opinion: Mr. Justice Frankfurter
  delivered the opinion of the Court.
  Petitioner was convicted by a jury in the United States District Court for the Eastern District of Missouri on two counts. Count I charged a conspiracy to obstruct commerce by extorting money, and Count II charged the substantive offense of obstructing commerce by extortion, both crimes made punishable by the Hobbs Anti-Racketeering Act, 18 U. S. C. § 1951. Petitioner was sentenced to consecutive terms of twelve years on each count, but the sentence on Count II was suspended and replaced with a five-year probation to commence at the expiration of his sentence under Count I. On appeal, the conviction was affirmed, 223 F. 2d 171.
  Petitioner thereafter sought a correction of his sentence, invoking Rule 35 of the Federal Rules of Criminal Procedure as well as 28 U. S. C. § 2255. He claimed that the maximum penalty for obstructing interstate commerce under the Act by any means is twenty years and that Congress did not intend to subject individuals to two penalties. The District Court denied relief, holding that the Hobbs Act gave no indication of a departure from the usual rule that a conspiracy and the substantive crime which was its object may be cumulatively punished. 173 P. Supp. 98. The Court of Appeals for the Eighth Circuit affirmed this judgment, 274 F. 2d 601. Deeming the question raised by petitioner of sufficient importance, we brought the case here. 362 U. S. 939.
  Under the early common law, a conspiracy — which constituted a misdemeanor — was said to merge with the completed felony which was its object. See Commonwealth v. Kingsbury, 5 Mass. 106. This rule, however, was based upon significant procedural distinctions between misdemeanors and felonies. The defendant in a misdemeanor trial was entitled to counsel and a copy of the indictment; these advantages were unavailable on trial for a felony. King v. Westbeer, 1 Leach 12, 15, 168 Eng. Rep. 108, 110 (1739); see Clark and Marshall, Crimes, §2.03, n. 96 (6th ed.). Therefore no conviction was permitted of a constituent misdemeanor upon an indictment for the felony. When the substantive crime was also a misdemeanor, People v. Mather, 4 Wend. 229, 265 (N. Y.), or when the conspiracy was defined by statute as a felony, State v. Mayberry, 48 Me. 218, 238, merger did not obtain. As these common-law procedural niceties disappeared, the merger concept lost significance, and today it has been abandoned. Queen v. Button, 11 Q. B. 929, 116 Eng. Rep. 720; Pinkerton v. United States, 328 U. S. 640.
  Petitioner does not draw on this archaic law of merger. He argues that Congress by combining the conspiracy and the substantive offense in one provision, § 1951, manifested an intent not to punish commission of two offenses cumulatively. ■ Unlike the merger doctrine, petitioner’s position does not question that the Government could charge a conspiracy even when the substantive crime that was its object had been completed. His concern is with the punitive consequences of the choice thus open to the Government; it can indict for both or either offense, but, petitioner contends, it can punish only for one.
  The present Hobbs Act had as its antecedent the Anti-Racketeering Act of 1934. In view of this Court’s restrictive decision in United States v. Local 807, 315 U. S. 521 (1942), Congress, under the leadership of Representative Hobbs, sought to stiffen the 1934 legislation. After several unsuccessful attempts over a period of four years, a bill was passed in 1946 which deleted any reference to wages paid by an employer to an employee, on which the decision in Local 807 had relied. The 1934 Act was further invigorated by increasing the maximum penalty from ten to twenty years.
  Petitioner relies on numerous statements by members of Congress concerning the severity of the twenty-year penalty to illustrate that cumulative sentences were not contemplated. But the legislative history sheds no light whatever on whether the Congressmen were discussing the question of potential sentences under the whole bill or merely defending the maximum punishment under its specific sections. All the legislative talk only reiterates what the statute itself says — that the maximum penalty is twenty years.
  The distinctiveness between a substantive offense and a conspiracy to commit is a postulate of our law. “It has been long and consistently recognized by the Court that the commission of the substantive offense and a conspiracy to commit it are separate and distinct offenses.” Pinkerton v. United States, 328 U. S. 640, 643. See also Pereira v. United States, 347 U. S. 1, 11. Over the years, this distinction has been applied in various situations. For example, in Clune v. United States, 159 U. S. 590, the Court upheld a two-year sentence for conspiracy over the objection that the crime which was the object of the unlawful agreement could only be punished by a $100 fine. The same result was reached when, as in the present case, both offenses were described within the same statute. In Carter v. McClaughry, 183 U. S. 365, cumulative sentences for conspiracy to defraud and fraud were upheld. “Cumulative sentences,” the Court pronounced, “are not cumulative punishments, and a single sentence for several offences, in excess of that prescribed for one offence, may be authorized by statute.” 183 U. S., at 394.
