Patent practice thrives on fine distinctions between a new invention and the prior art. From the fertile field of fine distinctions grow rules of thumb, generalizations, presumptions, sayings, and canards intended to be helpful. Discussed here is "routine optimization," an approach to obviousness in cases where the gap between the prior art and patent claims appears to be one that the hypothetical person of ordinary skill in the art would necessarily bridge in the ordinary course of development.

The origin of "routine optimization" as an indicium of obviousness. Patents may not grant to "obvious" inventions. 35 U.S.C. §103(a) (patent may not be obtained "if the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious … to a person having ordinary skill in the art"). To facilitate the examination of patent applications, examiners may reject claims that are prima facie obvious over the prior art. If the examiner makes a prima facie showing, the burden shifts to the applicant to come forward with evidence to rebut the examiner's case. Because the burden shifts to the applicant only if the examiner's prima facie showing was adequate, precedent developed around the standard of adequacy, including cases holding that types of differences that commonly separated a proposed claim from the prior art were sufficient to support an examiner's prima facie showing.

One such rule was a difference that could be bridged by "routine optimization." In re Aller, 220 F.2d 454, 456 (CCPA 1955) ("where the general conditions of a claim are disclosed in the prior art, it is not inventive to discover the optimum or workable ranges by routine experimentation"). For example, In re Huang, 100 F.3d 135 (Fed. Cir. 1996), concerned a patent application on dual-layer, shock-absorbing grips for tennis racquets. The player's hand gripped an outer layer of polyurethane, which was bonded to an inner textile layer. Such dual-layer grips were known in the prior art, but the applicant found that increasing the thickness of the polyurethane layer relative to the textile layer "greatly improved" the grip's shock absorbing qualities. The PTO rejected the claims, finding the prior art taught that the thickness of polyurethane is a variable "the optimization of which is obvious." Id. at 137.