concurring in part and dissenting in part:
I concur in the result in No. 83-2193 (Stapleton/Westmoreland affirmed), in the result in No. 84-1528 (Comett/Mullins affirmed in part and reversed in part), and in Part III B of Judge Hall’s opinion dealing with prejudgment interest.
I dissent from the result in No. 84-1520 (Ray/Jewel Ridge reversed) and I disagree with major elements of the opinions of Judge Hall, Judge Widener, and Judge Sprouse respecting the meaning and application of 20 C.F.R. § 727.203, the “interim presumption” regulation.
I
I note at the outset that my perception of our proper function in interpreting this “interim presumption” regulation may differ in a critical respect from that of my brethren who come to different interpretations than mine. As I read their opinions, they reflect (though in different degrees) a general perception that we are free to interpret this regulation in the same way that we would interpret any statute or procedural rule having the force of statute, drawing on logic and legal reasoning and aided by the ordinary canons of statutory construction (including the “plain meaning” canon) to divine the promulgators’ intent as reflected in the regulation’s text.
The problem with that approach here is two-fold. First, we are not interpreting a statute or procedural rule having statutory force, but an agency’s regulation promulgated by authority and direction of Congress. Second, we have before us the agency’s own interpretation of the regula*440tion’s intended meaning and operation in the context of the cases we are reviewing.1
In this situation, our interpretive role in judicial review is narrowly circumscribed. It is not direct, free “construction” of the legal meaning of the regulation’s text, but something quite different. We should address, in sequence, only two questions.
First: whether the agency’s interpretation is “plainly erroneous or inconsistent with the regulation”? United States v. Larionoff, 431 U.S. 864, 872, 97 S.Ct. 2150, 2155, 53 L.Ed.2d 48 (1977). If it is not so, that interpretation is the “ultimate criterion” for determining legal meaning, and has “controlling weight” for that purpose. Id. (citing and quoting Bowles v. Seminole Rock Co., 325 U.S. 410, 414, 65 S.Ct. 1215, 1217, 89 L.Ed. 1700 (1945)).
Second: If the agency’s interpretation passes that deferential test and thereby supplies the regulation’s legal meaning, whether the regulation as so construed is “consistent with the statute under which [it was] promulgated”? Larionoff 431 U.S. at 873, 97 S.Ct. at 2156. The regulation’s ultimate validity — whether it has the force of law — may turn on this. Id.
In effect, this requires that we take the agency’s interpretation as the starting point for our judicial review of the disputed issue of the regulation’s legal meaning. Agency interpretation controls and has the force of law unless it is in the first instance “plainly erroneous or inconsistent with the regulation” itself or, beyond that, would yield a meaning for the regulation that is inconsistent with the authorizing statute. Only if the agency’s interpretation were impérmissible as interpretation or produced an invalid regulation should we decline to apply the regulation as so interpreted (and possibly substitute our own “saving” interpretation). See generally K. Davis, Administrative Law, § 7.22 (2d ed. 1980).
Applying these principles of judicial review, I would hold the agency’s interpretation here not plainly erroneous or inconsistent with the regulation, and the regulation as so interpreted not inconsistent with the authorizing statutes. On that basis, I would interpret and apply the regulation in accordance with the agency’s interpretation rather than any conflicting one that we might come up with as a matter of original and independent construction, including that partially conflicting interpretation reached here by the en banc court.2
*441II
The first question is whether the agency’s interpretation is “plainly erroneous or inconsistent with the regulation.” In addressing that, our only tools are “the plain words of the regulation and any relevant interpretations of the [agency].” Bowles, 325 U.S. at 414, 65 S.Ct. at 1217.
The agency interpretation, as presented in the Director’s brief, can be summarized and paraphrased in its most salient aspects as follows.
1. Under the proof scheme of 20 C.F.R. § 727.203, which creates a rebuttable presumption of compensable black lung disability, both claimant and operator bear opposing burdens of persuasion, the former to invoke the presumption, the latter to rebut the presumption if it is invoked.3
2, Under § 727.203(a)(l)-(4), the claimant bears the initial burden of proving specified factual predicates: (a) that he is 1 a miner who engaged in coal mine employment for at least 10 years, and either that (b), as established by X-ray, biopsy, or autopsy, he has pneumoconiosis, § 727.-203(a)(1), or that (c) as established by ventilatory studies, he has a chronic respiratory or pulmonary disease as measured by specified clinical requirements and values, § 727.203(a)(2), or that (d), as demonstrated by blood gas studies, he has a specified clinical level of impairment of his system’s ability to transfer oxygen from lungs to blood, § 727.203(a)(3), or that (e), as established by “[o]ther medical evidence, including the documented opinion of a physician exercising reasoned medical judgment,” he has a totally disabling respiratory or pulmonary impairment, § 727.203(a)(4).
