In Shoes by Firebug LLC v. Stride Rite Children’s Group, [2019-1622, 2019-1623] (June 25, 2020), the Federal Circuit affirmed the PTAB’s determination that the challenged claims of U.S. Patent Nos. 8,992,038 and 9,301,574, directed to illumination systems for footwear, were obvious.

The most interesting part of the case is one that made no difference to the outcome: when a preamble limits a claim and when it doesn’t. A preamble limits a claim if it recites essential structure or steps, or if it is necessary to give life, meaning, and vitality to the claim. Conversely, a preamble is not limiting where a patentee defines a structurally complete invention in the claim body and uses the preamble only to state a purpose or intended use for the invention.

The body of claim 1 of the ’038 patent recites a structurally complete invention, and therefore the preamble’s recitation of an “internally illuminated textile footwear” is merely an intended purpose that does not limit the claims. A preamble is not limiting ‘where a patentee defines a structurally complete invention in the claim body and uses the preamble only to state a purpose or intended use for the invention. Unlike claim 1 of the ’038 patent, claim 1 of the ’574 patent does not reintroduce “footwear” in the body of the claim but instead relies on the instance of “footwear” introduced in the preamble for “antecedent basis.”

But it makes no difference: Although the Board did not construe the preamble as limiting, the prior “suggests using a woven, porous material in a light diffusing, internally illuminated part of footwear,” making the claims of both patents obvious.

Small differences in working can make a big difference in interpretation; decide whether you want the preamble to be a limitation and word the application and specification accodingly.