It is a tradition in patent drafting to refer to one or more examples as “preferred” or as a “preferred embodiment.” While these “preferred embodiments” reside in the specification, they can influence the interpretation of the claims. The role of preferred embodiments in claim construction was the issue in two cases, Laitram Corp. v. Cambridge Wire Cloth Co. and Vitronics Corp. v. Conceptronic, Inc. These cases represent two different lineages of the case law that refer to preferred embodiments, where application of these cases broadens (or prevents narrowing of) claim scope. Laitram warns against confining the claim to a specific example disclosed in the specification, where the example is a preferred embodiment. Vitronics warns that the claims should not be interpreted in a way that excludes the preferred embodiment. Where an example is labeled as “preferred,” this labeling almost always works to the advantage of the patentee during litigation. But, this labeling can also backfire against the patentee, resulting in claim invalidation. Two arguments can turn the preferred embodiment against the patentee. The first causes the claim to fall under the scope of the prior art, resulting in invalidation under 35 U.S.C. § 102. The second invokes the best mode requirement, thereby demanding a high degree of enablement under 35 U.S.C. § 112. Where a high degree of enablement is required, it can raise the question of validity for lack of enablement.
Tom Brody, Preferred Embodiments in Patents, 9 J. Marshall Rev. Intell. Prop. L. 398 (2009)