3. If the claimant invokes the presumption by proving (a) and any one (or more) of (b)-(d), he has established a prima facie case of compensable disability. The burden of persuasion thereupon shifts to the operator to rebut the presumption, failing which the claimant is entitled to benefits.
4. Under § 727.203(b)(l)~(4), the operator’s burden of proof in rebuttal may only be carried by proof of facts that negate elements of the disability claim vel non that were not established to invoke the presumption. Thus, the presumption may be rebutted (a) by proof that the claimant is in fact doing or is able to do his usual coal mine work or comparable and gainful employment, unless the presumption was invoked by proof under § 727.203(a)(4) that claimant had a totally disabling respiratory or pulmonary impairment, § 727.203(b)(1), (2); or it may be rebutted (b) by proof that the disability established did not in fact arise in whole or in part out of coal mine employment, whatever the basis for invocation of the presumption, § 727.203(b)(3); or it may be rebutted (c) by proof that the claimant does not have pneumoconiosis, unless the presumption was invoked by proof under § 727.203(a)(1) that claimant does have pneumoconiosis, § 727.203(b)(4).4 5
*4425. The burdens of persuasion borne by both claimant and operator respectively are burdens to prove the relevant facts by a preponderance of the evidence.
6. In applying this presumption-based proof scheme, claim adjudicators are required to consider “all relevant medical evidence,” both in assessing whether the presumption has been invoked and whether it has then been rebutted.
I do not see how this interpretation, either in its general sweep or in its specific parts, could be declared “plainly erroneous or inconsistent with the regulation,” looking, as we are required to do, only to the “plain words of the regulation” and the agency’s interpretation of its own handiwork.
It is notorious in legal scholarship that the nature and intended operation of evidentiary presumptions rank among the greatest conceptual puzzles in the law. Attempts to categorize presumptions in systematic ways have long occupied and divided our best procedural scholars. See generally McCormick on Evidence §§ 342-344 (3d ed. 1984). Only the most artful and knowledgeable legislative drafting (or judicial opinion) is likely to produce an evidentiary presumption whose intended operation — whether as rebuttable or irrebuttable, “bubble-bursting” or more drastic, etc. —is manifest from its plain text. Given the conceptual and practical difficulties involved, it is therefore no reproach to the drafters of the “interim presumption” of 20 C.F.R. § 727.203 to start with the proposition that this presumption’s intended operation is by no means manifest from its “plain words.” That very fact, however, makes it difficult to find any particular interpretation of its intended operation “plainly erroneous or inconsistent” in relation to its text. So it is with the Director’s interpretation.
Looking first to the overall sweep of that interpretation, it might possibly be thought “plainly erroneous” if it comported with no known pattern of presumptions. But that cannot be said. While its most distinctive feature — casting persuasion burdens both to invoke and then to rebut the presumption — is not the only or even the most common presumption pattern, it is certainly one not unknown in traditional usage. See generally id. at § 344, pp. 974-76.
Neither is there any internal inconsistency within the Director’s interpretation of the presumption’s basic operation that might be thought to make it “plainly erroneous.” Indeed, the Director’s interpretation makes sense as a matter of practical operation. As so interpreted, the regulation meshes the opposing burdens of proof in a coherent proof scheme that addresses and permits resolution, without conflicting findings, of all elements of the basic statutory claim of black lung disability: (a) that claimant is a miner (b) who has pneumoco*443niosis (c) due to mine employment (d) that totally disables him. 30 U.S.C. §§ 901(a), 902.
