The patent statute makes it clear that subject matter that would have been obvious to one of ordinary skill in the art as of the effective filing date of a patent application is not patentable. The considerations relevant to obviousness have been set for some time: (1) the scope and content of the prior art; (2) the level of ordinary skill in the art; (3) the differences between the claimed subject matter and the prior art; and (4) secondary considerations of non-obviousness. There has, however, been much litigation on how courts are to apply these considerations to determine whether an invention would have been obvious and therefore not patentable. Early on when faced with the issue, the courts envisioned a hypothetical person of ordinary skill in an art at the relevant time in a room with all of the relevant prior art. Then the court would evaluate what that hypothetical person would find obvious with this assumed knowledge of the prior art. Of course, this has proven more difficult than it sounds. Disputes have arisen as to what the relevant scope of the art should be and what motivation if any would be required for this hypothetical person to combine the art to come up with the claimed invention. One consistent aspect of this analysis has been that hindsight could not be used; the evaluation must be made with the information known to one skilled in the art at the relevant time.
The Supreme Court, in KSR Intl. v. Teleflex, Inc., attempted to clarify the proper analysis for an obviousness determination. In KSR, the Court rejected a rigid formulation for the determination of obviousness in holding that the Federal Circuit’s “teaching, suggestion and motivation” test was not the only appropriate analysis. The Court in KSR made it clear that the scope of the prior art includes the creativity of one skilled in the art and the results of routine experimentation where there are known options with a finite number of identified predictable solutions. At the same time, the Court continued to warn against the improper use of hindsight.
With respect to anticipation, the concept of inherency has been around for some time. A claimed invention can be inherently anticipated even though all the elements of the claimed invention are not explicitly described in the prior art, if when the teaching of the prior art is followed the claimed invention will necessarily and inevitably result. There is no requirement that anyone at the relevant time understood the inherent quality of the prior art to support an argument of inherent anticipation. The logic of this position is clear – if the claimed element is inherent in the prior art then the prior art cannot be practiced without infringing the claimed invention. Since it is inappropriate for a patent claim to cover what already exists in the prior art, the claim is anticipated.
The worlds of inherent anticipation and obviousness appear to be colliding. Courts are addressing obviousness arguments that rely upon inherent aspects of the prior art. It is not yet entirely clear what all the parameters are for such arguments, but it is evident that inherency is now undoubtedly a part of the obviousness analysis.
The Federal Circuit has historically been skeptical with respect to using an inherent teaching in an obvious analysis. The court recognized that inherency and obviousness are distinct concepts. Indeed, the court has held that to establish obviousness based upon an inherent property in the prior art, that inherent property would have to be obvious to those skilled in the art at the relevant time. It had been clear that a retrospective view of inherency is not a substitute for some teaching or suggestion supporting obviousness.
More recently, however, the Federal Circuit has indicated that, at least in some circumstances, inherent properties of the prior art are an appropriate part of the obviousness analysis even if the inherent properties were not previously appreciated. In EMI Group v. Cypress Semiconductor, when reversing the grant of a JMOL that the claims were not invalid as anticipated or obvious, the court conducted an inherent anticipation analysis but it never actually set forth an obviousness analysis or provided any basis for its obviousness conclusion.  The case is directed to fuses used in integrated circuits. The patent at issue claimed a fuse that was composed of metal having a cap of refractory metal. The claims required that when the fuse is exposed to an energy source (generally a laser) there would be “explosive removal” of the fuse from the circuit. The court found that a fuse of the structure called out in the claim existed in the prior art, but the art did not teach the “explosive removal” set forth in the claim. The Federal Circuit also found that the record below supported a finding that the claimed “explosive removal” was an inherent feature of the structure when an energy source is applied to the prior art fuse. The court concluded “[t]he district court, therefore, improperly granted JMOL that the claims of the ‘785 and ‘801 patents are not invalid for anticipation and obviousness.” The court clearly set out the basis for inherent anticipation, but the basis for the court’s obviousness conclusion is not evident. The court could have simply been saying that the claims are inherently anticipated and therefore JMOL on the validity issue was improperly granted, i.e. obviousness was just along for the ride. But the language the court chose certainly opens the door to the argument that a previously unknown inherent quality of the prior art can be used to support an obviousness argument.
In In re Huai-Hung Kao, the Federal Circuit considered the validity of a claim directed to a controlled release oxymorphone composition that required a “food effect” wherein the Cmax blood concentration of the active compound was at least about 50% higher when the dosage form was administered with food as compared to fasted conditions.  The Patent Office had found that the recited sustained release pharmaceutical composition of the claim was obvious over the prior art, despite the fact that there was no teaching of the claimed food effect in the prior art. On appeal the applicant argued that “an obviousness rejection can only be based on what is known by those skilled in the art at the time of the invention, and there is no evidence in the record that anyone recognized the claimed food effect at that time.” The Federal Circuit found that there was substantial evidence that the food effect was an inherent property of oxymorphone regardless of how it was formulated. The court concluded by stating that “[t]his is not a case where the Board relied on an unknown property of the prior art for a teaching. Rather [the prior art’s] express teachings render the claimed controlled release oxymorphone formulation obvious, and the claimed “food effect” adds nothing of patentable consequence.”
