BARNHART, COMMISSIONER OF SOCIAL SECURITY v. WALTON

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212 OCTOBER TERM, 2001
Syllabus
BARNHART, COMMISSIONER OF SOCIAL SECURITY
v. WALTON
certiorari to the united states court of appeals for
the fourth circuit
No. 00–1937. Argued January 16, 2002—Decided March 27, 2002
The Social Security Act authorizes payment of Title II disability insurance
benefits and Title XVI Supplemental Security Income to individuals
who have an “inability to engage in any substantial gainful activity by
reason of any medically determinable . . . impairment . . . which has
lasted or can be expected to last for a continuous period of not less
than 12 months.” 42 U. S. C. § 423(d)(1)(A) (emphasis added); accord,
§ 1382c(a)(3)(A). The Social Security Administration (Agency) denied
benefits to respondent Walton, finding that his “inability” to engage in
substantial gainful activity lasted only 11 months. The District Court
affirmed, but the Fourth Circuit reversed, holding that the 12-month
duration requirement modifies “impairment” not “inability,” that the
statute leaves no doubt that no similar duration requirement relates to
an “inability,” and that therefore Walton was entitled to benefits despite
Agency regulations restricting them to those unable to work for 12
months. The court decided further that Walton qualified for benefits
because, prior to his return to work, his “inability” would have been
“expected” to last 12 months. It conceded that the Agency had made
Walton’s actual return to work within 12 months of his onset date and
before the Agency’s decision date determinative on this point, 20 CFR
§§ 404.1520(b), 1592(d)(2), but found that the regulations conflicted with
the statute. It noted that Walton’s work simply counted as part of a
9-month trial work period during which persons “entitled” to Title II
benefits may work without loss of benefits, 42 U. S. C. § 422(c).
Held: The Agency’s interpretations of the statute fall within its lawful
interpretative authority. Pp. 217–225.
(a) The Agency’s reading of the term “inability” is reasonable. The
statute requires both an “inability” to engage in any substantial gainful
activity and an “impairment” providing “reason” for the “inability,” add-
ing that the “impairment” must last or be expected to last not less than
12 months. The Agency has determined in both its formal regulations
and its interpretation of those regulations that the “inability” must last
the same amount of time. Courts grant considerable leeway to an
agency’s interpretation of its own regulations, and the Agency has prop-
erly interpreted its regulation here. Thus, this Court must decide

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Syllabus
(1) whether the statute unambiguously forbids that interpretation, and
if not, (2) whether the interpretation exceeds permissible bounds.
Chevron U. S. A. Inc. v. Natural Resources Defense Council, Inc., 467
U. S. 837, 843. First, the Act does not unambiguously forbid the regula-
tion. That the statute’s 12-month phrase modifies only “impairment”
shows only that the provision says nothing explicitly about the “inabili-
ty’s” duration. Such silence normally creates, but does not resolve, am-
biguity. Second, the Agency’s construction is permissible. It supplies
a duration requirement, which the statute demands, in a way that con-
sistently reconciles the statutory “impairment” and “inability” language.
The Agency’s regulations also reflect the Agency’s own longstanding
interpretation, which should be accorded particular deference, North
Haven Bd. of Ed. v. Bell, 456 U. S. 512, 522, n. 12. Finally, Congress
has frequently amended or reenacted the relevant provisions without
change. Walton’s claim that Title II’s 5-month waiting period for enti-
tlement protects against a claimant with a chronic, but only briefly dis-
abling, disease shows, at most, that the Agency could have chosen other
reasonable time periods. Moreover, Title XVI has no such period, yet
Walton offers no explanation why its identical definitional language
should be interpreted differently in a closely related context. Walton’s
argument that the Agency’s interpretation should be disregarded be-
cause its formal regulations were only recently enacted is also rejected.
E. g., Smiley v. Citibank (South Dakota), N. A., 517 U. S. 735, 741. And
the Agency’s longstanding interpretation is not automatically deprived
of the judicial deference otherwise its due because it was previously
reached through means less formal than notice-and-comment rule-
making. Chevron, supra, at 843. Pp. 217–222.
(b) Also consistent with the statute is the Agency’s regulation provid-
ing that “[y]ou are not entitled to a trial work period” if “you perform
work . . . within 12 months of the onset of the impairment . . . and before
the date of any . . . decision finding . . . you . . . disabled,” 20 CFR
§ 404.1592(d)(2) (emphasis added). The statute is ambiguous, and the
regulation treats a pre-Agency-decision actual return to work as if it
were determinative of the “can be expected to last” question. The stat-
ute’s complexity, the vast number of claims it engenders, and the conse-
quent need for agency expertise and administrative experience lead the
Court to read the statute as delegating to the Agency considerable
authority to fill in matters of detail related to its administration. See
Schweiker v. Gray Panthers, 453 U. S. 34, 43–44. The interpretation
at issue is such a matter. Pp. 222–225.
235 F. 3d 184, reversed.

