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Posted Wednesday, October 17, 2012 by Mike Cicero

The use of alternative language in patent claims is generally rejected by the United States Patent and Trademark Office (“PTO”) because alternative language fails to particularly point out and distinctly claim the invention. However, alternative language may be used if it presents “no uncertainty or ambiguity with respect to the question of scope or clarity of the claims.” MPEP 2173.05(h). The applicant in Ex parte Markush, used a claim form that defined a genus by enumeration of the species. 1925 C.D. 126 (Comm’r Pat. 1925). During examination the claim was objected to for being in the alternative form and applicant, Eugene A. Markush, petitioned to the Commissioner. Ultimately, the claim form was approved of and has since been referred to as a “Markush” claim.

A Markush claim properly recites alternatives in the form ”wherein the unyielding material is selected from the group consisting of A, B, and C.” Such a form is particularly helpful when there is no simple generic expression to define the desired genus, which is commonly referred to as a “Markush Group”. For example, the materials aluminum, zinc, copper, lead, and calcium are all members of the non-ferrous metals genus. Consider an invention in which an unyielding material will come into contact with a beverage during normal use. A claim reciting “wherein the unyielding material is a non-ferrous metal” may be undesirable because lead has toxic properties, and is thus unsafe for contact with food, and calcium reacts violently with water. Under these circumstances, the applicant may choose to use the claim language ”wherein the unyielding material is selected from the group consisting of aluminum, zinc, and copper,” or in short form ”wherein the unyielding material is aluminum, zinc, or copper.”

A requirement for a proper Markush claim is that the members of the explicitly enumerated genus must bear a physical or chemical relationship to one another. The degree of the relationship required is not absolute. Ordinarily, the members must belong to a recognized physical, chemical, or art-recognized class. In the example used above, because the members of the Markush group all belong to the chemical and art-recognized class of non-ferrous metals they bear a sufficient relationship to one another to form a proper Markush group.

Markush-style claims can be a good way to explicitly claim a large number of variations of the claimed invention. However, there is the risk that one species of a Markush claim will be anticipated by the prior art which, in turn, may be interpreted as anticipating the entire claim. During prosecution an applicant would be able to cancel the member of the Markush group that causes the claim to be anticipated which may put the claim in allowable form, but if this happens after prosecution is closed, during litigation for example, this may prove fatal to a claim for proving patent infringement. Due to this concern, it is often wise to include claims reciting the preferred versions of the invention in a more narrow form even if literally covered by a broader Markush claim. For example, notwithstanding the inclusion of the claim language ”wherein the unyielding material is aluminum, zinc, or copper” in one broad claim it may be desirable to further include a more narrow claim using the language ”wherein the unyielding material is aluminum.” Even though this practice is redundant, i.e. the latter claim language is literally covered by the former claim language, if the aluminum version is preferred and the former claim is anticipated by prior art disclosing the zinc or copper version, the applicant’s preferred version will still be protected (assuming the preferred version remains non-obvious). If economically feasible, the most preferred version should be included as a completely separate and independent claim.

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