Turning next to the most critical specifics of the Director’s interpretation, the plain words of the presumption do not negate the Director’s interpretation that the proof burdens borne by both sides are persuasion burdens under a preponderance of evidence standard. The most directly operative word suggesting the nature of the burdens borne, both as to invocation and rebuttal, is “establish.”6 In common usage this imports proof of a fact, see Alabama By-Products Corp. v. Killingsworth, 733 F.2d 1511, 1514 (11th Cir.1984), rather than the mere production of evidence of a fact’s existence. Cf, e.g., Texas Department of Community Affairs v. Burdine, 450 U.S. 248, 253, 101 S.Ct. 1089, 1093, 67 L.Ed.2d 207 (1981) (in interpreting the judicially constructed presumption of disparate treatment in Title VII litigation, “articulating” a non-discriminatory reason connotes a mere burden of production). While a persuasion burden interpretation may not be compelled by the word “establish,” that interpretation is surely consistent with the term. Indeed, it would appear to be the interpretation most consistent with the regulation’s “plain words.” Certainly it would be a questionable interpretation that found different burdens connoted by the same word “establish” as used on opposite sides of the presumption.7
The Director’s related interpretation that “all relevant medical evidence shall be considered” both in assessing invocation and rebuttal of the presumption, finds flat support in the plain words of the regulation.8 While the clause so stating appears in the rebuttal subsection, § 727.203(b), of the regulation, it is found there in an introductory passage which refers to the total process of “adjudicating a claim under this subpart,” i.e., Subpart C, which deals at large with the “Criteria for Determining Eligibility for Benefits.” Certainly this aspect of the Director’s interpretation cannot be declared plainly erroneous or inconsistent in relation to the regulation’s text.
Ill
There remains only the question whether the regulation as interpreted by the Director consistently with its text is nevertheless inconsistent with the statutes under which it was promulgated. Again, I do not see how it could be so found; indeed, it is perfectly consistent with both the letter and spirit of the relevant statutes.
The relevant statutory authorization begins by giving to the Secretary of Labor the responsibility and commensurate power to define by regulation the meaning of compensable black lung “total disability.” *44430 U.S.C. §§ 902(f)(1), 921(b). This general power to define is obviously not unlimited; it is constrained in certain respects relevant to the Director’s interpretation of 20 C.F.R. § 727.203, but the Director’s interpretation lies well within all the statutory constraints. I take these in order.
1. By statute, any regulations promulgated must provide that a living miner is “considered totally disabled when pneumoconiosis prevents him or her from engaging in gainful employment requiring the skills and abilities comparable to those [of his or her former mine employment].” The regulation as interpreted by the Director is consistent with this statutory constraint, by expressing it as a basis for rebutting the presumption by disproving the presumed fact of total disability. 20 C.F.R. § 727.-203(b)(2); see also 20 C.F.R. § 410.412(a)(1).
2. By statute, the regulation may not “provide more restrictive criteria than those applicable under Section 423(d) of Title 42,” the criteria for establishing “disability” for disability insurance purposes under the Social Security Act. Under the Director’s interpretation, a black lung claimant’s proof burden to establish disability is significantly lighter than is that of a social security disability insurance claimant. The black lung claimant need only establish, by any of various clinical tests, that he suffers one of specific medical conditions in order to place the burden of disproving his total disability from mine-employment related pneumoconiosis upon his employer. 20 C.F.R. § 727.203(a)(l)-(4). By contrast, the social security disability claimant must establish a disabling impairment that at least prevents his return to former work to place on the government the burden of disproving his compensable disability. See Hall v. Hams, 658 F.2d 260, 264 (4th Cir.1981). The black lung criteria provided by § 727.203 are therefore significantly less restrictive than are those imposed on social security disability claimants.
3. By statute, the regulations may not impose criteria more restrictive than those applicable to Part “B” claims. 30 U.S.C. § 902(f)(2). The criteria are now identical, hence, there is no inconsistency with this statutory constraint.
4. Built into the statutory criteria for determining black lung disability is a 10-year “rebuttable presumption” that pneumoconiosis suffered by a miner with ten or more years of mine employment is employment related. 30 U.S.C. § 921(c)(1). The interim presumption of 20 C.F.R. § 727.203 is clearly consistent with, indeed directly implements, this special proof dispensation conferred on claimants by statute.
5. By statute, any regulations promulgated are made expressly subject to the provisions of 30 U.S.C. § 923(b). 30 U.S.C. § 902(f)(1). Among the provisions of § 923(b) is the provision that “no claim for benefits ... shall be denied solely on the basis of the results of a chest roentgenogram.” As interpreted by the Director, the interim presumption is not inconsistent with this limitation on the denial of claims. Nothing in the Director’s interpretation prevents a claim adjudicator, in assessing “all relevant evidence,” including X-rays, from honoring this provision. The statutory provision simply makes impermissible any adjudication either that the presumption has not been invoked or that it has been rebutted “solely on the basis of the results of a chest [X-ray]” (emphasis supplied).9 Conformably with the Director’s *445interpretation, a single negative X-ray may not therefore be drawn upon either as the sole basis for finding the invocation burden under (a)(1) not carried nor as the sole basis for finding the rebuttal burden under (b)(4) carried.
