When a Patent examiner rejects an Applicant's claim as being obvious, the Examiner will sometimes rely on teachings from a reference that is from a different technology than the claimed invention. The doctrine of "Analogous Art" may apply to such a situation, where only prior art that is analogous to the claimed invention may be properly used.  While examiners often assert that a prior art reference is still relevant even when it fails to solve the particular problem solved by the inventors, if the prior art reference is not from the same field of endeavor binding precedent expressly rejects such assertions.  

There are two ways for prior art to be analogous: 1) if the reference is from the same field of endeavor as the claimed subject matter; or 2) if the reference is still reasonably pertinent to the particular problem with which the inventor is involved. When a reference only qualifies under the second prong, there is an often times ignored additional requirement, the subject of the present post. Namely, as set forth by the Federal Circuit in in re Klein 647 F.3d 1343 (Fed. Cir. 2011), a prior art reference in a separate field of endeavor will not be analogous art unless it is pertinent to the entire problem being solved by the challenged patent.  Even the Patent Trial and Appeal Board (PTAB) understands this distinction and has even relied on it to find a claimed invention to a refrigerator shelf patentable after institution of an IPR.  (Schott Gemtron Corporation v. SSW Holding Company, Inc., IPR 2014-00367, Final Written Decision, 2015).  In this IPR, the prior art showed a microscope slide with the missing claimed element, but used the feature to contain a sample, not to enable improved used of shelf space as described (but not claimed) in the patent being challenged.

The takeaway is that when an Examiner cites a reference in an obviousness rejection that is from a different field of endeavor, then that reference may only be used if it is relevant to the entire problem solved by the claimed invention.  An applicant can typically craft the definition of the problem to include something more than what is solved by the reference (possibly through argument and/or claim amendments), and thus should typically be able to put forth a strong argument to overcome the rejection.