At the end of every patent is a numbered list of patent claims. Unlike the text that precedes them, the claims very specifically define what is patentable about the invention. If the patent is ever challenged, the court will look to the language in the claims. These claims are often written by a patent attorney, who may use very abstract language that seems impenetrable to those not skilled in claim drafting. The structure of each claim complies with rules set forth in the Manual of Patent Examination Procedures, commonly known as the MPEP.
A claim may be independent or dependent. An independent claim contains the essential elements of the invention. A dependent claim contains all the elements of the independent claim as well as other elements. You can distinguish between dependent and independent claims because a dependent claim will always state which independent claim it depends from.
All claim begin with a preamble. The preamble often states whether the invention is an apparatus, a method or an improvement. For example, the preamble of an independent claim to a camera lens might read "An apparatus for visualizing an image" or "A method for generating images" or "An improved method for generating images." The preamble of a dependent claim will state the claim it depends from. For example, it might read "An apparatus as in claim 1."
The preamble is followed by a simple transitional phrase. Common transitional phrases are "comprising the steps of," "consisting of the following elements," and "including the elements." One important aspect of the transitional phrase is whether the verb is limiting. The verbs "including" and "comprising" are understood to be open-ended. While the invention includes whatever elements follow these verbs, it could also include other, different elements. The word "consisting" means that the invention is limited to those elements that follow the transitional phrase.
A list of elements follows the transitional phrase. These elements might be parts of the invention or steps for using the invention. If the elements are parts of the device, the claim is often referred to as an "apparatus claim." If the elements describe how to use the device, the claim is often referred to as a "method claim." Each element is often separated by semicolons and appears on a new, indented line of text.
An independent claim for a lightbulb might read: "1. An apparatus for generating light, including the elements of a housing; a filament; and a means for coupling said housing to a power source." A dependent claim might read: "2. An apparatus as in claim 1, wherein said filament is made of metal."