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 [p. 588] Act, 18 U.S.C. s 1951, 18 U.S.C.A. s 1951. [n. 1] 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.
 

1. 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 thereafter sought a correction of his sentence, invoking Rule 35 of the Federal Rules of Criminal [p. 589] Procedure, 18 U.S.C.A., as well as 28 U.S.C. s 2255, 28 U.S.C.A. s 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 F.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, 80 S.Ct. 807, 4 L.Ed.2d 769.

 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, s 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., N.Y., 229, 265, 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 [p. 590] 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, 66 S.Ct. 1180, 90 L.Ed. 1489.

 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, s 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 [p. 591] decision in United States v. Local 807, 1942, 315 U.S. 521, 62 S.Ct. 642, 86 L.Ed. 1004, 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 [p. 592] 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 [p. 593] 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.  'If 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, 66 S.Ct. 1180, 1182, 90 L.Ed. 1489.  See also Pereira v. United States, 347 U.S. 1, 11, 74 S.Ct. 358, 364, 98 L.Ed. 435.  Over the years, this distinction has been applied in various situations. For example, in Clune v. United States, 159 U.S. 590, 16 S.Ct. 125, 40 L.Ed. 269, 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, 22 S.Ct. 181, 46 L.Ed. 236, 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 offenses, in excess of that prescribed for one offense, may be authorized to statute.' 183 U.S. at page 394, 22 S.Ct. at page 193.

 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 [p. 594] 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.

* * *

 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. [n. 9] '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, 73 S.Ct. 227, 97 L.Ed. 260; Bell v. United States, 349 U.S. 81, 75 S.Ct. 620, 99 L.Ed. 905, and Ladner v. United States, 358 U.S. 169, 79 S.Ct. 209, 3 L.Ed.2d 199, the applicable statutory provisions were found to be unclear as to the appropriate unit of prosecution; accordingly, the rule of lenity was utilized, in favorem libertatis, to resolve the ambiguity.  In Price v. United States, 352 U.S. 322, 77 S.Ct. 403, 1 L.Ed.2d 370, and Heflin v. United States, 358 U.S. 415, 79 S.Ct. 451, 3 L.Ed.2d 407, the Court had to meet the problem whether various subsidiary provisions of the Federal Bank Robbery Act, 18 U.S.C. s 2113, 18 U.S.C.A. s 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.
 

9. 'When Congress leaves to the Judiciary the task of imputing to Congress an undeclared will, the ambiquity should be resolved in favor of lenity.'  Bell v. United States, 349 U.S. 81, 83, 75 S.Ct. 620, 622, 99 L.Ed. 905.

 [p. 597] 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.