Mr. Justice Black
delivered the opinion of the Court.
The principal question presented is whether the plaintiffs in this private antitrust action were barred from recovery by a doctrine known by the Latin phrase in pari delicto, which literally means “of equal fault.” The plaintiffs, petitioners here, were all dealers who had operated “Midas Muffler Shops” under sales agreements granted by respondent Midas, Inc. Their complaint charged that Midas had entered into a conspiracy with the other named defendants — its parent corporation International Parts Corp., two other subsidiaries, and six individual defendants who were officers or agents of the corporations — to restrain and substantially lessen competition in violation of § 1 of the Sherman Act and § 3 of the Clayton Act. They also charged that the defendants had violated § 2 (a) of the Clayton Act, as amended by the Robinson-Patman Act, by granting discriminations in prices and services to some of their customers without offering the same advantages to the plaintiffs. The District Court entered summary judgment for respondents with respect to all of petitioners’ claims. On appeal the Court of Appeals reversed the judgment for respondents on the Robinson-Patman claim but, over Judge Cummings’ dissent, affirmed the District Court’s ruling that the other claims were barred by the doctine of in pari delicto. The court also held that petitioners’ Sherman Act claim was barred because Midas and International, while functioning as separate corporations, had a common ownership and therefore could cooperate without creating an illegal conspiracy. 376 F. 2d 692 (1967). Because these rulings by the Court of Appeals seemed to threaten the effectiveness of the private action as a vital means for enforcing the antitrust policy of the United States, we granted certiorari. 389 U. S. 1034 (1968). For reasons to be stated, we reverse.
The economic arrangements that led to this lawsuit have a long history. Respondent International Parts has been in the business of manufacturing automobile mufflers and other exhaust system parts since 1938. In 1955 the owners of International initiated a detailed plan for promoting the sale of mufflers by extensively advertising the “Midas” trade name and establishing a nationwide chain of dealers who would specialize in selling exhaust system equipment. Each prospective dealer was offered a sales agreement prepared by Midas, Inc., a wholly owned subsidiary of International. The agreement obligated the dealer to purchase all his mufflers from Midas, to honor the Midas guarantee on mufflers sold by any dealer, and to sell the mufflers at resale prices fixed by Midas and at locations specified in the agreement. The dealers were also obligated to purchase all their exhaust system parts from Midas, to carry the complete line of Midas products, and in general to refrain from dealing with any of Midas’ competitors. In return Midas promised to underwrite the cost of the muffler guarantee and gave the dealer permission to use the registered trademark “Midas” and the service mark “Midas Muffler Shops.” The dealer was also granted the exclusive right to sell “Midas” products within his defined territory. He was not required to pay a franchise fee or to purchase or lease substantial capital equipment from Midas, and the agreement was cancelable by either party on 30 days’ notice.
Petitioners’ complaint challenged as illegal restraints of trade numerous provisions of the agreements, such as the terms barring them from purchasing from other sources of supply, preventing them from selling outside the designated territory, tying the sale of mufflers to the sale of other products in the Midas line, and requiring them to sell at fixed retail prices. Petitioners alleged that they had often requested Midas to eliminate these restrictions but that Midas had refused and had threatened to terminate their agreements if they failed to comply. Finally they alleged that one of the plaintiffs had had his agreement canceled by Midas for purchasing exhaust parts from a Midas competitor, and that the other plaintiff dealers had themselves canceled their agreements. All the plaintiffs claimed treble damages for the monetary loss they had suffered from having to abide by the restrictive provisions.
The Court of Appeals, agreeing with the District Court, held the suit barred because petitioners were in pari delicto. The court noted that each of the petitioners had enthusiastically sought to acquire a Midas franchise with full knowledge of these provisions and had “solemnly subscribed” to the agreement containing the restrictive terms. Petitioners had all made enormous profits as Midas dealers, had eagerly sought to acquire additional franchises, and had voluntarily entered into additional franchise agreements, all while fully aware of the restrictions they now challenge. Under these circumstances, the Court of Appeals concluded, “[i]t would be difficult, to visualize a case more appropriate for the application of the pan delicto doctrine.” 376 F. 2d, at 699.
