Mr. Justice Brennan
delivered the opinion of the Court.
The question here is whether federal magistrates are authorized to conduct evidentiary hearings in federal habeas corpus cases. In 1968, Congress enacted the Federal Magistrates Act, 28 U. S. C. §§ 631-639, to upgrade and expand the former United States commissioner system. The Act authorizes magistrates to exercise all powers formerly exercised by United States commissioners, and also, as a means of relieving the caseload burden of the federal district judges, empowers magistrates to try minor offenses when all parties consent, and to perform such additional duties assigned by the district court as are “not inconsistent with the Constitution and laws of the United States.” Pursuant to the Act, the Judges of the United States District Court for the Western District of Kentucky amended Local Rule 16 of that court to provide:
“In addition to submitting such other reports and recommendations as may be required concerning petitions for writs of habeas corpus from state prisoners the full-time Magistrate is directed to schedule and hear evidentiary matters deemed by the Magistrate to be necessary and proper in the determination of each such petition, and to report thereon with an appropriate recommendation for the disposition thereof to the District Judge having jurisdiction of the case. The Magistrate shall cause the testimony of such hearing to be recorded on suitable electronic sound recording equipment. He shall submit his proposed findings of fact and conclusions of law to the proper Judge for his consideration, copies of which shall be provided at that time to the petitioner and respondent, and the Magistrate shall expeditiously transmit the proceedings, including the recording of the testimony, to the proper District Judge. Upon written request of either party, filed within ten days from the date such is so transmitted to the District Judge having jurisdiction thereof, the District Judge shall proceed to hear the recording of the testimony given at the evidentiary hearing and give it de novo consideration.”
Respondent is a state prisoner whose petition for federal habeas corpus relief was assigned by the District Court to a full-time Magistrate for processing under the rule. The part of the rule challenged here is that which directs the full-time magistrate “to schedule and hear evidentiary matters [to be electronically recorded] deemed by the Magistrate to be necessary and proper in the determination of . . . such petition, and to report thereon with an appropriate recommendation for the disposition thereof to the District Judge [who] . . . [u]pon . . . request. . . shall proceed to hear the recording of the testimony . . . and give it de novo consideration.” The question is whether this portion of the rule is invalid because “inconsistent with the . . . laws of the United States” within the meaning of the Federal Magistrates Act, 28 U. S. C. § 636.(b), or because § 636 (b) itself should be construed to preclude district courts from assigning such duties to magistrates.
I
Respondent, Carl James Wedding, is a prisoner in the Kentucky State Penitentiary serving a life sentence imposed in 1949 by the Webster Circuit Court, Commonwealth of Kentucky, after a plea of guilty to a charge of willful murder. Wedding filed this petition for habeas corpus in 1971. After the Court of Appeals for the Sixth Circuit reversed the initial dismissal of his petition, 456 F. 2d 245 (1972), and remanded for an evidentiary hearing, the District Court invoked Local Rule 16 and assigned the case to a full-time Magistrate to hold the hearing. Wedding promptly moved that the Magistrate be disqualified and the hearing be reassigned to a District Judge, on the ground that the Federal Magistrates Act did not authorize district courts to assign to magistrates the duty to hold habeas corpus evidentiary hearings. When the District Court denied the motion, the Magistrate proceeded with the hearing, and electronically recorded all testimonial evidence as required by Local Rule 16. Thereafter, the Magistrate transmitted the recording of the testimony to the District Judge and submitted written findings of fact and conclusions of law recommending that the petition be dismissed.
Wedding moved that the District Court give the matter a de novo hearing. The District Judge's response was to listen, as authorized by Local Rule 16, to the recording of the hearing before the Magistrate. On this basis and the Magistrate's findings and conclusions, the District Court entered an order dismissing respondent’s petition.
