with whom Justice Brennan, Justice Marshall, and Justice Stevens join, dissenting.
The Court holds that Congress rationally has denied a small monthly “comfort allowance” to otherwise eligible people solely because previously it rationally denied them Medicaid benefits. In my view, Congress thoughtlessly has applied *240a statutory classification developed to further legitimate goals of one welfare program to another welfare program serving entirely different needs. The result is an exclusion of wholly dependent people from minimal benefits, serving no Government interest. This irrational classification violates the equal protection component of the Due Process Clause of the Fifth Amendment.
I
The Supplemental Security Income (SSI) program is a comprehensive federal program of minimal cash welfare benefits for the indigent blind, aged, and disabled. 86 Stat. 1465, 42 U. S. C. § 1381 et seq. See generally Califano v. Aznavorian, 439 U. S. 170, 171 (1978). Section 1611 (e)(1)(A) of the Act, 42 U. S. C. § 1382 (e)(1)(A), operates to reduce substantially, to $25 per month, the SSI benefits available to otherwise eligible persons who reside in public institutions. The reason for this reduction of benefit is understandable:
“For these people most subsistence needs are met by the institution and full benefits are not needed. Some payment to these people, though, would be needed to enable them to purchase small comfort items not supplied by the institution.” H. R. Rep. No. 92-231, p. 150 (1971).
See also S. Rep. No. 92-1230, p. 386 (1972). This comfort allowance is provided to institution residents only if the qualified person resides in a public hospital or institution that receives Medicaid funds on his behalf. 42 U. S. C. § 1382 (e)(1)(B). Thus, no comfort allowance will be paid to an individual unless the form of institutionalized treatment he receives is compensable under the separate Medicaid program.
Appellees are indigent people disabled by mental illness, and thus otherwise are eligible for SSI payments under 42 U. S. C. §§ 1382c (a)(3)(A), (C). As residents of public mental institutions between the ages of 21 and 65, however, they are ineligible to receive Medicaid benefits for their *241treatment. § 1396a (a)(17)(B).1 For this reason, and none other, appellees may not receive the reduced monthly SSI payments available to inmates of other medical institutions, including patients in public medical hospitals and private mental institutions.2
The refusal to pay for treatment in public mental institutions has a lengthy history in the development of the federal medical assistance programs. See Legion v. Richardson, 354 F. Supp. 456 (SDNY), summarily aff’d sub nom. Legion v. Weinberger, 414 U. S. 1058 (1973). Initially, Congress broadly refused federal aid to individuals diagnosed as mentally ill, ch. 809, §§303 (a), 343 (a), 351, 64 Stat. 549, 554, 557-558. Subsequent enactments, however, have extended Medicaid coverage to treatment of mental illness in public or private medical hospitals or nursing homes, 42 U. S. C. §§ 1396d (a)(1), (4) (1976 ed. and Supp. Ill), and to treatment of mental illness of those under 21 and 65 or over in public mental institutions, §§ 1396d (a) (14), (16). Moreover, Congress has defined “public institution” not to include a publicly operated community residence center serving no more than 16 residents. § 1382 (e) (1) (C). Thus, federal medical benefits have been extended to the mentally ill for *242treatment in various contexts. The residual exclusion of large state institutions for the mentally ill from federal financial assistance rests on two related principles: States traditionally have assumed the burdens of administering this form of care, and the Federal Government has long distrusted the economic and therapeutic efficiency of large mental institutions. See S. Rep. No. 404, 89th Cong., 1st Sess., 20 (1965). See also 42 U. S. C. § 1396d (h)(1)(B) (persons under 21 receive Medicaid benefits for treatment in mental institutions only when standards of utility are met).
The legislative history of § 1611 (e) sheds no light on why Congress made the exclusion from reduced SSI benefits coextensive with the exclusion from Medicaid payments.3 The Secretary argues that Congress might rationally have concluded that the States have the primary responsibility for making payments of comfort allowances to appellees, because they already bear the responsibility for paying for their treatment. Brief for Appellant 27. In accepting this justification, the Court adds that whether the States do, ever have, or ever will provide this benefit to residents of large mental institutions is irrelevant to the rationality of Congress’ supposed judgment. Ante, at 237, n. 20.
