484 U.S. 29 (1987)


JUSTICE WHITE delivered the opinion of the Court.


    The issue for decision involves several aspects of when a federal court may refuse to enforce an arbitration award rendered under a collective-bargaining agreement.


    Misco, Inc., (Misco, or the Company) operates a paper converting ph. in Monroe, Louisiana. The Company is a party to a collective-bargaining agreement with the United Paperworkers International Union, AFL-CI and its union local (the Union); the agreement covers the production a maintenance employees at the plant. Under the agreement, the Company the Union may submit to arbitration any grievance that arises from the interpretation or application of its terms, and the arbitrator's decision is final a: binding upon the parties. The arbitrator's authority is limited to interpretation and application of the terms contained in the agreement itself. The agreement reserves to management the right to establish, amend, and enforce "rules and regulations regulating the discipline or discharge of employee and the procedures for imposing discipline. Such rules were to be posted and were to be in effect "until ruled on by grievance and arbitration procedure as to fairness and necessity." For about a decade, the Company's rules h listed as causes for discharge the bringing of intoxicants, narcotics, or co trolled substances on to plant property or consuming any of them there, well as reporting for work under the influence of such substances. At the time of the events involved in this case, the Company was very concerned about the use of drugs at the plant, especially among employees on the night shift.


    Islah Cooper, who worked on the night shift for Misco, was one of the employees covered by the collective bargaining agreement. He operated a slitter-rewinder machine, which uses sharp blades to cut rolling coils of paper. The arbitrator found that this machine is hazardous and had caused numerous injuries in recent years. Cooper had been reprimanded twice in a few months for deficient performance. On January 21, 1983, one day after the second reprimand, the police searched Cooper's house pursuant to a warrant, and a substantial amount of marijuana was found. Contemporaneously, a police officer was detailed to keep Cooper's car under observation at the Company's parking lot. At about 6:30 p.m., Cooper was seen walking in the parking lot during work hours with two other men. The three men entered Cooper's car momentarily, then walked to another car, a white Cutlass, and entered it. After the other two men later returned to the plant, Cooper was apprehended by police in the backseat of this car with marijuana smoke in the air and a lighted marijuana cigarette in the front-seat ashtray. The police also searched Cooper's car and found a plastic scales case and marijuana gleanings. Cooper was arrested and charged with marijuana possession.


    On January 24, Cooper told the Company that he had been arrested for possession of marijuana at his home; the Company did not learn of the marijuana cigarette in the white Cutlass until January 27. It then investigated and on February 7 discharged Cooper, asserting that in the circumstances, his presence in the Cutlass violated the rule against having drugs on the plant premises. Cooper filed a grievance protesting his discharge the same day, and the matter proceeded to arbitration. The Company was not aware until September 21, five days before the hearing before the arbitrator was scheduled, that marijuana had been found in Cooper's car. That fact did not become known to the Union until the hearing began. At the hearing it was stipulated that the issue was whether the Company had "just cause to discharge the Grievant under Rule II.F' and, "[if not, what if any should be the remedy."


    The arbitrator upheld the grievance and ordered the Company to reinstate Cooper with backpay and full seniority. . . . In particular, the arbitrator found that the Company failed to prove that the employee had possessed or used marijuana on company property: finding Cooper in the backseat of a car and a burning cigarette in the front seat ashtray was insufficient proof that Cooper was using or possessed marijuana on company property. The arbitrator refused to accept into evidence the fact that marijuana had been found in Cooper's car on company premises because the Company did not know of this fact when Cooper was discharged and therefore did not rely on it as a basis for the discharge.


    The Company filed suit in District Court, seeking to vacate the arbitration award on several grounds, one of which was that ordering reinstatement of Cooper, who had allegedly possessed marijuana on the plant premises, was contrary to public policy. The District Court agreed that the award must be set aside as contrary to public policy because it ran counter to general safety concerns that arise from the operation of dangerous machinery while under the influence of drugs, as well as to state criminal laws against drug possession. The Court of Appeals affirmed. . . . The court ruled that reinstatement would violate the public policy "against the operation of dangerous machinery by persons under the influence of drugs or alcohol." The arbitrator had found that Cooper was apprehended on company premises in an atmosphere of marijuana smoke in another's car and that marijuana was found in his own car on the company lot. These facts established that Cooper had violated the Company's rules and gave the company just cause to discharge him. The arbitrator did not reach this conclusion because of a "narrow focus on Cooper's procedural rights" that led him to ignore what he "knew was in fact true: that Cooper did bring marijuana onto his employer's premises." Even if the arbitrator had not known of this fact at the time he entered his award, "it is doubtful that the award should be enforced today in light of what is now known."


