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For some people , because the claims define the invention that is protected by the patent they are the most important feature of the patent. They provide guidance to competitors in steering clear of the patent. They indicate the scope and limitations of the patent so that a court can determine if the patent is infringed. The claims follow a set format.
The first part of the claims is the “preamble”, which states in general terms what the invention relates to. Examples of preambles are "a bicycle”, “nucleic acid"," a pharmaceutical composition”, “a method for treating arthritis “, “a device for accelerating wound healing”.
The wording of the preamble does not affect the scope of the patent protection.
Following the preamble is a “connector” which is usually either “comprising”; “consisting of”; or “consisting essentially of”. The choice of connector is very important and has a tremendous impact on the breadth of the patent.
The word "comprising” in a claim means that the patent will be infringed by an article, device or a process that contains all of the features described in the claim, even if the potential infringer includes additional features. For example, if a claim mentions a table comprising four legs and a top, the patent will be infringed by a table having five legs, or having four legs, a top and a shelf below the tabletop.
Conversely, the term “consisting of” in a claim means that the patent will be infringed by anything that contains all of the features of the claimed invention, but will not be infringed if it contains additional features.
Because the term “consisting of” significantly narrows a patent claim, it is generally avoided by patent attorneys unless it is felt to be necessary in order to avoid very close prior art.
The term “consisting essentially of “ is seen occasionally in patent claims in the biological and chemical fields. It means that a patent claim will be infringed if a potential infringer contains all the features of the claimed invention plus additional features that do not substantially change the nature of the invention. In the case of a pharmaceutical composition, the presence of an additive that enhances the effect of the patented composition, such as by increasing its shelf life or its potency, will infringe the patent. On the other hand, the presence of an additional ingredient that changes the nature of the composition, for example, that makes it unsuitable for use as an acne medication but makes it suitable for increasing cardiac output, would not infringe the patent.

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