II
A
Social and economic legislation that does not employ suspect classifications or impinge on fundamental rights must be upheld under the equal protection component of the Fifth Amendment when the legislative means are rationally related to a legitimate Government purpose. U. S. Railroad Retirement Bd. v. Fritz, 449 U. S. 166 (1980). See San Antonio In*243pendent School District v. Rodriguez, 411 U. S. 1, 17 (1973); Dandridge v. Williams, 397 U. S. 471 (1970). This simply-stated test holds two firmly established principles in tension. The Court must not substitute its view of wise or fair legislative policy for that of the duly elected representatives of the people, Vance v. Bradley, 440 U. S. 93, 109 (1979); Dandridge, supra, at 485-486, but the equal protection requirement does place a substantive limit on legislative power. At a minimum, the legislature cannot arbitrarily discriminate among citizens. E. g., Johnson v. Robison, 415 U. S. 361, 374-375 (1974); James v. Strange, 407 U. S. 128, 140 (1972); Weber v. Aetna Casualty & Surety Co., 406 U. S. 164, 175 (1972). Enforcing this prohibition while avoiding unwarranted incursions on the legislative power presents a difficult task. No bright line divides the merely foolish from the arbitrary law.4 Given this difficulty, legislation properly enjoys a presumption of rationality, which is particularly strong for welfare legislation where the apportionment of scarce benefits in accordance with complex criteria requires painful but unavoidable line-drawing. Mathews v. De Castro, 429 U. S. 181, 185 (1976).
The deference to which legislative accommodation of conflicting interests is entitled rests in part upon the principle that the political process of our majoritarian democracy responds to the wishes of the people. Accordingly, an important touchstone for equal protection review of statutes is how readily a policy can be discerned which the legislature in*244tended to serve. See, e. g., U. S. Dept. of Agriculture v. Moreno, 413 U. S. 528, 536-538 (1973); McGinnis v. Royster, 410 U. S. 263, 270 (1973). When a legitimate purpose for a statute appears in the legislative history or is implicit in the statutory scheme itself, a court has some assurance that the legislature has made a conscious policy choice. Our democratic system requires that legislation intended to serve a discernible purpose receive the most respectful deference. See Harris v. McRae, 448 U. S. 297 (1980); Maher v. Roe, 432 U. S. 464, 479 (1977); Weinberger v. Salfi, 422 U. S. 749 (1975). Yet, the question of whether a statutory classification discriminates arbitrarily cannot be divorced from whether it was enacted to serve an identifiable purpose. When a legislative purpose can be suggested only by the ingenuity of a government lawyer litigating the constitutionality of a statute, a reviewing court may be presented not so much with a legislative policy choice as its absence.5
In my view, the Court should receive with some skepticism post hoc hypotheses about legislative purpose, unsupported by the legislative history.6 When no indication of legislative *245purpose appears other than the current position of the Secretary, the Court should require that the classification bear a “fair and substantial relation” to the asserted purpose. See F. S. Royster Guano Co. v. Virginia, 253 U. S. 412, 415 (1920). This marginally more demanding scrutiny indirectly would test the plausibility of the tendered purpose, and preserve equal protection review as something more than “a mere tautological recognition of the fact that Congress did what it intended to do.” Fritz, supra, at 180 (Stevens, J., concurring in judgment).
B
Neither the structure of § 1611 nor its legislative history identifies or even suggests any policy plausibly intended to be served by denying appellees the small SSI allowance. As noted above, the only purpose identified in the House and Senate Reports is the irrelevant goal of depriving inmates of penal institutions of all benefits. See n. 3, supra. The structure of the statute offers no guidance as to purpose because § 1611 (e) is drawn in reference to the policies of Medicaid rather than to the policies of SSI. By mechanically applying the criteria developed for Medicaid, Congress appears to have avoided considering what criteria would be appropriate for deciding in which public institutions a person can reside and still be eligible for some SSI payment. The importation of eligibility criteria from one statute to another creates significant risks that irrational distinctions will be made between equally needy people. See U. S. Dept. of Agriculture v. Murry, 413 U. S. 508, 514 (1973); Medora v. Colautti, 602 F. 2d 1149 (CA3 1979).
The Secretary argues, and the Court agrees, that the exclusion “is rationally related to the legitimate legislative desire to avoid spending federal resources on behalf of individuals whose care and treatment are being fully provided for by state and local government units.” Brief for Appellant 27. The Secretary does not argue that appellees are not *246in present need of the comfort allowance; indeed, he concedes that “the statutory classification does not exclude [appellees] because they were thought to be less needy.” Id., at 32.7 Nor does the Secretary suggest that because a State provides health care and the necessities of life to inmates of mental hospitals, the State also will provide the inmate with a comfort allowance. Indeed, the probability that a State will pay a patient a comfort allowance does not increase when the Federal Government refuses to relieve it of part of the cost of the patient’s medical care. The Court apparently recognizes this, as it states that whether or not a State actually provides a comfort allowance is irrelevant. Ante, at 237, n. 20. Ap-pellees simply are denied a benefit provided to other institutionalized, disabled patients.
