Obviousness is the ultimate condition of patentability. The obviousness requirement – that inventions must, to qualify for a patent, be not simply new but sufficiently different that they would not have been obvious to the ordinarily skilled scientist – is in dispute in almost every case, and it is responsible for invalidating more patents than any other patent rule. It is also perhaps the most vexing doctrine to apply, in significant part because the ultimate question of obviousness has an I know it when I see it quality that is hard to break down into objective elements. That hasn’t stopped the Federal Circuit from trying to find those objective elements. In the last quarter-century, the court has created a variety of rules designed to cabin the obviousness inquiry: an invention can’t be obvious unless there is a teaching, suggestion, or motivation to combine prior art elements or modify existing technology; an invention can’t be obvious merely because it is obvious to try; and so forth.

In KSR v. Teleflex, the Supreme Court rejected the use of rigid rules to decide obviousness cases. In its place, the Court offered not a new test, but a constellation of factors designed to discern whether the person having ordinary skill in the art (the PHOSITA) would likely think to make the patented invention. In short, the Court sought to take a realist approach to obviousness – to make the obviousness determination less of a legal construct and to put more weight on the factual determination of what scientists would actually think and do about a particular invention.

As a general principle, this realist focus is a laudable one. The too-rigid application of rules designed to prevent hindsight bias had led to a number or results that defied common sense, including the outcome of KSR itself in the Federal Circuit. But the realist approach has some (dare we say it) nonobvious implications for evidence and procedure, both in the Patent and Trademark Office (PTO) and in the courts. The greater focus on the characteristics of individual cases suggests a need for evidence and factual determinations, but the legal and structural framework under which obviousness is tested makes it difficult to make and review those determinations. The realist approach is also incomplete, because both the knowledge of the PHOSITA and the way the court approaches so-called secondary considerations of nonobviousness depend critically on the counterfactual assumption that the PHOSITA, while ordinarily skilled, is perfectly informed about the prior art. If we are to take a realist approach to obviousness, we should make it a consistent approach, so the ultimate obviousness determination actually reflects what scientists in the field would actually think. So far, despite KSR, it does not. The result of taking the realist approach seriously may be – to the surprise of many – a law of obviousness that is in some respects more favorable to patentability than the standard it displaced.