Thus, at least in this case, because the court found that a claim limitation was inherent in the prior art, it was irrelevant to the obviousness analysis. This analysis seems to be the case regardless of the fact that the inherent property was not appreciated in the prior art.
In Allergan v. Sandoz Inc., the court found not obvious a method claim for using a composition that had previously been found to be obvious.  In rebutting the dissent’s view that the method claim should have been obvious, the court explained the use of inherency in anticipation and obviousness evaluations, stating:
The dissent would find claim 4 obvious on the grounds that it merely claims the result of treatment with an obvious composition. In support of its position, the dissent cites a series of cases in which the patentee claimed either a previously unknown result or an undisclosed inherent property of an otherwise anticipated claim. In the context of anticipation, “[n]ewly discovered results of known processes directed to the same purpose are not patentable because such results are inherent.” Bristol-Myers Squibb Co. v. Ben Venue Labs., Inc., 246 F.3d 1368, 1376 (Fed. Cir. 2001). We agree with the dissent that the inherency doctrine may apply to an otherwise obvious claim as well. There is, however, a problem with applying the doctrine in this case.
The evidence of record does not establish that the [claim limitation] is an inherent property or a necessary result of the administration of the [obvious composition]. Of course it may be true that the mere administration of the [obvious combination] twice a day in any fixed combination inherently produces the claimed result. Alternatively, it may also be true that only certain fixed-combination formulations produce this result. On the present record, we cannot draw a conclusion in favor of either proposition.
It should be noted that in Allergan, the defendant never argued that the claim limitation at issue was inherent in the method. The outcome may have been the other way had the court had a record that would support inherency of the missing claim limitation.
In the most recent statement on the issue from the Federal Circuit in Par Pharmaceutical v. TWI Pharmaceuticals, Inc., the court set forth a test for the application of inherent obviousness:
A party must, therefore, meet a high standard in order to rely on inherency to establish the existence of a claim limitation in the prior art in an obviousness analysis – the limitation at issue necessarily must be present, or the natural result of the combination of elements explicitly disclosed by the prior art.
In Par Pharmaceutical, the court reversed a finding of obviousness that was based on the inherent presence of a claim limitation. It was undisputed that the inherent feature was not appreciated by those skilled in the art. The court did not find that relying on an unappreciated inherency to support an obviousness position was improper; to the contrary the court seemed to endorse the approach. The court did, however, hold that on the record before them the defendant (and the District Court) had not established that the claimed limitation was inherent in the art, and as such the District Court had applied the incorrect standard for inherency. In so holding, the court stressed that the standard for proving inherency is a high one.
From the recent case law it is clear that the obviousness analysis cannot be assumed to be limited to that information that was known in the art. Inherent characteristics, even an unappreciated inherent characteristic, of the prior art should be considered when evaluating an obviousness position. The issue is even more interesting when it is appreciated that the asserted inherency relates to subject matter that never existed in the prior art. Rather, the subject matter would exist only as the combination of multiple prior art references created during litigation. It is not clear how an inherent teaching will affect all obviousness cases. As always, the facts of each case may dictate the outcome. However, it is hard to reconcile the use of unappreciated inherent qualities of the prior art to support obviousness with the constant admonition of the courts against the use of hindsight. In In re Huai-Hung Kao, the court avoided this issue by reading the inherent limitation out of the claim stating it “adds nothing of patentable consequence.” But how is that conclusion even possible without the use of hindsight when no one in the prior art recognized the inherent characteristic? Moreover, does it make any sense to find something obvious over the prior art when there is admittedly no evidence that the prior art (including those of ordinary skill in the art) ever appreciated it?
Further, if unappreciated inherent qualities of the prior art can be used to prove obviousness, should they not also be available to refute obviousness? In Bristol Myers v. Teva, the Federal Circuit held that an unknown characteristic of the prior art was not available to refute obviousness because the normally skilled artisan was not aware of the characteristic at the appropriate time.  In Bristol Myers, the prior art compound, upon which the obviousness position was based, was discovered to be toxic to mammals after the filing of Bristol Myers’ patent application. The court held that the fact that the prior art compound was toxic and that the claimed compound was not, could not be used to support non-obviousness. One of the reasons the court reached this conclusion was that prior to the filing of the patent application, the toxicity of the prior art compound was not known and the prior art compound was being used in research. While the court never referred to the toxicity of the prior art as an inherent characteristic, there is no indication anywhere that the compound was only sometimes toxic. The court’s refusal to allow the patentee to rely upon a later discovered characteristic of the prior art to establish a distinction between the prior art and the claim invention is hard to reconcile with the court’s reliance on unappreciated inherent characteristics of prior art to establish a lack of non-obvious distinction between the prior art and the claimed invention. It would seem that the evidence, if useable at all, should be usable to establish either obviousness or non-obviousness as the case may be.