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214 BARNHART v. WALTON
Opinion of the Court
Breyer, J., delivered the opinion of the Court, Parts I and III of which
were unanimous, and Part II of which was joined by Rehnquist, C. J.,
and Stevens, O’Connor, Kennedy, Souter, Thomas, and Ginsburg,
JJ. Scalia, J., filed an opinion concurring in part and concurring in the
judgment, post, p. 226.
Jeffrey A. Lamken argued the cause for petitioner. With
him on the briefs were Solicitor General Olson, Assistant
Attorney General McCallum, Deputy Solicitor General
Kneedler, John C. Hoyle, and Mark S. Davies.
Kathryn L. Pryor argued the cause for respondent. With
her on the brief was James W. Speer.*
Justice Breyer delivered the opinion of the Court.
The Social Security Act authorizes payment of disability
insurance benefits and Supplemental Security Income to in-
dividuals with disabilities. See 49 Stat. 622, as amended, 42
U. S. C. § 401 et seq. (1994 ed. and Supp. V) (Title II disability
insurance benefits); § 1381 et seq. (Title XVI supplemental
security income). For both types of benefits the Act defines
the key term “disability” as an
“inability to engage in any substantial gainful activity
by reason of any medically determinable physical or
mental impairment which can be expected to result
in death or which has lasted or can be expected to last
for a continuous period of not less than 12 months.”
§ 423(d)(1)(A) (1994 ed.) (Title II) (emphasis added); ac-
cord, § 1382c(a)(3)(A) (1994 ed., Supp. V) (Title XVI).
This case presents two questions about the Social Security
Administration’s interpretation of this definition.
First, the Social Security Administration (which we shall
call the Agency) reads the term “inability” as including a “12
month” requirement. In its view, the “inability” (to engage
in any substantial gainful activity) must last, or must be ex-
*Rochelle Bobroff, Michael Schuster, and Robert E. Rains filed a brief
for AARP et al. as amici curiae urging affirmance.

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Opinion of the Court
pected to last, for at least 12 months. Second, the Agency
reads the term “expected to last” as applicable only when
the “inability” has not yet lasted 12 months. In the case of
a later Agency determination—where the “inability” did not
last 12 months—the Agency will automatically assume that
the claimant failed to meet the duration requirement. It
will not look back to decide hypothetically whether, despite
the claimant’s actual return to work before 12 months ex-
pired, the “inability” nonetheless might have been expected
to last that long.
The Court of Appeals for the Fourth Circuit held both
these interpretations of the statute unlawful. We hold, to
the contrary, that both fall within the Agency’s lawful inter-
pretive authority. See Chevron U. S. A. Inc. v. Natural Re-
sources Defense Council, Inc., 467 U. S. 837 (1984). Conse-
quently, we reverse.
I
In 1996 Cleveland Walton, the respondent, applied for both
Title II disability insurance benefits and Title XVI Supple-
mental Security Income. The Agency found that (1) by Oc-
tober 31, 1994, Walton had developed a serious mental illness
involving both schizophrenia and associated depression;
(2) the illness caused him then to lose his job as a full-time
teacher; (3) by mid-1995 he began to work again part time
as a cashier; and (4) by December 1995 he was working as a
cashier full time.
The Agency concluded that Walton’s mental illness had
prevented him from engaging in any significant work, i. e.,
from “engag[ing] in any substantial gainful activity,” for 11
months—from October 31, 1994 (when he lost his teaching
job) until the end of September 1995 (when he earned income
sufficient to rise to the level of “substantial gainful activity”).
See 20 CFR §§ 404.1574, 416.974 (2001). And because the
statute demanded an “inability to engage in any substantial
gainful activity” lasting 12, not 11, months, Walton was not
entitled to benefits.

