reminder about the need to be careful when using “means plus function” claims in U.S. patent applications, even in a software case where the specific functions that are claimed seem simple. With Aristocrats and Katz in mind, it is important to recall the distinction between enabling disclosure and scope-limiting disclosure. Moreover, while the narrow Katz exception does exists for functionality that is co-extensive with the “general-purpose computer”, in most cases a more detailed disclosure of an algorithm will be required for enforceable claims to exist in the United States.

Interestingly, the situation is slightly different here in Canada, as we do not have a comparable statutory requirement for “means” claims. Indeed, “means” claims are commonly used here, and our examination guidelines explain that they can be supported either by a description of the types of means contemplated, or by knowledge that would be obvious to a person skilled in the art.11Hence, Eon would likely have been much more successful in Canada with its “simple to implement” arguments.