Perhaps the answers to these questions become a little clearer when the nature of the inherent characteristics in these cases is analyzed. In each of the cases where the court relied on the inherent characteristic, it was functional in nature – “explosive removal” in EMI; “food effect” in Kao; “without a loss of efficacy” in Allergan. In each case the claim limitation is the result of using or treating a known or obvious composition of matter. This application of the law is analogous to logic used when finding inherent anticipation with respect to a claim directed to an unappreciated result. Specifically, when the court has found that a claim limitation is inherent in the prior art (whether appreciated or not), the court has sometimes found that the claimed characteristic (inherent in the art) does not sufficiently distinguish the prior art combination so as to make it non-obvious. The court has simply been unwilling to allow inventors to reserve for themselves something inherent in an obvious derivative of the prior art, even though the combination of the prior art does not explicitly teach the invention.
This aspect of the law is clearly still evolving. As the courts are confronted with ever-changing fact situations, the role of inherency in determining obviousness should become clearer. It is believed, however, that patent challengers will still have an uphill battle – inherency is often difficult to prove. No matter how the case law evolves, one thing has become clear: whether litigating or prosecuting patents, when addressing an obviousness issue, counsel is going to have to consider whether a claim limitation is inherent in the teaching of the prior art.
 35 U.S.C. § 103 (A patent may not be obtained “if the differences between the claimed inventions and the prior art are such that the claimed invention as a whole would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art to which the claimed invention pertains.”).
 Graham v. John Deere Co. of Kan. City, 383 U.S. 1, 17-18 (1966).
 See Union Carbide Corp. v. Am. Can Co., 724 F.2d 1567 (Fed. Cir. 1984).
 See KSR Int’I Co. v. Teleflex Inc., 550 U.S. 398 (2007).
 Id. at 421 (“A person of ordinary skill is also a person of ordinary creativity, not an automaton.”).
 See, e.g., Leggett & Platt, Inc. v. VUTEk, Inc., 537 F.3d 1349, 1354 (Fed. Cir. 2008) (“Under the principles of inherency, if the prior art necessarily functions in the accordance with or includes, the claims limitations, it anticipates.”); see also In re Montgomery, 677 F.3d 1375, 1379 (Fed. Cir. 2012).
 See In re Cruciferous Sprout Litig., 301 F.3d 1343, 1349 (Fed. Cir. 2002) (“Inherency is not necessarily coterminous with the knowledge of those of ordinary skill in the art. Artisans of ordinary skill may not recognize the inherent characteristics of functioning of the prior art.”) citing MEHL/Biophile Int’l Corp. v. Milgraum, 192 F.3d 1362, 1365 (Fed. Cir 1999).
 Kloster Speedsteel AB v. Crucible Inc., 793 F.2d 1565, 1576 (Fed. Cir 1986),
 Id.;see also Application Spoorman, 363 F.2d 444, 448 (C.C.P.A. 1966) (“That which may be inherent is not necessarily known. Obviousness cannot be predicated on what is unknown.”).
 In re Rijckart, 9 F.3d 1531, 1534 (Fed. Cir. 1993).
 EMI Grp. N. Am., Inc. v. Cypress Semiconductor Corp., 268 F.3d 1342 (Fed. Cir 2001).
 Id. at 1345.
 Id. at 1351.
 In re Huai-Hung Kao, 639 F.3d 1057 (Fed. Cir. 2011).
 Id. at 1070 (It should be noted that the Patent Office specifically argued that inherency is part of the obviousness inquiry and the Federal Circuit agreed).
 Id. (emphasis in original).
 See also Santarus, Inc. v. PAR Pharm., Inc., 694 F.3d 1344, 1354 (Fed. Cir. 2012) (The court held that blood serum levels where an inherent property of the formulation and that the claim to an obvious formulation cannot be rendered non-obvious by simply adding an inherent property (resulting serum blood concentrations) as a limitation to the claims.).
 Allergan, Inc. v. Sandoz Inc., 726 F.3d 1286, 1294 (Fed. Cir. 2013).
 Id. at n.1.
 PAR Pharm., Inc. v. TWI Pharm., Inc., 2014 WL 6782649, at *7 (Fed. Cir. Dec. 3, 2014).
 Id. at *6.
 Id. at *8.
 Id. at *6.
 Id. at *7.
 639 F.3d at 1070.
 Bristol-Myers Squibb Co. v. Teva Pharm. USA, Inc., 752 F.3d 967 (Fed. Cir 2014).
 Id. at 974.
 When the denying the petition for rehearing/en banc consideration, multiple explanations surfaced as to why the evidence was not considered. Judge Dyk and Judge Wallace asserted that post invention evidence should not be allowed in the obviousness analysis in the circumstances of this case. Read broadly this runs contrary to the established practice of using post invention evidence to establish secondary considerations. More likely these judges are referring to the using the evidence in the establishment of a prima facie obviousness case, i.e., defining the differences between the claimed invention and the prior art. Judge O’Malley argued that the evidence was considered but considered not persuasive. Judges Newman, Laurie, Reyna and Taranto all dissented arguing that the evidence should have been considered.
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