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Opinion of the Court
Walton sought court review. The District Court affirmed
the Agency’s decision, but the Court of Appeals for the
Fourth Circuit reversed. Walton v. Apfel, 235 F. 3d 184,
186–187 (2000). The court said that the statute’s 12-month
duration requirement modifies the word “impairment,” not
the word “inability.” Id., at 189. It added that the stat-
ute’s “language . . . leaves no doubt” that there is no similar
“duration requirement” related to an “inability” (to engage
in substantial gainful activity). Ibid. It concluded that, be-
cause the statute’s language “speaks clearly” and is “unam-
biguous,” Walton was entitled to receive benefits despite
agency regulations restricting benefits to those unable to
work for a 12-month period. Ibid.
The court went on to decide that, in any event, Walton
qualified because, prior to Walton’s return to work, one
would have “expected” his “inability” to last 12 months. Id.,
at 189–190. It conceded that the Agency had made Walton’s
actual return to work determinative on this point. See 20
CFR §§ 404.1520(b), 1592(d)(2) (2001). But it found unlawful
the Agency regulations that gave the Agency the benefit of
hindsight—on the ground that they conflicted with the stat-
ute’s clear command. 235 F. 3d, at 190.
For either reason, the Fourth Circuit concluded, Walton
became “entitled” to Title II benefits no later than April
1995, five months after the onset of his illness. See 42
U. S. C. §§ 423(a)(1)(D)(i), 423(a)(1)(D)(ii) (providing for a
5-month “waiting period” before a claimant is “entitled” to
benefits), 423(c)(2)(A) (1994 ed.). It added that Walton’s
later work as a cashier was legally beside the point. That
work simply counted as part of a 9-month “trial work pe-
riod,” which the statute grants to those “entitled” to Title II
benefits, and which it permits them to perform without loss
of benefits. § 422(c).
The Government sought certiorari. It pointed out that
the Fourth Circuit’s first holding conflicts with those of other
Circuits, compare 235 F. 3d, at 189–190, with Titus v. Sulli-

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Opinion of the Court
van, 4 F. 3d 590, 594–595 (CA8 1993), and Alexander v. Rich-
ardson, 451 F. 2d 1185 (CA10 1971). It added that the
Fourth Circuit’s views were contrary to well-settled law and
would create additional Social Security costs of $80 billion
over 10 years. We granted the writ. We now reverse.
II
The statutory definition of “disability” has two parts.
First, it requires a certain kind of “inability,” namely, an “in-
ability to engage in any substantial gainful activity.” Sec-
ond, it requires an “impairment,” namely, a “physical or men-
tal impairment,” which provides “reason” for the “inability.”
The statute adds that the “impairment” must be one that
“has lasted or can be expected to last . . . not less than 12
months.” But what about the “inability”? Must it also last
(or be expected to last) for the same amount of time?
The Agency has answered this question in the affirmative.
Acting pursuant to statutory rulemaking authority, 42
U. S. C. §§ 405(a) (Title II), 1383(d)(1) (Title XVI), it has pro-
mulgated formal regulations that state that a claimant is not
disabled “regardless of [his] medical condition,” if he is doing
“substantial gainful activity.” 20 CFR § 404.1520(b) (2001).
And the Agency has interpreted this regulation to mean that
the claimant is not disabled if “within 12 months after the
onset of an impairment . . . the impairment no longer pre-
vents substantial gainful activity.” 65 Fed. Reg. 42774
(2000). Courts grant an agency’s interpretation of its own
regulations considerable legal leeway. Auer v. Robbins, 519
U. S. 452, 461 (1997); Udall v. Tallman, 380 U. S. 1, 16–17
(1965). And no one here denies that the Agency has prop-
erly interpreted its own regulation.
Consequently, the legal question before us is whether the
Agency’s interpretation of the statute is lawful. This Court
has previously said that, if the statute speaks clearly “to the
precise question at issue,” we “must give effect to the un-
ambiguously expressed intent of Congress.” Chevron, 467