We find ourselves in complete disagreement with the Court of Appeals. There is nothing in the language of the antitrust acts which indicates that Congress wanted to make the common-law in pari delicto doctrine a defense to treble-damage actions, and the facts of this case suggest no basis for applying such a doctrine even if it did exist. Although in pari delicto literally means “of equal fault,” the doctrine has been applied, correctly or incorrectly, in a wide variety of situations in which a plaintiff seeking damages or equitable relief is himself involved in some of the same sort of wrongdoing. We have often indicated the inappropriateness of invoking broad common-law barriers to relief where a private suit serves important public purposes. It was for this reason that we held in Kiefer-Stewart Co. v. Seagram & Sons, 340 U. S. 211 (1951), that a plaintiff in an antitrust suit could not be barred from recovery by proof that he had engaged in an unrelated conspiracy to commit some other antitrust violation. Similarly, in Simpson v. Union Oil Co., 377 U. S. 13 (1964), we held that a dealer whose consignment agreement was canceled for failure to adhere to a fixed resale price could bring suit under the antitrust laws even though by signing the agreement he had to that extent become a participant in the illegal, competition-destroying scheme. Both Simpson and Kiefer-Stewart were premised on a recognition that the purposes of the antitrust laws are best served by insuring that the private action will be an ever-present threat to deter anyone contemplating business behavior in violation of the antitrust laws. The plaintiff who reaps the reward of treble damages may be no less morally reprehensible than the defendant, but the law encourages his suit to further the overriding public policy in favor of competition. A more fastidious regard for the relative moral worth of the parties would only result in seriously undermining the usefulness of the private action as a bulwark of antitrust enforcement. And permitting the plaintiff to recover a windfall gain does not encourage continued violations by those in his position since they remain fully subject to civil and criminal penalties for their own illegal conduct. Kiefer-Stewart, supra.
In light of these considerations, we cannot accept the Court of Appeals’ idea that courts have power to undermine the antitrust acts by denying recovery to injured parties merely because they have participated to the extent of utilizing illegal arrangements formulated and carried out by others. Although petitioners may be subject to some criticism for having taken any part in respondents’ allegedly illegal scheme and for eagerly seeking more franchises and more profits, their participation was not voluntary in any meaningful sense. They sought the franchises enthusiastically but they did not actively seek each and every clause of the agreement. Rather, many of the clauses were quite clearly detrimental to their interests, and they alleged that they had continually objected to them. Petitioners apparently accepted many of these restraints solely because their acquiescence was necessary to obtain an otherwise attractive business opportunity. The argument that such conduct by petitioners defeats their right to sue is completely refuted by the following statement from Simpson: “The fact that a retailer can refuse to deal does not give the supplier immunity if the arrangement is one of those schemes condemned by the anti-trust laws.” 377 U. S., at 16. Moreover, even if petitioners actually favored and supported some of the other restrictions, they cannot be blamed for seeking to minimize the disadvantages of the agreement once they had been forced to accept its more onerous terms as a condition of doing business. The possible beneficial byproducts of a restriction from a plaintiff’s point of view can of course be taken into consideration in computing damages, but once it is shown that the plaintiff did not aggressively support and further the monopolistic scheme as a necessary part and parcel of it, his understandable attempts to make the best of a bad situation should not be a ground for completely denying him the right to recover which the antitrust acts give him. We therefore hold that the doctrine of in pari delicto, with its complex scope, contents, and effects, is not to be recognized as a defense to an antitrust action.
