The following article appears in the journal JOM, 53 (2) (2001), p. 64. JOM is a publication of The Minerals, Metals & Materials Society

Claim Interpretation Under the Doctrine of Claim Differentiation

Because patent claims define the scope of the patent owner’s exclusionary rights, a correct analysis of the scope of the claims is critical to any evaluation involving patent claim infringement and validity.

While, in some instances, the scope of a given claim is clear, in others ambiguities may exist. This often results in the need to apply certain rules of claim interpretation. For example, when the meaning of a term used in a claim is not clear, an enhanced understanding may come from the description of the invention contained in the specification. Also to be considered is how the term would be interpreted by one skilled in the particular technical art.

One important rule of interpretation is the “doctrine of claim differentiation.” This doctrine, in effect, assumes that two claims in the same patent will not have the identical scope, but instead, that there is likely an intended difference in scope between the two.

A patent specification must describe an invention in such detail that one skilled in the art to which it pertains is enabled to practice the invention without having to engage in undue experimentation. Part of the policy underlying the U.S. patent system is that the inventor is rewarded for his or her disclosure of the invention to the public with a right, for a limited time, to exclude others from making, offering for sale, selling, using, and importing the claimed invention. After expiration of the patent, the public has free use of the invention. The failure to provide an enabling disclosure would result in the inventor getting the benefit of the exclusionary right during the term of the patent, but the public not getting the full benefit of free use of the invention thereafter.

The disclosure of the specification need not recite every way known to the inventor of practicing the invention. It must, however, disclose the “best mode” of practicing the invention as of the filing date of the application. Patent claims, if adequately supported by the specification, can, and generally do, claim more broadly than the specifics disclosed in the application, unless precluded by relevant prior art.

Most patents contain one or more independent claims and a series of dependent claims which depend directly or indirectly on an independent claim. A dependent claim must be read as if the language of the claim or claims from which it depends were also part of the dependent claim. It is, in effect, an incorporation by reference. The specification might disclose a method of making a fruit juice beverage and disclose generically the concept of employing a citrus fruit, with specific reference to oranges and grapefruits.

An independent claim might read: (1) A method of making a fruit drink beverage comprising providing a citrus fruit, squeezing said citrus fruit to express the juice therefrom, admixing said juice with about 10–30 weight percent water, and adding a sweetener to said admixture of juice and water.

Dependent claims 2 and 3 might read as follows: (2) The method of making a fruit juice drink of claim 1 including employing lemons as said citrus fruit. (3) The method of making a fruit juice drink of claim 1 including employing as said fruit a fruit selected from the group consisting of oranges and grapefruits.

In the foregoing situation, if one were to use any citrus fruit and follow the steps of the claim 1 method, one would infringe claim 1. Claim 2 would be read as containing all of the recitals of claim 1, but be limited to a citrus fruit which was a lemon. As a result, one using an orange or grapefruit would not infringe claim 2. One using an orange or grapefruit would infringe claim 3. Patent claims typically offer a gradation of scope with the independent claim being the broadest claim, meaning it is the easiest to fall within or infringe, but by definition will be closest to the prior art and, therefore, if a challenge to validity is available, would be the most vulnerable claim. By contrast, the dependent claim, such as claim 2, is narrower and more difficult to infringe, but as a result of the narrowing, may be farther from the prior art and, therefore, have potentially greater validity strength.

If one, in this oversimplified example, were to employ the process using a lime and a question of infringement of claim 1 were raised, the alleged infringer might argue that claim 1 must be interpreted as being limited to oranges and grapefruits. Limiting claim 1 to use with oranges and grapefruits would be a rewriting of the claim to incorporate disclosure from the specification in an impermissible manner. Applying the doctrine of claim differentiation, one looking at claims 2 and 3 would state that the express reference to a lemon in claim 2 makes it clear that claim 1 was intended to have a scope broader than merely oranges and grapefruits. More significantly, claim 3 would be rendered meaningless with its recital of the fruit being an orange or a grapefruit if claim 1 were interpreted as being limited to oranges and grapefruits. In effect, claim 3 would be redundant. The rule of construction regarding claim differentiation, therefore, would result in the conclusion that rather than assuming that both the inventor and the Patent and Trademark Office intended to grant a patent with two identical claims (claims 1 and 3), the more logical assumption is that the term “citrus fruit” was to have a broader meaning than oranges and grapefruit and would permit full application of the genus. This would result in claim 1 being interpreted as covering a method of making a fruit drink beverage employing the steps recited with any citrus fruit.

It should be kept in mind that more than one rule of claim construction may be involved in interpreting the scope of a given claim. For example, if the specification had stated “as employed herein the term ‘citrus fruit’ means all fruit falling within the genus except for limes,” claim 1 would be interpreted as being broader than the use of oranges or grapefruits, but not embracing the use of limes.

The foregoing analysis focuses on the issue of whether there is literal infringement of a patent claim (i.e., whether a given practice satisfies every recital of the claim.) Infringement can also exist under certain circumstances by a broadened interpretation of the claim under the doctrine of equivalents which was the subject of an article in this series appearing in the May 1990 issue of JOM, “The Doctrine of Equivalents in Patent Infringement.” This concept might be applicable if one were to apply the doctrine of claim differentiation and conclude that, for some reason, the claims were limited to oranges and grapefruits. The doctrine of equivalents states, in general, that if one avoids literal infringement, but employs essentially the same method in essentially the same way to achieve essentially the same result, one may be held to be an infringer. In this example, there could be an issue under the doctrine of equivalents of whether one using a tangerine would infringe claim 1.

Arnold B. Silverman is chair of the Intellectual Property Department and a member of Eckert Seamans Cherin & Mellott, LLC in Pittsburgh, Pennsylvania.

For more information, contact A.B. Silverman at Eckert Seamans Cherin & Mellott LLC, 600 Grant Street, 44th Floor, Pittsburgh, Pennsylvania 15219; (412) 566-2077; fax (412) 566-6099; e-mail abs@escm.com.