In order to diminish the extensive confusion surrounding claim preambles, one must not consider what a preamble should do; rather, it is helpful to consider what a preamble should not do. Traditionally, a preamble is defined as an introduction to a statute or deed stating the document’s basis, purpose, aim, justification, and objective. However, in patents, a claim preamble does not serve this purpose. While a preamble undeniably functions as an introduction to the rest of the claim, that claim is limited in scope and therefore, so too, is the preamble. The basis, purpose, aim, justification, and objective of the invention are properly contained elsewhere in the specification, not in the claim. Indeed it is the role of the specification, not the claim preamble, to shed light on the claim terms; to describe how to make and use the invention and to disclose the best mode contemplated for its use. None of this is within the purview of the claim, or its preamble, whose purpose is solely to highlight those novel and patentable aspects of an invention. Strengthened by this knowledge, the conscientious claim drafter will realize that while a carelessly worded preamble can be a liability, a well constructed preamble can be a powerful asset.
Kyle D. Petaja, Claim Preambles And The Unassailable Patent Claim, 5 J. Marshall Rev. Intell. Prop. L. 121 (2005)