  This settled principle derives from the reason of things in dealing with socially reprehensible conduct: collective criminal agreement — partnership in crime — presents a greater potential threat to the public than individual delicts. Concerted action both increases the likelihood that the criminal object will be successfully attained and decreases the probability that the individuals involved will depart from their path of criminality. Group association for criminal purposes often, if not normally, makes possible the attainment of ends more complex than those which one criminal could accomplish. Nor is the danger of a conspiratorial group limited to the particular end toward which it has embarked. Combination in crime makes more likely the commission of crimes unrelated to' the original purpose for which the group was formed. In sum, the danger which a conspiracy generates is not confined to the substantive offense which is the immediate aim of the enterprise.
  These considerations are the presuppositions of the separately defined crimes in § 1951. The punitive consequences that presumably flow from them must be placed in such context. Congress is, after all, not a body of laymen unfamiliar with the commonplaces of our law. This legislation was the formulation of the two Judiciary Committees, all of whom are lawyers, and the Congress is predominately a lawyers’ body. We attribute “to Congress a tacit purpose — in the absence of any inconsistent expression — to maintain a long-established distinction between offenses essentially different; a distinction whose practical importance in the criminal law is not easily overestimated.” United States v. Rabinowich, 238 U. S. 78, 88.
  These considerations are reinforced by a prior interpretation of the Sherman Act whose minor penalties influenced the enactment of the 1934 anti-racketeering legislation. In American Tobacco Co. v. United States, 328 U. S. 781, individual and corporate defendants were convicted, inter alia, of conspiracy to monopolize and monopolization, both made criminal by § 2. They were sentenced to a fine of $5,000, the maximum statutory penalty, on each of the counts. We affirmed these convictions on the basis of our past decisions in this field of law. 328 U. S., at 788-789. To dislodge such conventional consequences in the outlawing of two disparate offenses, conspiracy and substantive conduct, and effectuate a reversal of the settled interpretation we pronounced in American Tobacco would require specific language to the contrary. See also Albrecht v. United States, 273 U. S. 1, 11; Burton v. United States, 202 U. S. 344, 377.
  Petitioner argues that some of the other provisions of § 1951 seem to overlap and would not justify cumulative punishment for separate crimes. From this he deduces a congressional intent that the statute allows punishment for only one crime no matter how many separately outlawed offenses have been committed. These contentions raise problems of statutory interpretation not now here. That some of the substantive sections may be repetitive as being variants in phrasing of the same delict, or that petitioner could not be cumulatively punished for both an attempt to extort and a completed act of extortion, has no relevance to the legal consequences of two incontestably distinctive offenses, conspiracy and the completed crime that is its object. In the American Tobacco litigation it was decided that the attempt to monopolize, described in § 2 of the Sherman Act, merged with the completed monopolization, but this result did not qualify the holding that cumulative sentences for the conspiracy and the substantive crime, also contained within § 2, were demanded by the governing precepts of our law.
  Petitioner invokes “the rule of lenity” for decision in this case. But that “rule,” as is true of any guide to statutory construction, only serves as an aid for resolving an ambiguity; it is not to be used to beget one. “To rest upon a formula' is a slumber that, prolonged, means death.” Mr. Justice Holmes in Collected Legal Papers, p. 306. The rule comes into operation at the end of the process of construing what Congress has expressed, not at the beginning as an overriding consideration of being lenient to wrongdoers. That is not the function of the judiciary. In United States v. Universal C. I. T. Credit Corp., 344 U. S. 218; Bell v. United States, supra, and Ladner v. United States, 358 U. S. 169, the applicable statutory provisions were found to be unclear as to the appropriate unit of prosecution; accordingly, the rule of lenity was utilized, in javorem libertatis, to resolve the ambiguity. In Prince v. United States, 352 U. S. 322, and Heflin v. United States, 358 U. S. 415, the Court had to meet the problem whether various subsidiary provisions of the Federal Bank Robbery Act, 18 U. S. C. § 2113, which - punished entering with intent to commit robbery and possessing stolen property, merged when applied to a defendant who was also being prosecuted for the robbery itself. Again the rule of lenity served to resolve the doubt with which Congress faced the Court.
