navigating the patent maze

Like preambles for books, a claim preamble introduces the subject matter that follows.  A claim preamble is meant to name or define the thing that is to be claimed — e.g., "A sewing machine", "A transgenic yeast cell".  Preambles may also relate the purpose of the invention — e.g., "A sewing machine for stitching leather", "A method for transforming a yeast cell". 

A question about preambles often arises in the context of whether or not someone is infringing a claim.  For example, in the case of a claim preamble written as "an unleaded gasoline suitable for combustion in an automotive engine", would use of the claimed unleaded gasoline in a boat engine be infringing?  In patent law terms, does the language of the claim preamble limit the scope of the claim? 

The basic rule is that generally the preamble does not limit the claims; however, a preamble is limiting "if it recites essential structure that is important to the invention or necessary to give meaning to the claim."  Thus, if the preamble merely states the intended use or purpose of the invention, it usually does not limit the scope of the claim.  Of course, "usually does not limit" begs that there are times when it does limit the scope. 

Applying the basic rule to the example of the unleaded gas, if you concluded that it doesn’t matter what kind of engine the claimed gas composition is used in - you are right!   The stated use - in automotive engines - is an intended use, but not the only use.  (Union Oil Co v ARCO)   

Overall though, an inquiry into whether a preamble limits claim scope may require a review of the patent and patent record to determine what invention the patent intended to define and protect.  Here are some times when courts have concluded that preambles are limiting:

• when the preamble recites essential structure of the invention;
• when the preamble terms are necessary to give meaning to the claim;
• when a term in the rest of the claim refers back to the term in the preamble;
• when the preamble recites additional structure or steps highlighted in the patent texzt as important (or "preferred").