Accordingly, neither in its general nor any of its specific aspects does the Director’s interpretation give the regulation a meaning inconsistent with the authorizing statutes. That interpretation should therefore be accepted and applied by the court in conformity with the principles of construction expressed in Bowles and Larionoff
IV
Judge Hall’s interpretation conflicts with that of the Director in two critical respects.10 First, it would hold that the claimant’s burden of proof to invoke the interim presumption is only a burden to produce evidence meeting one of the “medical requirements” of § 727.203(a)(l)-(4), i.e., one positive X-ray, or one set of qualifying ventilatory or blood gas studies, or one physician’s opinion and that if such evidence meets “pertinent standards for quality and authenticity,” conflicting “like kind” evidence cannot be weighed against it. P. 436.11 Second, it would hold that “ ‘non-qualifying test results ... cannot be used as the principal or exclusive means of rebutting an interim presumption of pneumoconiosis’ under 20 C.F.R. § 727.203(b),” although such test results “may be part of the rebuttal inquiry ... and are particularly relevant when they are given a detailed interpretation by an examining physician in reaching a medical conclusion as to a claimant’s impairment.” Id. (emphasis in original).
The first of these holdings would require us to overrule our panel decision in Consolidation Coal Co. v. Sanati, 713 F.2d 480 (4th Cir.1983), while the second would require us to reaffirm the panel decision in Whicker v. United States Department of *446Labor Benefits Review Board, 733 F.2d 346, 349 (4th Cir.1984).
Laying aside all concerns of deference to the agency’s interpretation of its own regulation, and with all respect to Judge Hall’s conflicting view, I think that view is simply wrong as a matter of original interpretation of a text’s legal meaning. On that basis, independently of any special deference to the Director’s contrary interpretation, I would interpret the regulation as does the Director and in consequence would reaffirm the critical holding in Sana-ti 12 and overrule that in Whicker and its precursor, Hampton v. United States Department of Labor Benefits Review Board, 678 F.2d 506 (4th Cir.1982).
Though, as indicated, there are a number of detailed respects in which I think Judge Hall’s interpretation is logically flawed, the underlying flaws are in its violation of the statutory mandate that “[i]n determining the validity of claims ... all relevant evidence shall be considered,” 30 U.S.C. § 923(b), and in its failure to appreciate the interrelation of the invocation and rebuttal elements of the interim presumption of 20 C.F.R. § 727.203.
An unmistakable consequence of this interpretation would be to preclude the consideration in many cases of highly relevant medical evidence respecting the validity of black lung disability claims. For example, under that interpretation, if a claimant merely “produces” one positive X-ray, i.e., one that a reader has “read positive,” and that meets “pertinent standards of quality and authenticity,” this effectively precludes the fact-finder’s consideration, at any stage, of conflicting X-ray evidence, no matter what its relative quality and quantity. From such possibly meager, but uncontrovertible, evidence of the existence of a mere trace of pneumoconiosis, profound consequences ensue. The central element of the claim — that pneumoconiosis exists— is conclusively established. Additionally, the other elements of the claim — that the condition is due to mine employment and is totally disabling — are established unless rebutted by evidence that carries the burden of persuasion to disprove the presumed facts. Furthermore, the employer may then be prevented from rebutting the presumed facts of causation and totally disabling effect by bringing to bear what may be the very best and most trustworthy clinical evidence of the actual nature and extent of any respiratory or pulmonary impairment suffered by the claimant — ventilatory and blood gas studies. For that evidence may not be relied upon as the “principal or exclusive” means of rebuttal.13
With all respect, such a consequence seems to me to reveal the unacceptability of such an interpretation of this presumption’s intended operation. Indeed, it might well draw the constitutionality of such an *447interpretation in question by making the presumption effectively irrebuttable under some circumstances. See Usery v. Turner Elkhorn Mining Co., 428 U.S. 1, 36-37, 96 S.Ct. 2882, 2902, 49L.Ed.2d 752 (1976) (constitutionality of statutory or regulatory presumptions may turn on admissibility of all medical evidence relevant to their rebuttal). For as I read this proposed interpretation, if a claimant invokes the presumption by putting in evidence one (or more) X-rays read positive for pneumoconiosis, and the employer then offers in evidence the testimony of any number of the most highly qualified medical experts that, based principally upon the results of properly administered ventilatory and blood gas studies, they are of the opinion that the claimant is not significantly disabled by any respiratory or pulmonary condition, that evidence simply may not be considered in rebuttal of the presumed fact of total disability by reason of pneumoconiosis.
