The following article appears in the journal JOM, 47 (11) (1995), p. 69. JOM is a publication of The Minerals, Metals & Materials Society

Reading and Understanding Patent Claims

Those who are familiar with patents and patent law know that the invention is defined by the claims. Claims are often compared to the recitation of property lines in a deed for land because both show the property that the owner has the right to exclude others from trespassing on or infringing.

There are several situations where nonpatent professionals may need to read patent claims. One situation is when a patent application is being drafted and then subsequently prosecuted before the U.S. Patent and Trademark Office. As an inventor, you may be asked to review the claims that your patent agent or attorney has drafted. Once the patent application is filed and a patent examiner at the Patent and Trademark Office examines the claims, you may be called upon by your patent agent or attorney to assist him or her in either arguing that the claims are distinguishable from the cited prior art or in amending the claims to avoid relevant prior art. Another situation involving claim interpretation is when there is a potential issue of patent infringement. In this case, a product you make may be accused of infringing a patent owned by your competitor or vice versa.

The claims of a patent come at the end of the document, right after the written description (specification) of the invention. The claims are set forth as separately numbered paragraphs in a single-sentence format. The first claim of an issued patent is always numbered "1," with each claim thereafter following in an ascending numerical sequence. Most patents contain about 10-20 claims, although there are some patents with only one claim and others with hundreds of claims.

There are two types of claims—independent claims and dependent claims. As the names imply, independent claims stand alone and do not need to be read with other claims in order to interpret them. Dependent claims, on the other hand, have to be read in conjunction with the claim on which it depends. Hence, if you see a patent claim that states "The machine of Claim 1," the claim is a dependent claim that includes all of the limitations of the claim or claims from which it depends. The remainder of this article will focus on independent claims.

Each independent claim consists of three parts: the preamble, a transitional word or phrase, and the body.

The function of the preamble is to set forth the general technical environment of the invention. For example, a claim to an improved washing machine might have the preamble "A washing machine . . . ." The preamble is usually not considered to be a legally limiting constraint on the invention. The limiting constraints are found later in the body of the claim.

After the preamble, the next part of the claim is a transitional word or phrase. The transitional word or phrase comes between the preamble and the body. There are basically three transitions used: "comprising" or "which comprises," "consisting of," and "consisting essentially of."

The term comprising is what is known as an open term. In effect, comprising is a shorthand way of saying "including the following elements but not excluding others." For example, a claim to a combination comprising A + B covers a combination having A + B + C. In general, a patent attorney drafts claims containing a minimum number of elements that will function in a combination and uses the open term comprising in order to cover the invention as broadly as possible under the patent.

On the other hand, the term consisting of is a closed term. Returning to the example, a combination consisting of A + B does not cover the combination A + B + C. Closed language is usually found in chemical or metallurgical composition inventions where it is desired to exclude more than traces of other ingredients.

The final term, consisting essentially of, is part open and part closed. It is mainly used in chemical and metallurgical composition inventions and is a shorthand way of saying "excluding additional unspecified ingredients which would affect the basic and novel characteristics of the product defined in the balance of the claim." Thus, a claim to a combination consisting essentially of A + B language would cover a combination of A + B + C if C is not vitally important to the combination.

The body of the claim follows the transitional phrase and lists the main elements of the combination. It is here that the invention is particularly claimed. The body of the claim of a machine invention, for example, lists the parts of the machine in some sort of logical order so as to recite the mechanical interrelationship of the parts of the machine. In another example, the claims to a chemical invention may show a chemical formula or a representation of a chemical molecule. Finally, the claims to a method invention will list the method steps generally in the order in which they are to be carried out.

Because the claim is a single sentence, special punctuation conventions have been developed and are being increasingly used by patent attorneys. Modern claims follow a set format whereby the preamble is separated from the transitional term by a comma while the transitional term is separated from the body by a colon. Each of the elements of the invention in the body of the claim are in separate paragraphs, which are set apart from other paragraphs by a semi-colon.