Sometimes, non-US applicants will argue, “even assuming the Examiner’s proposed combination of prior art appears obvious, the proposed combination actually would not have been obvious. The reason is that the combination of the prior art cannot achieve the special effect of ____.”
This argument is basically a reverse-economic argument. That is, (a) the combination of art produces a special effect, and (b) the combination of references was allegedly obvious. However, if (a) and (b) are both true, why did no one combine the references? Surely, someone would have taken an obvious step to achieve the special effect!
In limited circumstances, this argument is useful in the US. For example, this argument is the primary way to address rejections based on rearrangement of parts under In re Japikse, 181 F.2d 1019, 86 USPQ 70 (CCPA 1950). MPEP 2144.04 VI C. Also, this argument is the basic idea behind “result-effective variable” responses to “routine experimentation” rejections. 2144.05 II.
However, this argument generally is not persuasive in the US. From the American point of view, the reverse-economic argument does not address whether the claims are prima facie obvious. That is, if the prior art suggests the claimed invention, then it does not matter there is an associated advantage. “The fact that [applicant] has recognized another advantage which would flow naturally from following the suggestion of the prior art cannot be the basis for patentability when the differences would otherwise be obvious.” MPEP 2145 II (citing Ex parte Obiaya, 227 USPQ 58, 60 (BPAI 1985)); id. (citing Lantech Inc. v. Kaufman Co. of Ohio Inc., 878 F.2d 1446, 12 USPQ2d 1076, 1077 (Fed. Cir. 1989), cert. denied, 493 U.S. 1058 (1990) (unpublished) (“The recitation of an additional advantage associated with doing what the prior art suggests does not lend patentability to an otherwise unpatentable invention.”)).
That is, from the American point of view, “rearrangement of parts” and “routine experimentation” are special cases, where the Examiner must close gaps in the prior art to arrive at the claimed invention. However, if there are no gaps in the prior art, a reverse-economic argument cannot establish patentability.