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U. S., at 842–843. If, however, the statute “is silent or am-
biguous with respect to the specific issue,” we must sustain
the Agency’s interpretation if it is “based on a permissible
construction” of the Act. Id., at 843. Hence we must de-
cide (1) whether the statute unambiguously forbids the
Agency’s interpretation, and, if not, (2) whether the interpre-
tation, for other reasons, exceeds the bounds of the permissi-
ble. Ibid.; see also United States v. Mead Corp., 533 U. S.
218, 227 (2001).
First, the statute does not unambiguously forbid the regu-
lation. The Fourth Circuit believed the contrary primarily
for a linguistic reason. It pointed out that, linguistically
speaking, the statute’s “12-month” phrase modifies only the
word “impairment,” not the word “inability.” And to that
extent we agree. After all, the statute, in parallel phrasing,
uses the words “which can be expected to result in death.”
And that structurally parallel phrase makes sense in refer-
ence to an “impairment,” but makes no sense in reference to
the “inability.”
Nonetheless, this linguistic point is insufficient. It shows
that the particular statutory provision says nothing explic-
itly about the “inability’s” duration. But such silence, after
all, normally creates ambiguity. It does not resolve it.
Moreover, a nearby provision of the statute says that an
“individual shall be determined to be under a disability
only if his . . . impairment . . . [is] of such severity that
he is not only unable to do his previous work but
cannot . . . engage in any other kind of substantial gain-
ful work which exists in the national economy.” 42
U. S. C. § 423(d)(2)(A) (Title II); accord, § 1382c(a)(3)(B)
(Title XVI).
In other words, the statute, in the two provisions, specifies
that the “impairment” must last 12 months and also be se-
vere enough to prevent the claimant from engaging in virtu-
ally any “substantial gainful work.” The statute, we con-

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cede, nowhere explicitly says that the “impairment” must be
that severe (i. e., severe enough to prevent “substantial gain-
ful work”) for 12 months. But that is a fair inference from
the language. See Brief for AARP et al. as Amici Curiae
13 (conceding that an impairment must remain of “disabling
severity” for 12 months). At the very least the statute is
ambiguous in that respect. And, if so, then it is an equally
fair inference that the “inability” must last 12 months. That
is because the latter statement (i. e., that the claimant must
be unable to “engage in any substantial gainful activity” for
a year) is the virtual equivalent of the former statement
(i. e., that the “impairment” must remain severe enough to
prevent the claimant from engaging in “substantial gainful
work” for a year). It simply rephrases the same point in a
slightly different way.
Second, the Agency’s construction is “permissible.” The
interpretation makes considerable sense in terms of the stat-
ute’s basic objectives. The statute demands some duration
requirement. No one claims that the statute would permit
an individual with a chronic illness—say, high blood pres-
sure—to qualify for benefits if that illness, while itself lasting
for a year, were to permit a claimant to return to work after
only a week, or perhaps even a day, away from the job. The
Agency’s interpretation supplies a duration requirement,
which the statute demands, while doing so in a way that
consistently reconciles the statutory “impairment” and “in-
ability” language.
In addition, the Agency’s regulations reflect the Agency’s
own longstanding interpretation. See Social Security Rul-
ing 82–52, p. 106 (cum. ed. 1982) (“In considering ‘duration,’
it is the inability to engage in [substantial gainful activity]
that must last the required 12-month period”); Disability
Insurance State Manual § 316 (Sept. 9, 1965), Government
Lodging, Tab C, § 316 (“Duration of impairment refers to
that period of time during which an individual is continu-
ously unable to engage in substantial gainful activity because

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220 BARNHART v. WALTON
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of ” an impairment); OASI Disability Insurance Letter No. 39
(Jan. 22, 1957), id., Tab A, p. 1 (duration requirement refers
to the “expected duration of the medical impairment” at a
“level of severity sufficient to preclude” substantial gainful
activity”). And this Court will normally accord particular
deference to an agency interpretation of “longstanding” du-
ration. North Haven Bd. of Ed. v. Bell, 456 U. S. 512, 522,
n. 12 (1982).
Finally, Congress has frequently amended or reenacted
the relevant provisions without change. E. g., Social Secu-
rity Amendments of 1965, § 303(a)(1), 79 Stat. 366; see also
S. Rep. No. 404, 89th Cong., 1st Sess., pt. I, pp. 98–99 (1965)
(“[T]he committee’s bill . . . provide[s] for the payment of
disability benefits for an insured worker who has been or can
be expected to be totally disabled throughout a continuous
period of 12 calendar months” (emphasis added)); id., at 98
(rejecting effort to provide benefits to those with “short-
term, temporary disabilit[ies],” defined as inability to work
for six months); H. R. Rep. No. 92–231, p. 56 (1971) (“No ben-
efit is payable, however, unless the disability is expected to
last (or has lasted) at least 12 consecutive months” (emphasis
added)); S. Rep. No. 744, 90th Cong., 1st Sess., 49 (1967)
(“The committee also believes . . . that an individual who
does substantial gainful work despite an impairment or im-
pairments that otherwise might be considered disabling is
not disabled for purposes of establishing a period of disa-
bility”). These circumstances provide further evidence—if
more is needed—that Congress intended the Agency’s inter-
pretation, or at least understood the interpretation as statu-
torily permissible. Commodity Futures Trading Comm’n
v. Schor, 478 U. S. 833, 845–846 (1986).
Walton points in reply to Title II language stating that
a claimant who is “under a disability . . . shall be entitled
to a . . . benefit . . . beginning with the first month
after” a “waiting period” of “five consecutive calendar
months . . . throughout which” he “has been under a disa-