With deference, it seems to me that the court got off the track in Whicker (actually in Hampton v. United States Department of Labor Benefits Review Board, 678 F.2d 506 (4th Cir.1982), which Whicker followed with modest refinement) in failing to recognize that such rebuttal evidence is not aimed at disproving the “established” fact of the existence of pneumoconiosis, but at the presumed fact of resulting total disability. See Whicker, 733 F.2d at 348. When this point is appreciated, consideration of such rebuttal evidence does not, as the Whicker panel saw it, “foree[] the claimant to come forward with proof of pneumoconiosis by two or more accepted testing techniques before he could derive any practical benefit from the interim presumption.” Id. It merely gives the employer a fair opportunity — which may be constitutionally required — to prove, if proof is available, that any pneumoconiosis had is not totally disabling within the statutory meaning. Other circuits have so held. See Drummond Coal Co. v. Freeman, 733 F.2d 1523, 1527 (11th Cir.1984); Peabody Coal Co. v. Lowis, 708 F.2d 266, 275 (7th Cir.1983). Of course, bare “non-qualifying” test results offered in evidence without supporting medical interpretation related directly to the degree of disability revealed might well not suffice to carry the rebuttal burden. See Peabody, 708 F.2d at 274. But it surely goes too far flatly to preclude all consideration of a qualified medical opinion of non-disability based, even “principally,” upon such clinical test results. Id. at 275.
V
Following the above analysis, I would interpret 20 C.F.R. § 727.203 as follows, conformably with the Director’s interpretation.
1. A living claimant may invoke the presumption that he is totally disabled by pneumoconiosis due to mine employment by proving by a preponderance of the evidence (a) that he is a miner, (b) that he worked for at least 10 years in coal mines, and (c) that (1) he has pneumoconiosis, as established by X-ray or biopsy results, or
(2) he has a respiratory or pulmonary impairment, as established by ventilatory studies yielding specified clinical values, or
(3) he has a blood-oxygen impairment, as established by blood gas studies yielding specified clinical results, or (4) he has a totally disabling respiratory or pulmonary impairment as established by other medical evidence including the documented opinion of a physician. 20 C.F.R. § 727.203(a)(1)-(4) .
2. Whether the “medical requirements” of (l)-(4) have been established is determined by weighing, under a preponderance of evidence standard, the type evidence required and produced as to each. For this purpose, no more than one such item (i.e., one positive X-ray under (a)(1)) may suffice, depending upon its quality and the quality and quantity of any opposing X-ray evidence. However, a single negative X-ray may not be relied upon to prevent proof of the existence of pneumoconiosis by a preponderance of the evidence under (a)(1). 30 U.S.C. § 923(b).
3. Invocation of the presumption under (a)(1) conclusively establishes that the *448claimant has pneumoconiosis; it raises a further rebuttable presumption that the pneumoconiosis arose out of mine employment, see 30 U.S.C. § 921(c)(1), and that it is totally disabling, see 30 U.S.C. § 902(f)(1).
4. Invocation of the presumption under (a)(2) or (a)(3) conclusively establishes only that the claimant has certain levels of respiratory or pulmonary impairment; it raises the further rebuttable presumption that the impairment results from pneumoconiosis, that the pneumoconiosis arose from mine employment, and that it is totally disabling.
5. Invocation of the presumption under (a)(4) conclusively establishes that the claimant is totally disabled by a respiratory or pulmonary impairment; it raises the further rebuttable presumption that the totally disabling, impairment results from pneumoconiosis, and that it arose from mine employment.
6. Upon invocation of the presumption under either one, or more, of (a)(l)-(4), the burden of persuasion is placed upon the employer to disprove by a preponderance of evidence any essential element of the claim that is only rebuttably presumed by reason of the claimant’s proof invoking the presumption. Thus, if the presumption was invoked under (a)(1) (X-ray or biopsy evidence) the employer may only rebut the presumption by proving by a preponderance of the evidence that the conclusively established pneumoconiosis did not arise out of mine employment or was not totally disabling within the statutory meaning.
If the presumption was invoked under (a)(2) or (a)(3), the employer may rebut it by proving by a preponderance of the evidence that the claimant’s clinically established impairment does not result from pneumoconiosis, or that if it does, the pneumoconiosis did not arise from mine employment or is not totally disabling.