On appeal, Wedding renewed his challenge to Local Rule 16, relying upon Holiday v. Johnston, 313 U. S. 342 (1941). Holiday was also a federal habeas corpus case. There, after determining that the petition for writ of habeas corpus alleged facts which, if proved, would entitle the petitioner to relief, the District Judge issued a writ compelling the respondent to produce the petitioner before a designated United States Commissioner. The Commissioner held an evidentiary hearing at which the petitioner testified and the respondent submitted the depositions of two witnesses. On the basis of the evidence received, the Commissioner made findings of fact and stated conclusions of law recommending that the writ be denied. After hearing oral argument on the Commissioner's report, the District Judge entered an order discharging the writ.
This Court reversed, holding that the factfinding procedure employed failed to conform to Congress' express command in the Habeas Corpus Act that “[t]he court, or justice, or judge shall proceed in a summary way to determine the facts of the case, by hearing the testimony and arguments, and thereupon to dispose of the party as law and justice require.” Rev. Stat. § 761, 28 U. S. C. §461 (1940 ed.) (emphasis added). The Court held that the statute plainly accords a prisoner the right of testifying before a judge, stating:
“One of the essential elements of the determination of the crucial facts is the weighing and appraising of the testimony. Plainly it was intended that the prisoner might invoke the exercise of this appraisal by the judge himself. We cannot say that an appraisal of the truth of the prisoner’s oral testimony by a master or commissioner is, in the light of the purpose and object of the proceeding, the equivalent of the judge’s own exercise of the function of the trier of the facts.
“The District Judge should himself have heard the prisoner’s testimony and, in the light of it and the other testimony, himself have found the facts and based his disposition of the cause upon his findings.” Holiday v. Johnston, supra, at 352, 353-354.
Wedding contended that neither the text nor legislative history of the Federal Magistrates Act evidences a congressional intent to overrule Holiday. The Court of Appeals agreed and accordingly “vacate[d] the judgment of dismissal and remand [ed] the case with instructions that the [District] Court itself hold an evidentiary hearing on [Wedding’s] constitutional claims.” 483 F. 2d 1131, 1137 (CA6 1973). We granted certiorari, 414 U. S. 1157 (1974). We affirm.
II
Under our constitutional framework, the “great constitutional privilege” of habeas corpus, Ex parte Bollman 4 Cranch 75, 95 (1807) (Marshall, C. J.), has historically provided “a prompt and efficacious remedy for whatever society deems to be intolerable restraints. Its root principle is that in a civilized society, government must always be accountable to the judiciary for a man’s imprisonment: if the imprisonment cannot be shown to conform with the fundamental requirements of law, the individual is entitled to his immediate release.” Fay v. Noia,, 372 U. S. 391, 401-402 (1963). More often than not, claims of unconstitutional detention turn upon the resolution of contested issues of fact. Accordingly, since the Judiciary Act of February 5, 1867, c. 28, § 1, 14 Stat. 385, Congress has expressly vested plenary power in the federal courts “for taking testimony and trying the facts anew in habeas hearings . ...” Fay v. Noia, supra, at 416. See also Townsend v. Sain, 372 U. S. 293, 312 (1963).
In connection with the 1948 revision and recodification of the Judicial Code, Rev. Stat. § 761, construed in Holiday, and other procedural provisions of the Habeas Corpus Act were consolidated into 28 U. S. C. § 2243. The pertinent portion covering habeas corpus evidentiary hearings provides that “[t]he court shall summarily hear and determine the facts, and dispose of the matter as law and justice require.” The Revisers thus deleted some words from Rev. Stat. § 761, but the Revisers’ Notes accompanying § 2243, together with the reports of the Committee of the Judiciary of the Senate, and of the House, make abundantly clear that the word changes and omissions in Rev. Stat. § 761 were intended only as changes in form.
Accordingly, the construction of § 2243 has been that given § 761 in Holiday. United States v. Hayman, 342 U. S. 205, 213 n. 16 (1952); Brown v. Allen, 344 U. S. 443, 462-463 (1953). The Court held in the latter case:
“A federal judge on a habeas corpus application is required to ‘summarily hear and determine the facts, and dispose of the matter as law and justice require,’ 28 U. S. C. § 2243. This has long been the law. R. S. § 761, old 28 U. S. C. § 461.” Ibid, (emphasis added).