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bility.” 42 U. S. C. §§ 423(a)(1)(D)(i), 423(c)(2)(A). He adds
that this 5-month “waiting period” assures a lengthy period
of time during which the applicant (who must be “under a
disability” throughout) has been unable to work. And it
thereby provides ironclad protection against the claimant
who suffers a chronic, but only briefly disabling, disease, such
as the claimant who suffers high blood pressure in our earlier
example. See supra, at 219. This claim does not help Wal-
ton, however, for it shows, at most, that the Agency might
have chosen other reasonable time periods—a matter not
disputed. Regardless, Walton’s “waiting period” argument
could work only in respect to Title II, not Title XVI. Title
XVI has no waiting period, though it uses identical defini-
tional language. And Walton does not explain why we
should interpret the same statutory words differently in
closely related contexts. See Department of Revenue of
Ore. v. ACF Industries, Inc., 510 U. S. 332, 342 (1994)
(“ ‘[I]dentical words used in different parts of the same act
are intended to have the same meaning’ ” (quoting Sorenson
v. Secretary of Treasury, 475 U. S. 851, 860 (1986) (some in-
ternal quotation marks omitted)).
Walton also asks us to disregard the Agency’s interpreta-
tion of its formal regulations on the ground that the Agency
only recently enacted those regulations, perhaps in response
to this litigation. We have previously rejected similar argu-
ments. Smiley v. Citibank (South Dakota), N. A., 517 U. S.
735, 741 (1996); United States v. Morton, 467 U. S. 822, 835–
836, n. 21 (1984).
Regardless, the Agency’s interpretation is one of long
standing. See supra, at 220. And the fact that the Agency
previously reached its interpretation through means less for-
mal than “notice and comment” rulemaking, see 5 U. S. C.
§ 553, does not automatically deprive that interpretation of
the judicial deference otherwise its due. Cf. Chevron, 467
U. S., at 843 (stating, without delineation of means, that the
“ ‘power of an administrative agency to administer a congres-

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222 BARNHART v. WALTON
Opinion of the Court
sionally created . . . program necessarily requires the formu-
lation of policy’ ” (quoting Morton v. Ruiz, 415 U. S. 199, 231
(1974))). If this Court’s opinion in Christensen v. Harris
County, 529 U. S. 576 (2000), suggested an absolute rule to
the contrary, our later opinion in United States v. Mead
Corp., 533 U. S. 218 (2001), denied the suggestion. Id., at
230–231 (“[T]he want of ” notice and comment “does not de-
cide the case”). Indeed, Mead pointed to instances in which
the Court has applied Chevron deference to agency interpre-
tations that did not emerge out of notice-and-comment rule-
making. 533 U. S., at 230–231 (citing NationsBank of N. C.,
N. A. v. Variable Annuity Life Ins. Co., 513 U. S. 251, 256–
257 (1995)). It indicated that whether a court should give
such deference depends in significant part upon the interpre-
tive method used and the nature of the question at issue.
533 U. S., at 229–231. And it discussed at length why Chev-
ron did not require deference in the circumstances there
present—a discussion that would have been superfluous had
the presence or absence of notice-and-comment rulemaking
been dispositive. 533 U. S., at 231–234.
In this case, the interstitial nature of the legal question,
the related expertise of the Agency, the importance of
the question to administration of the statute, the complexity
of that administration, and the careful consideration the
Agency has given the question over a long period of time
all indicate that Chevron provides the appropriate legal lens
through which to view the legality of the Agency interpreta-
tion here at issue. See United States v. Mead Corp., supra;
cf. also 1 K. Davis & R. Pierce, Administrative Law Treatise
§§ 1.7, 3.3 (3d ed. 1994).
For these reasons, we find the Agency’s interpretation
lawful.
III
Walton’s second claim is more complex. For purposes of
making that claim, Walton assumes what we have just de-
cided, namely, that the statute’s “12 month” duration require-

