opinion: Mr. Justice Douglas
  delivered the opinion of the Court.
  These are seven cases in which petitioner sued to recover stock assessments from shareholders of the Banco Kentucky Co. They were started in 1936 in the Eastern District of Kentucky and were stayed by agreement while the principal case upon which these depended, Anderson v. Abbott, 321 U. S. 349, wended its way through the courts. In the latter case we sustained the liability of the shareholders of Banco for the stock assessment. That was in 1944. During the time Anderson v. Abbott was being litigated, the shareholders involved in the present litigation died and respondents became executors of their estates. Through no lack of diligence, petitioner failed to learn of these facts until more than two years later. Upon learning of them he promptly moved to revive the actions against the representatives of the decedents. The District Court, following Anderson v. Brady, 1 F. R. D. 589, denied the motions for revivor and granted motions of the executors to dismiss. The Circuit Court of Appeals affirmed by a divided vote. 153 F. 2d 685. The case is here on a petition for a writ of certiorari which we granted because the case presented an important problem in the construction of the Rules of Civil Procedure.
  The case involves a reconciliation of Rule 25 (a) and Rule 6 (b). So far as material here, Rule 25 (a) provides:
  “If a party dies and the claim is not thereby extinguished, the court within 2 years after the death may order substitution of the proper parties. If substitution is not so made, the action shall be dismissed as to the deceased party.”
  And the relevant part of Rule 6(b) reads:
  “When by these rules or by a notice given thereunder or by order of court an act is required or allowed to be done at or within a specified time, the court for cause shown may, at any time in its discretion . . . (2) upon motion permit the act to be done after the expiration of the specified period where the failure to act was the result of excusable neglect; but it may not enlarge the period for taking any action under Rule 59, except as stated in subdivision (c) thereof, or the period for taking an appeal as provided by law.”
  It is said that since by Rule 25 (a) substitution may be made within two years after the death of a party, substitution is, within the meaning of Rule 6 (b), an act “allowed” to be done “within a specified time” which the court may on a showing of “excusable neglect” permit to be done after the two-year period. That argument is reinforced by reliance on the provision in Rule 6 (b) which grants but two exceptions to the power of enlargement of time. Since Rule 25 (a) is not included in the exceptions, it is argued that the time allowed by that rule may be enlarged under Rule 6(b). And it is pointed out that the facts of the present cases establish that the failure of the receiver to act within the two-year period was the result of “excusable neglect,” thus giving the District Court discretion to allow the substitution under Rule 6 (b).
  We agree, however, with the Circuit Court of Appeals. Rule 25 (a) is based in part on 28 U. S. C. § 778, 42 Stat. 352, which limited the power of substitution to two years from the death of a party. And even within that two-year period substitution could not be made unless the executor or administrator was served “before final settlement and distribution of the estate.” That statute, like other statutes of limitations, was a statute of repose. It was designed to keep short the time within which actions might be revived so that the closing and distribution of estates might not be interminably delayed. That policy is reflected in Rule 25 (a). Even within the two-year period substitution is not a matter of right; the court “may” order substitution but it is under no duty to do so. Under the Rule, as under the statute, the settlement and distribution of the estate might be so far advanced as to warrant a denial of the motion for substitution within the two-year period. In contrast to the discretion of the court to order substitution within the two-year period is the provision of Rule 25 (a) that if substitution is not made within that time the action “shall be dismissed” as to the deceased. The word “shall” is ordinarily “the language of command.” Escoe v. Zerbst, 295 U. S. 490, 493. And when the same Rule uses both “may” and “shall,” the normal inference is that each is used in its usual sense — the one act being permissive, the other mandatory. See United States v. Thoman, 156 U.S. 353, 360.
  Thus, as stated by the Circuit Court of Appeals, Rule 25 (a) operates both as a statute of limitations upon re-vivor and as a mandate to the court to dismiss an action not revived within the two-year period. Rule 6 (b) relates to acts required or allowed to be done by parties to an action and permits the court to afford relief to a party for his failure to act within the prescribed time limits. There would be more force in petitioner’s argument if Rule 25 (a) had, without more, set a two-year period within which substitution might be made. But Rule 25 (a) does not stop there. It directs the court to dismiss the action if substitution has not been made within that time. That is action required of the court, not of a party. And Rule 6 (b) should not be construed to override an express direction of action to be taken by the court. See Wallace v. United States, 142 F. 2d 240, 244.
  Reasons of policy support this construction. It is, to be sure, stipulated that in five of the present cases the estate is “still open and undistributed”; in one it is “still open”; in another it has been distributed. At least where an estate is ready to be closed or where there has already been a distribution, revivor may work unfairness and be disruptive of orderly and expeditious administration of estates. But it is not enough to say that if Rule 6 (b) and Rule 25 (a) are construed to permit substitution after the two-year period, the court need not allow it where unfairness or prejudice would result. For the normal policy of a statute of limitations is to close the door — finally, not qualifiedly or conditionally. The federal law embodied in Rule 25 (a) has a direct impact on the probate of estates in the state courts. It should not be construed to be more disruptive of prompt and orderly probate administration in those courts than its language makes necessary.
  Affirmed.
  The Chief Justice and Mr. Justice Reed took no part in the consideration or decision of this case.
  Petitioner brought actions against approximately 5,000 shareholders scattered throughout the United States and some in foreign countries. During the progress of the litigation some changed their residences. And it was stipulated that petitioner, with a limited staff, could not during this time keep up with the changes of residence or deaths of defendants.
  Cf. Ainsworth v. Gill Glass & Fixture Co., 104 F. 2d 83, with Burke v. Canfield, 72 App. D. C. 127, 111 F. 2d 526, and Mutual Benefit Health & Accident Assn. v. Snyder, 109 F. 2d 469.
  See note 1, supra.
  But see Baltimore & Ohio R. Co. v. Joy, 173 U. S. 226; Winslow v. Domestic Engineering Co., 20 F. Supp. 578.
  And see H. Rep. No. 429, 67th Cong., 1st Sess., p. 2.