Ill
Our inquiry is thus narrowed to the question whether the Federal Magistrates Act changed the requirement of § 2243 that federal judges personally conduct habeas corpus evidentiary hearings. Certainly nothing in the text or legislative history of the Magistrates Act suggests that Congress meant to change that requirement. Rather, both text and legislative history plainly reveal a congressional determination to retain the requirement. For, although the Act gives district judges broad authority to assign a wide range of duties to magistrates, Congress carefully circumscribed the permissible scope of assignment to only “such additional duties as are not inconsistent with the Constitution and laws of the United States.” 28 U. S. C. § 636 (b) (emphasis added). And in defining assignable duties, Congress decreed that the duty of holding evidentiary hearings was not assignable. This clearly emerges from the legislative history of subsection (3) of § 636 (b), which provides:
“(3) preliminary review of applications for post-trial relief made by individuals convicted of criminal offenses, and submission of a report and recommendations to facilitate the decision of the district judge having jurisdiction over the case as to whether there should be a hearing.” (Emphasis added.)
That legislative history reveals that the Judicial Conference of the United States objected to successive phrasings of subsection (b) (3) until it was phrased to make clear that the authority given district courts to assign duties to magistrates did not include authority to hold evi-dentiary hearings on applications for posttrial relief. The original draft of the subsection had proposed that magistrates’ duties include
“(3) preliminary consideration of applications for post-trial relief made by individuals convicted of criminal offenses.”
But because that language was susceptible of the interpretation that magistrates might conduct evidentiary hearings, the Judicial Conference of the United States objected to it. Accordingly, the subsection was rewritten to provide for
“(3) preliminary review of applications for post-trial relief made by individuals convicted of criminal offenses, and submission of a report and recommendations to facilitate the decision of the district judge having jurisdiction over the case ...
The Committee on the Administration of the Criminal Law of the Judicial Conference objected that the revision did not “make it clear that it is the judge’s responsibility to make the ultimate decisions and to hold hearings on such applications, rather than that of the magistrate.” The Committee therefore recommended the addition of the phrase “as to whether there should be a hearing” immediately following the word “case.” The proposed addition was made, and subsection (b) (3) in its present form was enacted. Thus, although § 636 (b) provides that “additional duties authorized by rule may include, but are not restricted to,” duties defined in subsection (b) (3), the legislative history of the subsection compels the conclusion that Congress made a deliberate choice to preclude district courts from assigning magistrates the duty to hold evidentiary hearings.
We conclude that, since § 2243 requires that the District Judge personally hold evidentiary hearings in federal habeas corpus cases, Local Rule 16, insofar as it authorizes the full-time magistrate to hold such hearings, is invalid because it is “inconsistent with the . . . laws of the United States” under §636 (b). We conclude further that the Rule is to that extent invalid because, as we construe § 636 (b), that section itself precludes district judges from assigning magistrates the duty of conducting evidentiary hearings. Review by magistrates of applications for post-trial relief is thus limited to review for the purpose of proposing, not holding, eviden-tiary hearings. In connection with the preliminary review whether or not to propose that the district judge hold an evidentiary hearing, we agree that magistrates may receive the state court record and all affidavits, stipulations, and other documents submitted by the parties. Magistrates are prohibited only from conducting the actual evidentiary hearings.
The invalidity of Local Rule 16 is not cured by its provision that the “District Judge shall proceed to hear the recording of the testimony given at the evidentiary hearing and give it de novo consideration.” Holiday reasoned that the command of § 761, now § 2243, was designed by Congress in recognition that “[o]ne of the essential elements of the determination of the crucial facts is the weighing and appraising of the testimony.” 313 U. S., at 352. “To experienced lawyers it is commonplace that the outcome of a lawsuit — and hence the vindication of legal rights — depends more often on how the factfinder appraises the facts than on a disputed construction of a statute or interpretation of a line of precedents. Thus the procedures by which the facts of the case are determined assume an importance fully as great as the validity of the substantive rule of law to be applied.” Speiser v. Randall, 357 U. S. 513, 520 (1958). Congress, Holiday held, “[p]lainly . . . intended that the prisoner might invoke . . . appraisal by the judge himself.” In that circumstance, we “cannot say that an appraisal of the truth of the prisoner’s oral testimony” based on listening to a recording of it, “is, in the light of the purpose and object of the proceeding, the equivalent of the judge’s own exercise of the function of the trier of the facts.” 313 U. S., at 352.