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ments apply to both the “impairment” and the “inability” to
work requirements. Walton also concedes that he returned
to work after 11 months. But Walton claims that his work
from month 11 to month 12 does not count against him be-
cause it is part of a “trial work” period that the statute
grants to those “entitled” to Title II benefits. See 42
U. S. C. § 422(c). And Walton adds, he was “entitle[d]” to
benefits because—even though he returned to work after 11
months—his “impairment” and his “inability” to work were
nonetheless “expected to last” for at least “12 months” before
he returned to work.
To illustrate Walton’s argument, we simplify the actual cir-
cumstances. We imagine: (1) On January 1, Year One, Wal-
ton developed (a) a severe impairment, which (b) made him
unable to work; (2) Eleven (not twelve) months later, on De-
cember 1, Year One, Walton returned to work; (3) On July 1,
Year Two, the Agency adjudicated, and denied, Walton’s
claim for benefits. Walton argues that, even though he re-
turned to work after 11 months, had the Agency looked at
the matter, not ex post, but as if it were looking prior to his
return to work, the Agency would have had to conclude that
both his “impairment” and his “inability” to work “can be
expected to last for a continuous period of not less than 12
months.” § 423(d)(1)(A). He consequently satisfied the 12-
month duration requirement and became “entitled” to bene-
fits before he returned to work; he was in turn entitled to a
“trial work” period; and his subsequent work as a cashier,
being “trial work,” should not count against him.
The Agency’s regulations plainly reject this view of the
statute. They say, “You are not entitled to a trial work pe-
riod” if “you perform work . . . within 12 months of the onset
of the impairment(s) . . . and before the date of any notice of
determination or decision finding . . . you . . . disabled.” 20
CFR § 404.1592(d)(2) (2001). This regulation means that the
Agency, deciding before the end of Year One, might have
found that Walton’s impairment (or inability to work) “can

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224 BARNHART v. WALTON
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be expected to last” for 12 months. But the Agency, decid-
ing after Year One in which Walton in fact returned to
work, would not ask whether his impairment (or inability to
work) could have been expected to last 12 months.
The legal question is whether this Agency regulation is
consistent with the statute. The Court of Appeals, accept-
ing Walton’s view, concluded that it is not. It said that the
Agency’s rules—permitting the use of hindsight when re-
viewing claims—are inconsistent with the statute’s plain
language, 235 F. 3d, at 191. And, here, other courts have
agreed. See Salamalekis v. Commissioner of Soc. Sec., 221
F. 3d 828 (CA6 2000); Newton v. Chater, 92 F. 3d 688 (CA8
1996); Walker v. Secretary of Health and Human Servs., 943
F. 2d 1257 (CA10 1991); McDonald v. Bowen, 818 F. 2d 559
(CA7 1986).
Nonetheless, we believe that Agency regulation is lawful.
See Chevron, supra, at 843. The statute is ambiguous. It
says nothing about how the Agency, when it adjudicates a
matter after Year One, is to treat an earlier return to work.
Its language “can be expected to last” 12 months, 42 U. S. C.
§ 423(d)(1)(A), simply does not say as of what time the law
measures the “expectation.” Indeed, from a linguistic per-
spective, the phrase “can be expected” foresees a decision-
maker who is looking into the future, not a decisionmaker
who is in the future, looking back into the past in order to see
what then “was,” “could be,” or “could have been” expected.
And read in context, the purpose of the phrase “can be ex-
pected to last” might be one of permitting the Agency to
award benefits before 12 months have expired, not one of
denying the Agency the benefit of hindsight. See 65 Fed.
Reg., at 42780; cf. also S. Rep. No. 404, at 99.
At the same time, the Agency’s regulation seems a reason-
able, hence permissible, interpretation of the statute. In ef-
fect it treats a pre-Agency-decision actual return to work,
e. g., Walton’s return in December Year One, as if it were
determinative of the expectation question. With Year
Two’s hindsight, Walton’s “inability” to work “can” not “be