But, it is argued, Congress rationally could make the judgment that the States should bear the responsibility for any comfort allowance, because they already have the responsibility for providing treatment and minimal care. There is no logical link, however, between these two responsibilities. See U. S. Dept. of Agriculture v. Murry, supra. Residence in a public mental hospital is rationally related to whether the Congress should pay for the patient’s treatment. Legion v. Richardson, 354 F. Supp. 456 (SDNY), summarily aff’d sub nom. Legion v. Weinberger, 414 U. S. 1058 (1973). The judgment whether the Federal Government should subsidize care for the mentally ill in large public institutions involves difficult questions of medical and economic policy. Supra, at 241-242. But residence in a public mental institution, as opposed to residence in a state medical hospital or a private mental hospital, bears no relation to any policy of the SSI program. The monthly $25 allowance pays for small personal expenses, beyond the minimal care and treatment pro*247vided by Medicaid or “other programs.” H. R. Rep. No. 96-451, pt. 1, p. 153 (1979). If SSI pays a cash benefit relating to personal needs other than maintenance and medical care, it is irrelevant whether the State or the Federal Government is paying for the maintenance and medical care.; the patients’ need remains the same, the likelihood that the policies of SSI will be fulfilled remains the same.
I conclude that Congress had no rational reason for refusing to pay a comfort allowance to appellees, while paying it to numerous otherwise identically situated disabled indigents. This unexplained difference in treatment must have been a legislative oversight. I therefore dissent.
Other classes of institutionalized people denied the reduced SSI allowance include patients in tubercular institutions and prison inmates.
The Court too quickly dispatches the argument that § 1611 (e) classifies on the basis of mental illness. While it is true that not all mentally ill people are denied the benefit, and that some people denied the benefit are not mentally ill, it is inescapable that appellees are denied the benefit because they are patients in mental institutions. Only the mentally ill are treated in mental institutions. While I would agree that there is no indication that Congress intended to punish or slight the mentally ill, the history of Medicaid demonstrates Congress’ disinclination to involve the Federal Government in state treatment of mental illness in public institutions. See infra, at this page and 242. Because I find the classification irrational, I do not reach the question whether classifications drawn in part on the basis of mental health require heightened scrutiny as appellees suggest.
The only indication of congressional intent states: “No assistance benefits will be paid to an individual in a penal institution.” H. R. Rep. No. 92-231, p. 150 (1971). A mental hospital is not a penal institution. Neither the Secretary nor the Court argues that the exclusion of appellees from the comfort allowance rationally furthers this purpose.
The Court has employed numerous formulations for the “rational basis” test. U. S. Railroad Retirement Bd. v. Fritz, 449 U. S. 166, 176-177, n. 10 (1980). Members of the Court continue to hold divergent views on the clarity with which a legislative purpose must appear, see id., at 180-181 (Stevens, J., concurring in judgment); id., at 187-188 (Brennan, J., dissenting), and about the degree of deference afforded the legislature in suiting means to ends, compare Lindsley v. Natural Carbonic Gas Co., 220 U. S. 61, 78-79 (1911), with F. S. Royster Guano Co. v. Virginia, 253 U. S. 412, 415 (1920).
Congress’ failure to mate policy judgments can distort our system of separation of powers by encouraging other branches to make essentially legislative decisions. See Cannon v. University of Chicago, 441 U. S. 677, 743 (1979) (Powell, J., dissenting).
Some of our cases suggest that the actual purpose of a statute is irrelevant, Flemming v. Nestor, 363 U. S. 603, 612 (1960), and that the statute must be upheld “if any state of facts reasonably may be conceived to justify” its discrimination, McGowan v. Maryland, 366 U. S. 420, 426 (1961). Although these cases preserve an important caution, they do not describe the importance of actual legislative purpose in our analysis. We recognize that a legislative body rarely acts with a single mind and that compromises blur purpose. Therefore, it is appropriate to accord some deference to the executive’s view of legislative intent, as similarly we accord deference to the consistent construction of a statute by the administrative agency charged with its enforcement. E. g., Udall v. Tollman, 380 U. S. 1, 16 (1965). Ascertainment of actual purpose to the extent feasible, however, remains an essential step in equal protection.
This concession makes it difficult to accept the Court’s conclusion that Congress rationally could have decided that “Medicaid recipients in public institutions . . . are the most needy and the most deserving of the small monthly supplement.” Ante, at 239.