If the presumption was invoked under (a)(4), the employer may rebut it by proving by a preponderance of the evidence that conclusively established totally disabling respiratory or pulmonary impairment is not pneumoconiosis, or that if it is, it did not arise from mine employment.
In any event, a single negative X-ray may not be relied upon as the sole basis for finding the presumption rebutted by disproving the presumed existence of pneumoconiosis. 30 U.S.C. § 923(b).
7. If the employer fails to carry the burden of persuasion in rebuttal by the available means, the claimant is entitled to benefits by virtue of the unrebutted presumption.
VI
Applying the presumption in this way to the appeals before us, I would decide them as follows.
A
Stapleton. I would affirm the denial of benefits though not on the basis relied upon by the majority.
The ALJ improperly found the presumption invoked by virtue of the single positive X-ray reading, without considering the several negative X-rays. The Benefits Review Board, however, properly upheld the denial of benefits on the alternative ground that the presumption should not have been found invoked under (a)(1) by reason of the negative X-ray evidence, or that if invoked under (a)(2) or (a)(4) it was sufficiently rebutted by medical testimony establishing that claimant’s impairment was cardiac in origin.
B
Ray. I would affirm the denial of benefits.
The ALJ’s determination that the presumption was not invoked under (a)(1) because of the overwhelming weight of seven “B” readers’ negative readings in relation to one unidentified reader’s positive reading and another’s reading only of “suspicious for early pneumoconiosis” is supported by substantial evidence.
Similarly, the AU’s determinations that, on conflicting test results, the presumption *449was not invoked under (a)(2), and that on conflicting medical opinion, it was not invoked under (a)(4), are also supported by substantial evidence.
C
Cornett. 'I would affirm the award of benefits but remand for calculation of interest.
The ALJ’s finding that the presumption was invoked under (a)(1) on conflicting X-ray readings is dubious. However, the finding that the presumption was invoked under (a)(2) by qualifying and near-qualifying blood gas studies, notwithstanding the evidence of non-qualifying results, cannot be reversed for lack of substantial evidence. Neither may we reverse for lack of substantial evidence the finding that, on conflicting medical testimony as to the degree of disability and as to its source, the presumption of total disability .from pneumoconiosis was not rebutted.
I am authorized to say that DONALD RUSSELL, MURNAGHAN, and ERVIN, JJ., join in this opinion.
. The relevant agency interpretation is that formally represented to us on these appeals by the Director, Office of Workers’ Compensation Programs who, as administrator of the Black Lung program by delegation of the Secretary of Labor, is authorized to make the agency interpretation. See 20 C.F.R. §§ 701.201, .202 (1979). The Director is before the court as a formal party by permitted intervention in these appeals, for the stated purpose of defending that interpretation.
Judge Sprouse fairly makes the point that agency interpretations advanced, as here, as litigation positions may be the least weighty type so far as judicial deference is concerned. Nevertheless, the one before us is given us as the official interpretation by the agency head. It is the only one we have. We effectively invited it from an interested agency not an original party to the actions. We have no indication that this interpretation, though advanced in specific litigation, is not the agency’s general position, nor that it is not "consistently applied” by the agency .in its base-line administration of the regulation.
. A critical reason for the principle of deference to an agency’s interpretation of its own regulations — aside from the obvious fact of authorship — is to encourage national uniformity of application. Given the range of arguably reasonable interpretations that are possible with respect to the details of a regulation such as that here in issue, the principle is particularly compelling here. Faithful adherence to the principle simply does not permit courts to substitute their own possibly "better" views of what a regulation should have provided in order best to carry out congressional intent as divined by the courts. Among other unhappy consequences of that approach is the inevitable divergence of views and applications that will emerge in judicial interpretations from circuit to circuit. Only if courts confine their review of agency interpretations to holding them within the outer bounds of the range of reasonableness contemplated by the principle of deference can the principle’s aims be achieved. This necessarily requires courts sometimes to yield their possibly "better” judgments about what an agency should have written, or about how an agency should have interpreted what it, after all, has written.
. Where, as here, a presumption is to be applied by an administrative fact-finder (or a bench trial judge) rather than by a judge controlling a jury trial, its essential function is not to prescribe a rigid order of proof, but simply to dictate an orderly process of evidence assessment. A ready analogy is the process of applying the judicially created McDonnell Douglas presumption of discrimination in Title VII bench trials, as explained in Furnco Construction Co. v. Waters, 438 U.S. 567, 577, 98 S.Ct. 2943, 2949, 57 L.Ed.2d 957 (1978) ("merely a sensible, orderly way to evaluate the evidence”); see also McCormick on Evidence, § 344 n. 2 (3d ed. 1984).