    Because the Courts of Appeals are divided on the question of when courts may set aside arbitration awards as contravening public policy, we granted the Union's petition for a writ of certiorari, and now reverse the judgment of the Court of Appeals.


    Because the parties have contracted to have disputes settled by an arbitrator chosen by them rather than by a judge, it is the arbitrator's view of the facts and of the meaning of the contract that they have agreed to accept. Courts thus do not sit to hear claims of factual or legal error by an arbitrator as an appellate court does in reviewing decisions of lower courts. To resolve disputes about the application of a collective-bargaining agreement, an arbitrator must find facts and a court may not reject those findings simply because it disagrees with them. The same is true of the arbitrator's interpretation of the contract. The arbitrator may not ignore the plain language of the contract; but the parties having authorized the arbitrator to give meaning to the language of the agreement, a court should not reject an award on the ground that the arbitrator misread the contract. So, too, where it is contemplated that the arbitrator will determine remedies for contract violations that he finds, courts have no authority to disagree with his honest judgment in that respect. If the courts were free to intervene on these grounds, the speedy resolution of grievances by private mechanisms would be greatly undermined. . . .


    The Company's position, simply put, is that the arbitrator committed grievous error in finding that the evidence was insufficient to prove that Cooper had possessed or used marijuana on company property. But the Court of Appeals, although it took a distinctly jaundiced view of the arbitrator's decision in this regard, was not free to refuse enforcement because it considered Cooper's presence in the white Cutlass, in the circumstances, to be ample proof that Rule Il. 1 was violated. No dishonesty is alleged; only improvident, even silly, fact finding is claimed. This is hardly sufficient basis for disregarding what the agent appointed by the parties determined to be the historical facts.


    . . [The Court of Appeals] held that the evidence of marijuana in Cooper's car required that the award be set aside because to reinstate a person who had brought drugs onto the property was contrary to the public policy "against the operation of dangerous machinery by persons under the influence of drugs or alcohol." We cannot affirm that judgment.


    A court's refusal to enforce an arbitrator's award under a collective-bargaining agreement because it is contrary to public policy is a specific application of the more general doctrine, rooted in the common law, that a court may refuse to enforce contracts that violate law or public policy. W. R. Grace & Co. v. Rubber Workers, 461 U.S. 757 (1983). That doctrine derives from the basic notion that no court will lend its aid to one who founds a cause of action upon an immoral or illegal act, and is further justified by the observation that the public's interests in confining the scope of private agreements to which it is not a party will go unrepresented unless the judiciary takes account of those interests when it considers whether to enforce such agreements. In the common law of contracts, this doctrine has served as the foundation for occasional exercises of judicial power to abrogate private agreements,


    In W. R. Grace, . . . our decision turned on our examination of whether the award created any explicit conflict with other "laws and legal precedents" rather than an assessment of "general considerations of supposed public interests." At the very least, an alleged public policy must be properly framed under the approach set out in W. R. Grace, and the violation of such a policy must be clearly shown if an award is not to be enforced.


    As we see it, the formulation of public policy set out by the Court of Appeals did not comply with the statement that such a policy must be "ascertained 'by reference to the laws and legal precedents and not from general considerations of supposed public interests.' " The Court of Appeals made no attempt to review existing laws and legal precedents in order to demonstrate that they establish a "well defined and dominant" policy against the operation of dangerous machinery while under the influence of drugs. Although certainly such a judgment is firmly rooted in common sense, we explicitly held in W. R. Grace that a formulation of public policy based only on "general considerations of supposed public interests" is not the sort that permits a court to set aside an arbitration award that was entered in accordance with a valid collective-bargaining agreement.


    Even if the Court of Appeals' formulation of public policy is to be accepted, no violation of that policy was clearly shown in this case. In pursuing its public policy inquiry, the Court of Appeals quite properly considered the established fact that traces of marijuana had been found in Cooper's car. Yet the assumed connection between the marijuana gleanings found in Cooper's car and Cooper's actual use of drugs in the workplace is tenuous at best and provides an insufficient basis for holding that his reinstatement would actually violate the public policy identified by the Court of Appeals "against the operation of dangerous machinery by persons under the influence of drugs or alcohol." A refusal to enforce an award must rest on more than speculation or assumption.


    In any event, it was inappropriate for the Court of Appeals itself to draw the necessary inference. To conclude from the fact that marijuana had been found in Cooper's car that Cooper had ever been or would be under the influence of marijuana while he was on the job and operating dangerous machinery is an exercise in fact finding about Cooper's use of drugs and his amenability to discipline, a task that exceeds the authority of a court asked to overturn an arbitration award . The parties did not bargain for the facts to be found by a court, but by an arbitrator chosen by them who had more opportunity to observe Cooper and to be familiar with the plant and its problems. . . .


The judgment of the Court of Appeals is reversed.