© 2003, Dawsey Co., LPA
June 2003

Inventors get used to using the preamble in their claims to simply describe the intended use or ultimate object of the invention. As such, the language of the preamble is not usually construed as limiting the body of the claims that follow. However, danger lurks in preambles that move beyond a statement of purpose or use.

A recent decision by the United States Court of Appeals for the Federal Circuit, Eaton Corporation v. Rockwell, 2003 U.S. App. LEXIS 5904, showed that a preamble can be construed as limiting a claim.

Eaton and Rockwell (formerly known as Meritor) both manufactured transmissions for heavy duty trucks. At issue was U.S. Pat. No. 4,850,236 and the meaning of a long and detailed independent claim 14, of which about two-thirds of its wording was preamble. Meritor contended that Rockwell had infringed its patent.

The district court held a Markman hearing to construe the claims, and in an oral ruling construed only the limitations following the preamble. As a result of following the court’s construction of the claim, the jury found that Rockwell had infringed Meritor’s patent.

On appeal, Meritor argued that the lengthy preamble went far beyond a mere intended purpose, and had introduced structure that provided an antecedent basis for claimed material and was essential to understanding the reference terms used in the remainder of the claim. The Court of Appeals for the Federal Circuit agreed, finding that Rockwell “chose to use both the preamble and the body of the claim” to define the invention. Construing the entire claim, the court reversed and found that there had, in fact, been no infringement.

While this case turned on an exceedingly lengthy preamble, it contains a nugget of wisdom for all inventors. Make sure that the preambles of your claims are short and sweet, serving only to identify the invention, and not to define aspects of the invention. Otherwise, you may have introduced limitations that you never intended.