. For simplicity’s sake, this discussion is confined to living miner's claims — those being the only ones technically before us on these appeals.
. Judge Hall’s analysis, p. 434 & n. 7, of this aspect of the Director’s interpretation simply, with all deference, mistakes its import. In no way does the Director’s interpretation make the "presumption,” as opposed to the "basic facts" of the presumption, "irrebuttable” in whole or in part, and thus in conflict with the statutory requirement that any presumption of this sort be rebuttable.
Judge Hall’s analysis seemingly fails to grasp that, as interpreted by the Director and as its text plainly contemplates, the presumption may be invoked under (a)(1) — (4) by the establishment (along with miner status and 10 years mine employment) of any one or more of four different "medical requirements.” As established, these then constitute the "basic facts" of the presumption, whose "presumed facts” then vary depending upon which of the "medical *442requirement” basic facts have been established. For example, if pneumoconiosis’ existence is established as a "basic fact” under (a)(1), its mine-relatedness and its totally disabling effect become the "presumed facts" of the presumption, and this combination of basic and presumed facts make out a prima facie claim of compensable black lung disability. Under any possible combination of basic and presumed facts arising under (a)(l)~(4) there will be some "presumed facts” subject to rebuttal under (b)(1) — (4). But only the "presumed facts” are rebuttable, not the "basic facts.” Thus, continuing the example, if pneumoconiosis' existence has been "established” as a basic fact under (a)(1), that fact may not be "rebutted” (as the "basic facts," once "proven,” of presumptions in general may not be), but the "presumed facts” of mine-relatedness and of total resulting disability may of course be rebutted under, respectively, (b)(3) (not mine-related) or (b)(1) or (b)(2) (not totally disabling).
The analysis in text of this opinion, using the word “unless,” which to Judge Hall suggests an irrebuttable operation, simply describes the interrelation between the particular basic facts as established under (a)(1) — (4) and the resulting presumed facts that remain rebuttable under one or more of (b)(1) — (4). That is, the existence of pneumoconiosis may be rebutted under (b)(4) unless that "fact" has been established as a basic fact under (a)(1); but in the latter case, the “presumption " yet remains rebuttable, by disproof of the "presumed facts” of mine-relatedness or of total resulting disability.
Ironically, it is Judge Hall’s interpretation that would make the presumption effectively irrebutable in some situations. See pp. 446-447, infra.
. This is the operative word in each of the invocation and rebuttal subsections of § 727.-203 except subsection § 727.203(a)(3) which inexplicably shifts to the word “demonstrate" in referring to proof by blood gas studies.
The Director’s related interpretation that the persuasion burden is one of proof by a preponderance of the evidence is at the least not plainly erroneous or inconsistent with the regulation’s text. In fact, it is unassailable. Quite typically, the regulation expresses no standard. In such a circumstance, the preponderance standard, as the usual one in civil litigation, is presumptively the proper one. Beyond that, as the Director points out, this is the standard dictated by the Administrative Procedure Act in the absence of any specific standard’s expression. 5 U.S.C. §§ 554, 559.
Judge Hall’s basic disagreement on this point, which the court majority must accept, apparently goes to whether a persuasion burden under any standard is borne by the claimant rather than to the nature of the standard. But Judge Hall concludes that the APA standard is inapplicable because “superseded” by the relevant Black Lung statutes and regulations. Pp. 434-435 & n. 8. No support is advanced for this cryptic "conclusion” of something akin to implied repeal of the APA provisions.
. But that is necessarily the interpretation of Judge Hall and a majority of the en banc court, when Judge Hall writes, at odds with the Director’s internally consistent interpretation, that the claimant’s burden to invoke the presumption is not one of persuasion by a preponderance of the evidence, but is merely one of “producing evidence which meets one of the medical requirements [of § 727.203(a)(l)-(4) ].” P. 436.
. Indeed, it derives ultimately from a statutory provision to the same express effect in 30 U.S.C. § 923(b).
. Judge Hall draws upon this statutory provision as support for an interpretation that negative X-ray readings may not be considered at all in assessing whether the presumption has been invoked under § 727.203(a)(1). To hold otherwise, he says, would "in some cases ... subvert the congressional intention” expressed in this provision. P. 436, n. 10.