Affirmed.
Commissioners had been empowered by the Federal Rules of Criminal Procedure to give oaths (Rule 3); issue arrest warrants (Rule 4); conduct preliminary examinations of arrestees (Rule 5); issue subpoenas (Rule 17); issue warrants of removal to another district (Rule 40); and release defendants on bail (Rule 46). In addition, commissioners were authorized to try persons accused of petty offenses (defined by 18 U. S. C. § 1 (3) as crimes for which the penalty does not exceed imprisonment for six months or a fine of not more than $500 or both) committed within the confines of federal enclaves, 62 Stat. 830. In civil cases commissioners were limited to administering oaths and taking bail, acknowledgments, affidavits, and depositions. 62 Stat. 917.
Unlike the more restricted criminal trial jurisdiction of the former commissioners, see n. 1, supra, the authority of magistrates extends to minor offenses committed anywhere within the judicial district and includes crimes punishable by imprisonment not exceeding one year, or a fine of not more than $1,000, or both.
The Federal Magistrates Act, 28 U. S. C. § 636 (b), provides:
“(b) Any district court of the United States, by the concurrence of a majority of all the judges of such district court, may establish rules pursuant to which any full-time United States magistrate, or, where there is no full-time magistrate reasonably available, any part-time magistrate specially designated by the court, may be assigned within the territorial jurisdiction of such court such additional duties as are not inconsistent with the Constitution and laws of the United States. The additional duties authorized by rule may include, but are not restricted to—
“Í1) service as a special master in an appropriate civil action pursuant to the applicable provisions of this title and the Federal Rules of Civil Procedure for the United States district courts;
“(2) assistance to a district judge in the conduct of pretrial or discovery proceedings in civil or criminal actions; and
“(3) preliminary review of applications for posttrial relief made by individuals convicted of criminal offenses, and submission of a report and recommendations to facilitate the decision of the district judge having jurisdiction over the case as to whether there should be a hearing.”
We thus agree with the Court of Appeals that this case does not require resolution of the question whether Congress constitutionally may enact legislation vesting authority, pursuant to rule or order of court, in magistrates to hold evidentiary hearings on habeas corpus petitions. We indicate no views as to the validity of investing such authority in a magistrate or other officer “outside the pale of Article III of the Constitution.” 483 F. 2d 1131, 1133 n. 1 (CA6 1973).
The relevant portion of the Judiciary Act of February 5, 1867, c. 28, § 1, 14 Stat. 385, provides that the “court or judge shall proceed in a summary way to determine the facts of the case, by hearing testimony and the arguments of the parties interested, and if it shall appear that the petitioner is deprived of his or her liberty in contravention of the constitution or laws of the United States, he or she shall forthwith be discharged and set at liberty.”
62 Stat. 869.
S. Rep. No. 1559, 80th Cong., 2d Sess., 2 (1948).
H. R. Rep. No. 308, 80th Cong., 1st Sess., A178 (1947).
See also J. Moore, Commentary on the U. S. Judicial Code 436 n. 78 (1949); Payne v. Wingo, 442 F. 2d 1192, 1194 (CA6 1971).
Had any substantive change in the meaning of Rev. Stat. § 761, as construed in Holiday v. Johnston, been intended, the Revisers’ Notes would have called attention to the change. William W. Barron, the Chief Reviser of the Code, explained: “[N]o changes of law or policy will be presumed from changes of language in revision unless an intent to make such changes is clearly expressed. Mere changes of phraseology indicate no intent to work a change of meaning but merely an effort to state in clear and simpler terms the original meaning of the statute revised.” Barron, The Judicial Code 1948 Revision, 8 F. R. D. 439, 445-446. See also S. Rep. No. 1559, 80th Cong., 2d Sess., 2 (1948); H. R. Rep. No. 308, 80th Cong., 1st Sess., 7 (1947).