Respondents, however, seek to support the judgment below on a considerably narrower ground. They picture petitioners as actively supporting the entire restrictive program as such, participating in its formulation and encouraging its continuation. We need not decide, however, whether such truly complete involvement and participation in a monopolistic scheme could ever be a basis, wholly apart from the idea of in pari delicto, for barring a plaintiff’s cause of action, for in the present case the factual picture respondents attempt to paint is utterly refuted by the record. One of the restrictions which petitioners most strenuously challenge is the requirement that dealers purchase their supplies exclusively from Midas. Another is the requirement that dealers carry Midas’ full line of parts. Neither of these provisions could be in a dealer’s self-interest since they obligate him to buy from Midas regardless of whether more favorable prices can be-obtained from other sources of supply and regardless of whether he needs certain parts at all. In addition, the depositions refer to numerous instances in which petitioners asked Midas for permission to purchase from some other source of supply. The record shows that these requests were repeatedly refused by Midas representatives, who underscored the refusals by describing the very requests as “heresy” and by ■ commenting that dealers who bought from outside sources of supply were “asking for trouble” or “were going to be punished.” A Midas official warned petitioner Pierce, who had been buying some exhaust parts from other manufacturers, “Joe, this is just like cheating on your wife; it is grounds for divorce.”
These statements completely refute respondents’ argument that petitioners were active participants and show, to the contrary, that the illegal scheme was thrust upon them by Midas.
There remains for consideration only the Court of Appeals’ alternative holding that the Sherman Act claim should be dismissed because respondents were all part of a single business entity and were-therefore entitled to cooperate without creating an illegal conspiracy. But since respondents Midas and International availed themselves of the privilege of doing business through separate corporations, the fact of common ownership could not save them from any of the obligations that the law imposes on separate entities. See Timken Co. v. United States, 341 U. S. 593, 598 (1951); United States v. Yellow Cab Co., 332 U. S. 218, 227 (1947). In any event each petitioner can clearly charge a combination between Midas and himself, as of the day he unwillingly complied with the restrictive franchise agreements, Albrecht v. Herald Co., 390 U. S. 145, 150, n. 6 (1968); Simpson v. Union Oil Co., supra, or between Midas and other franchise dealers, whose acquiescence in Midas’ firmly enforced restraints was induced by “the communicated danger of termination,” United States v. Arnold, Schwinn & Co., 388 U. S. 365, 372 (1967); United States v. Parke, Davis & Co., 362 U. S. 29 (1960). Although respondents object that these particular theories of conspiracy now pressed by petitioners were not alleged with sufficient specificity in their complaint, this suggestion is completely without merit. Our modern rules provide for trying cases to serve the ends of justice and require that pleadings “be so construed as to do substantial justice.” Rule 8 (f), Fed. Rules Civ. Proc. The gist of petitioners’ cause of action has been clear from the outset, and respondents will in no way be prejudiced if petitioners are permitted to rely on these alternative theories of conspiracy.
It follows that the judgment of the Court of Appeals must be reversed. The case is remanded to that court with directions to reverse in full the judgment of the District Court and to remand the case for trial.
It is so ordered.
26 Stat. 209,15 ü. S. C. § 1.
38 Stat. 731,15 U. S. C. § 14.
49 Stat. 1526,15 U. S. C. § 13.
In their motion for summary judgment respondents also argued that the restraints were permissible as reasonable means to protect their registered trade and service marks, but because they had failed to answer interrogatories pertinent to this defense, the district judge ordered it stricken, without prejudice to renewal if respondents promptly answered the relevant interrogatories. Because of its disposition of the case, the Court of Appeals reached neither the merits of this defense nor the question whether respondents had ever properly renewed it. In the circumstances of this case, we think the merits of this defense cannot be decided as a summary judgment question but must be resolved, along with all the other issues, by a trial on the merits.
Respondents suggest that these requirements were beneficial to a dealer because they helped him win customers who had confidence in the “Midas” brand, and some dealers evidently did try to reap some benefit from these, requirements by advertising, “You get only nationally-advertised Midas products.” It seems highly unlikely, however, that benefits of this kind could do more than mitigate very slightly the losses that a dealer would suffer when forced to buy higher-priced Midas products, particularly since dealers would have bought the higher-priced Midas products voluntarily if they thought customer preferences for the brand would be sufficiently strong to offset the higher price.