With respect, this claims too wide an effect for the limitation. Unless it means something other than "a negative chest X-ray,” it does not compel a reading that negative X-rays in general may not be considered at this stage, but only that a single one may not defeat the claim either at this or any stage.
Under Judge Hall's apparent interpretation, negative X-rays simply have no place in assessing claims under the interim presumption when the triggering provision of § 727.213(a)(1) ("a chest [X-ray]") is considered in conjunction *445with the limitation on proof expressed in 30 U.S.C. § 923(b). This simply flics in the face of the obvious understanding, expressed in many ways in statutes and regulations and exemplified in practice, that negative X-ray readings may be introduced in evidence and considered in assessing claims under the interim presumption, subject only to the express limitation in 923(b).
. The disagreement on critical elements is not total. On the critical aspect of the nature of the employer’s burden of proof in rebuttal, the Director's interpretation is also that the burden is one of persuasion. This, of course, is the single most important aspect of the presumption so far as tipping the substantive balance is concerned. It insures a tremendous practical litigation advantage to claimants, given the narrow proffer of proof required to place this risk of nonpersuasion on employers.
. Critical to this aspect of Judge Hall’s interpretation, as now accepted by a majority of the en banc court, is its emphasis on the word "a" that appears in subsections (a)(1) and (a)(4) of the regulation. This is said necessarily to import that "one” X-ray (or biopsy or autopsy?) and "one” physician's opinion suffice to trigger the presumption (and to preclude consideration of any contrary "like-kind” evidence).
With all respect, the word "a” in these two contexts seems to me better explained as a careless imprecision than as a deliberate means of conveying the critical meaning ascribed to it by Judge Hall’s analysis. The regulation at large is no more a grammarian’s dream than it is a proceduralist’s. Inexplicable oddities of syntax abound: e.g., the one-time shift to the word "demonstrate” in place of "establish” in § 727.-203(a)(3); the ungrammatical abandonment of parallelism caused by intrusion of the word “which” in § 727.203(a)(3); the ambiguous placement of the "all relevant medical evidence” mandate in the regulation.
Interestingly, Judge Hall’s analysis has to abandon this literalist approach in order to bring the plural language of (a)(2) and (a)(3) (ventilatory and blood gas “studies”) into line with its single test interpretation. This is accomplished by reading the singular word "set” into those two provisions. P. 436.
In the final analysis, this all serves merely to illustrate the futility of trying to interpret this regulation by a pick-and-choose literalist approach. The word "a” is present both in § 727.203(a)(1) and (a)(4), and in 30 U.S.C. § 923(b), and cannot be read out of either. Looking to total context, the most rational interpretation is that "a” single positive X-ray (or physician's opinion) may, but need not necessarily, trigger the presumption under § 727.-203(a)(1) or (4), and that a single negative X-ray may never provide the sole basis either for finding the presumption not invoked or for finding it rebutted once invoked under 30 U.S.C. § 923(b). So, I think, should we interpret it. See Part V, infra.
. Sanati actually dealt directly only with the triggering effect of medical opinion under § 727.203(a)(4), but its analysis related more broadly to the operation of all the "triggering” provisions, (a)(l)-(4). Critically, and correctly in my judgment, Judge Widener’s conclusion for the panel majority was that the presumption can only be triggered under any of these subsections by a preponderance of the evidence, i.e., that conflicting "like-kind” evidence must be considered. See Sanati, 713 F.2d at 482.
With all respect, I think Judge Widener's retreat now from Sanati is not warranted, certainly not by the cryptic (indeed legally incomprehensible) comment by the Secretary that he thinks compels his retreat. See 466 n. 1. If this comment proves anything it is that it was intended by the Secretary that all like-kind medical evidence should be considered both in determining whether the presumption is invoked and whether it is rebutted.
. Aside from the fundamental point that this limitation on proof flies in the face of the statutory and regulatory mandate for consideration of "all relevant evidence," its exact meaning as expressed in Whicker seems to me so unclear that it is bound to produce great confusion in the adjudication of claims. Presumably it would spawn major inquiry into the exact extent that ventilatory and blood gas studies may have influenced medical opinions. The standard of "principal or exclusive” would seem unmanageable on any principled basis. Certainly it would provide a wider latitude for judicial review of particular determinations than can be healthy for either the administering agency or for the courts or, more importantly, for primary agency administration of the program as intended by Congress.