  Here we have no such dubieties within the statute itself. Unlike all of these cases, the problem before us does not involve the appropriate unit of prosecution— whether conduct constitutes one or several violations of a single statutory provision — nor is it an open question whether conspiracy and its substantive aim merge into a single offense. This is an ordinary case of a defendant convicted of violating two separate provisions of a statute, whereby Congress defined two historically distinctive crimes composed of differing components. If petitioner had committed two separate acts of extortion, no one would question that the crimes could be punished by consecutive sentences; the result seems no less clear in the present case. It was therefore within the discretion of the trial judge to fix separate sentences, even though Congress has seen fit to authorize for each of these two offenses what may seem to some to be harsh punishment.
  Affirmed.
  Section 1951 (a) is as follows:
  “Whoever in any way or degree obstructs, delays, or affects commerce or the movement of any article or commodity in commerce, by robbery or extortion or attempts or conspires so to do, or commits or threatens physical violence to any person or property in furtherance of a plan or purpose to do anything in violation of this section shall be fined not more than $10,000 or imprisoned not more than twenty years, or both.”
  The pertinent parts of the Hobbs Act Amendments of 1946, 60 Stat. 420, from which the 1948 codification was compiled, were as follows:
  “Sec. 2. Whoever in any way or degree obstructs, delays, or affects commerce, or the movement of any article or commodity in commerce, by robbery or extortion, shall be guilty of a felony.
  "Sec. 3. Whoever conspires with another or with others, or acts in concert with another or with others to do anything in violation of section 2 shall be guilty of a felony.
  “Sec. 4. Whoever attempts or participates in an attempt to do anything in violation of section 2 shall be guilty of a felony.
  “Sec. 5. Whoever commits or threatens physical violence to any person or property in furtherance of a plan or purpose to do anything in violation of section 2 shall be guilty of a felony.
  “Sec. 6. Whoever violates any section of this title shall, upon conviction thereof, be punished by imprisonment for not more than twenty years or by a fine of not more than $10,000, or both.”
  The Reviser’s Note to the 1948 Code states that “The words ‘attempts or conspires so to do’ were substituted for sections 3 and 4 of the 1946 act, ...”
  Petitioner was released from imprisonment in April 1960 and currently is on parole. Both parties and the courts below apparently have interpreted the probationary period for Count II to commence at the expiration of petitioner’s parole for Count I.
  Both courts below ruled that 28 U. S. C. § 2255 was not available since it would be premature to claim the “right to be released” from a sentence not yet served. Since, as the Government concedes, Rule 35 is available to correct an illegal sentence when the claim is based on the face of the indictment even if such claim had not been raised on direct appeal, Heflin v. United States, 358 U. S. 415, 418, 422, the applicability of § 2255 need not be considered.
  The original bill, S. 2248, 73d Cong., 2d Sess., did not contain any provision concerning conspiracy. (Of course, the general conspiracy statute, R-. S. § 5440, now 18 U. S. C. § 371, which then provided for a maximum two-year sentence, was available.) The bill made punishable by imprisonment from one to ninety-nine years acts of violence, extortion, and coercion which interfered with interstate commerce. 78 Cong. Rec. 11403. The purpose of the legislation was to provide for direct prosecution of large-scale racketeering, which formerly had been ineffectively attempted through the Sherman Act, which had a maximum penalty of one-year imprisonment or $5,000 fine. S. Rep. No. 532, 73d Cong., 2d Sess. p. 1. After the bill had passed the Senate, 78 Cong. Rec. 5735, some question was raised as to whether legitimate labor activity was not threatened by the statutory phraseology, 78 Cong. Rec. 5859, 10867, and provisos were suggested by the House Judiciary Committee in reporting the measure to the full body. H. R. Rep. No. 1833, 73d Cong., 2d Sess. The Committee, upon the suggestion of the Attorney General, further added a section making conspiracy to comipit any of the designated substantive violations punishable. Ibid. The amended bill was passed by the House substantially as reported except that the penalty was decreased to ten years or $10,000. 78 Cong. Rec. 11403. The House bill was summarily approved by the Senate. 78 Cong. Rec. 11482,
  A little over two months after the decision, H. R. 7067 was introduced by Representative Hobbs in the House of Representatives, 88 Cong. Rec. 4080, following Hearings before a Subcommittee of the Committee on the Judiciary, 77th Cong., 2d Sess. The bill was reported favorably out of committee, the only major change being the reduction of the proposed twenty-year maximum sentence to ten years. In discussing the various provisions, the report stated: “The objective of Title I is to prevent anyone from obstructing, delaying, or affecting commerce, or the movement of any article or commodity in commerce by robbery or extortion as defined in the bill. A conspiracy or attempt to do anything in violation of section 2 is likewise made punishable . . . .” H. R. Rep. No. 2176, 77th Cong., 2d Sess., p. 9. No further congressional action was taken on the bill.