A full discussion of the legislative history of the Federal Magistrates Act will be found in TPO, Inc. v. McMillen, 460 F. 2d 348 (CA7 1972).
Where Congress gave magistrates authority to conduct hearings, the authority was express and circumscribed with procedural safeguards. Thus 28 U. S. C. § 636 (a) (3) gives magistrates jurisdiction to conduct trials for minor offenses, but 18 U. S. C. § 3401 provides that any person charged with a minor offense may elect to be tried by a district judge. Title 28 U. S. C. § 636 (b) (1) authorizes magistrates to serve as special masters — which frequently involves the conduct of hearings — but makes that service subject to the Federal Rules of Civil Procedure, which include the restrictions of Rule 53 (b) that “reference to a master shall be the exception and not the rule.” See Note, Developments in the Law — Federal Habeas Corpus, 83 Harv. L. Rev. 1038,1189 n. 229 (1970).
S. 3475, Federal Magistrates Act of 1966, 89th Cong., 2d Sess. (1966).
See the Report of the Committee on the Administration of the Criminal Law, adopted by the Judicial Conference in September 1966, reprinted in the Hearings on S. 3475 and S. 945 before the Subcommittee on Improvements in Judicial Machinery of the Senate Committee on the Judiciary, 89th Cong., 2d Sess. (1966) and 90th Cong., 1st Sess. (1967), pp. 241j, 241n.
See the Report of the Committee on the Administration of the Criminal Law, adopted by the Judicial Conference in March 1967, reprinted in the Hearings on S. 3475 and S. 945 before the Subcommittee on Improvements in Judicial Machinery of the Senate Committee on the Judiciary, 89th Cong., 2d Sess. (1966) and 90th Cong., 1st Sess. (1967), pp. 244, 245.
Ibid.
S. 945, Federal Magistrates Act of 1967, 90th Cong., 1st Sess. (1967).
See Shapiro, Federal Habeas Corpus: A Study in Massachusetts, 87 Harv. L. Rev. 321, 364r-365 (1973); Note, Developments in the Law — Federal Habeas Corpus, 83 Harv. L. Rev. 1038, 1188-1189 (1970).
“A qualified, experienced magistrate will, it is hoped, acquire an expertise in examining these [post-conviction review] applications and summarizing their important contents for the district judge, thereby facilitating his decisions. Law clerks are presently charged with this responsibility by many judges, but judges have noted that the normal 1-year clerkship does not afford law clerks the time or experience necessary to attain real efficiency in handling such applications.” S. Rep. No. 371, 90th Cong., 1st Sess., 26 (1967).
To the extent that O’Shea v. United, States, 491 F. 2d 774 (CA1 1974), and Noorlander v. Ciccone, 489 F. 2d 642 (CA8 1973), suggest that magistrates may also accept oral testimony, provided that each party has the right to a de novo hearing before the district judge, we disagree. Such a procedure is precluded by both § 2243 and §636 (b).
Since under § 636 (b) district judges may call upon magistrates to relieve them of most other details of the processing of habeas corpus applications, it does not appear that judges will be significantly overburdened by the requirement that they personally conduct evidentiary hearings. Indeed, data from the Administrative Office of the United States Courts indicate that very few habeas corpus cases ever reach the evidentiary hearing stage. In 1973, of the 10,800 prisoner petitions filed for habeas corpus or as 28 U. S. C. § 2255 motions to vacate sentence, less than 5%, or approximately 530, necessitated evidentiary hearings. See Report of the Director of the Administrative Office of United States Courts, Table C-2, p. 325, Table C-8, p. 383 (1973). When hearings were required, 88% were completed in one day or less. Id., at 383. Thus, among the 400 District Judges, the burden of evidentiary hearings averages less than 1.5 hearing days per judge per year. To the extent that the 80 active Senior District Judges also participate in habeas corpus cases, the hearing burden upon each district judge is further reduced.