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expected to last 12 months.” And use of that hindsight
avoids the need for the Year Two decisionmaker in effect to
answer a highly unwieldy question in what grammarians
might call the pluperfect future tense.
Of course, administrators and judges are capable of an-
swering hypothetical questions of this kind. But here the
question concerns what must be a contrary-to-fact specula-
tion about the future. It is a speculation that, however
often raised, would rarely prove easy to resolve. And the
statute’s purpose does not demand its resolution. Indeed,
one might ask why, other things being equal, a claimant who
returns to work too early ordinarily to qualify for benefits
nonetheless should qualify if, but only if, that return was a
kind of medical surprise. Of course, as Walton says, such
a rule would help encourage (or at least not discourage) a
claimant’s early return to work. See generally S. Rep.
No. 1856, 86th Cong., 2d Sess., 15–16 (1960). But the statute
does not demand that the Agency make of this desirable end
an overriding interpretive principle. And the Agency has
recognized and addressed the problem of work disincentives
in other ways. See, e. g., 20 CFR §§ 404.1574(c), 404.1575(d)
(2001).
The statute’s complexity, the vast number of claims that
it engenders, and the consequent need for agency expertise
and administrative experience lead us to read the statute
as delegating to the Agency considerable authority to fill
in, through interpretation, matters of detail related to its
administration. See Schweiker v. Gray Panthers, 453 U. S.
34, 43–44 (1981). The interpretation at issue here is such
a matter. The statute’s language is ambiguous. And the
Agency’s interpretation is reasonable.
We conclude that the Agency’s regulation is lawful.
* * *
The judgment of the Fourth Circuit is
Reversed.

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226 BARNHART v. WALTON
Opinion of Scalia, J.
Justice Scalia, concurring in part and concurring in the
judgment.
I join all but Part II of the Court’s opinion.
I agree that deference is owed to regulations of the Social
Security Administration (SSA) interpreting the definition of
“disability,” 42 U. S. C. §§ 423(d)(1)(A), 1382c(a)(3)(A) (1994
ed. and Supp. V). See 65 Fed. Reg. 42774 (2000). As the
Court acknowledges, the recency of these regulations is
irrelevant, see ante, at 220–221 (citing Smiley v. Citibank
(South Dakota), N. A., 517 U. S. 735, 741 (1996); United
States v. Morton, 467 U. S. 822, 835–836, n. 21 (1984)).
I would therefore not go on, as the Court does, ante, at 219–
222, to address the SSA’s prior interpretation of the defini-
tion of “disability” in a 1982 Social Security Ruling, a 1965
Disability Insurance State Manual, and a 1957 OASI Disabil-
ity Insurance Letter.
I do not believe, to begin with, that “particular deference”
is owed “to an agency interpretation of ‘longstanding’ dura-
tion,” ante, at 220. That notion is an anachronism—a relic
of the pre-Chevron days, when there was thought to be only
one “correct” interpretation of a statutory text. A “long-
standing” agency interpretation, particularly one that dated
back to the very origins of the statute, was more likely
to reflect the single correct meaning. See, e. g., Watt v.
Alaska, 451 U. S. 259, 272–273 (1981). But once it is ac-
cepted, as it was in Chevron, that there is a range of permis-
sible interpretations, and that the agency is free to move
from one to another, so long as the most recent interpreta-
tion is reasonable its antiquity should make no difference.
Cf. Rust v. Sullivan, 500 U. S. 173, 186–187 (1991); Chevron
U. S. A. Inc. v. Natural Resources Defense Council, Inc., 467
U. S. 837, 863–864 (1984).
If, however, the Court does wish to credit the SSA’s earlier
interpretations—both for the purpose of giving the agency’s
position “particular deference” and for the purpose of relying
upon congressional reenactment with presumed knowledge

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Opinion of Scalia, J.
of the agency position, see ante, at 219–220—then I think the
Court should state why those interpretations were authori-
tative enough (or whatever-else-enough Mead requires) to
qualify for deference. See United States v. Mead Corp., 533
U. S. 218 (2001). I of course agree that more than notice-
and-comment rulemaking qualifies, see ante, at 221–222, but
that concession alone does not validate the Social Security
Ruling, the Disability Insurance State Manual, and the OASI
Disability Insurance Letter. (Only the latter two, I might
point out, antedate the congressional reenactments upon
which the Court relies.)
The SSA’s recently enacted regulations emerged from
notice-and-comment rulemaking and merit deference. No
more need be said.