  The following year, Representative Hobbs introduced H. R. 653 which was identical with his prior bill. This time the Committee did not amend the twenty-year penalty. H. R. Rep. No. 66, 78th Cong., 1st Sess. The measure passed the House, 89 Cong. Rec. 3230, but no action was taken in the Senate.
  In 1945 Representative Hobbs again introduced his amendment. H. R. 32, 79th Cong., 1st Sess. The measure was passed by both bodies, 91 Cong. Rec. 11922, 92 Cong. Rec. 7308. Both Committee reports again stated that “A conspiracy or attempt to do anything in violation of section 2 is likewise made punishable.” S. Rep. No. 1516, 79th Cong., 2d Sess.; H. R. Rep. No. 238, 79th Cong., 1st Sess., p. 9.
  The pertinent parts of the amendment, 60 Stat. 420, are set out in n. 1, supra.
  Typical excerpts on which petitioner relies are:
  “Mr. DelaNey. The fact of the matter is that this committee report was not unanimous. Also, in the committee it was indicated by those who favor this legislation that the legislation is too drastic, that the $10,000 fine and 20 years in jail is too drastic. They think a modified bill might be more in consonance with present-day thinking.” (89 Cong. Rec. 3162.)
  “Mr. Fish. ... I want to refer likewise to some of the excessive penalties. The penalties in this bill in my opinion are too severe — 20 years and $10,000 fine. When we reach this section of the bill there should be very careful consideration given to reducing both the extent of the imprisonment and fines.” (89 Cong. Rec. 3194.)
  “Mr. SPRINGER. May I ask my distinguished colleague on the Committee on the Judiciary if it is not a fact that under the provisions of this bill the question of penalty is left entirely discretionary with the court trying the case ? Under the provisions of this bill a person could be penalized to the extent of 1 year or less than 1 year or up to 20 years, all in the discretion of the court.
  “Mr. Celler. Or his sentence might be suspended. I agree with the gentleman. But why do we single out labor and impose even a possible penalty of 20 years?” (89 Cong. Rec. 3201.)
  “Mr. RoBsroN. . . . There is some objection to the penalties pre scribed in this bill for robbery and extortion. It has gone forth to the country that the penalty is 20 years. That is not a correct statement. The penalties range from 1 hour up to 20 years, according to the offense, and fines of $1 to $10,000. In other words, the 20 years and the $10,000 fine are the maximum.” (89 Cong. Rec. 3226.)
  “Mr. Fish. . . . When the bill was before the Rules Committee it seemed to me at that time that these penalties were excessive. Twenty years is just about as bad as a life sentence, and I want to give the House the opportunity to reduce it by cutting it in half. This applies to threats. A man may be sent to jail for 20 years merely for threatening extortion.” (89 Cong. Rec. 3229.)
  For a discussion of these problems of the law of conspiracy see Developments in the Law — Criminal Conspiracy, 72 Harv. L. Rev. 920, 922-925, 968-971.
  The Senate Report which accompanied the original 1934 legislation described the purpose of the Act by setting forth a memorandum received from the Justice Department:
  ". . . The nearest approach to prosecution of racketeers as such has been under the Sherman Antitrust Act. This act, however, was designed primarily to prevent and punish capitalistic combinations and monopolies, and because of the many limitations engrafted upon the act by interpretations of the courts, the act is not well suited for prosecution of persons who commit acts of violence, intimidation, and extortion. . . . Moreover, a violation of the Sherman Act is merely a misdemeanor, punishable by 1 year in jail plus $5,000 fine, which is not a sufficient penalty for the usual acts of violence and intimidation affecting interstate commerce.” S. Rep. No. 532, 73d Cong., 2d Sess., p. 1.
  Representative Céller, in arguing for a less severe penalty during the 1945 debates, said:
  “If you look at the antitrust penalties against employers you find that they are only $5,000 or 1 year in jail. This bill has direct relation to the antitrust laws, the Clayton Act.” 91 Cong. Rec. 11902.
  See also Representative Celler’s remarks during the 1943 debates, 89 Cong. Rec. 3201.
  “When Congress leaves to the Judiciary the task of imputing to Congress an undeclared will, the ambiguity should be resolved in favor of lenity.” Bell v. United States, 349 U. S. 81, 83.
  The most notable illustration of this is the General Conspiracy Statute, 18 U. S. C. § 371.