Justice GORSUCH delivered the opinion of the Court.
The Federal Arbitration Act requires courts to enforce private arbitration agreements. But like most laws, this one bears its qualifications. Among other things, § 1 says that nothing herein may be used to compel arbitration in disputes involving the contracts of employment of certain transportation workers. 9 U.S.C. § 1. And that qualification has sparked these questions: When a contract delegates questions of arbitrability to an arbitrator, must a court leave disputes over the application of § 1s exception for the arbitrator to resolve? And does the term contracts of employment refer only to contracts between employers and employees, or does it also reach contracts with independent contractors? Because courts across the country have disagreed on the answers to these questions, we took this case to resolve them.
I
New Prime is an interstate trucking company and Dominic Oliveira works as one of its drivers. But, at least on paper, Mr. Oliveira isnt an employee; the parties contracts label him an independent contractor. Those agreements also instruct that any disputes arising out of the parties relationship should be resolved by an arbitrator-even disputes over the scope of the arbitrators authority.
Eventually, of course, a dispute did arise. In a class action lawsuit in federal court, Mr. Oliveira argued that New Prime denies its drivers lawful wages. The company may call its drivers independent contractors. But, Mr. Oliveira alleged, in reality New Prime treats them as employees and fails to pay the statutorily due minimum wage. In response to Mr. Oliveiras complaint, New Prime asked the court to invoke its statutory authority under the Act and compel arbitration according to the terms found in the parties agreements.
That request led to more than a little litigation of its own. Even when the parties contracts mandate arbitration, Mr. Oliveira observed, the Act doesnt always authorize a court to enter an order compelling it. In particular, § 1 carves out from the Acts coverage contracts of employment of ... workers engaged in foreign or interstate commerce. And at least for purposes of this collateral dispute, Mr. Oliveira submitted, it doesnt matter whether you view him as an employee or independent contractor. Either way, his agreement to drive trucks for New Prime qualifies as a contract[ ] of employment of ... [a] worker[ ] engaged in ... interstate commerce. Accordingly, Mr. Oliveira argued, the Act supplied the district court with no authority to compel arbitration in this case.
Naturally, New Prime disagreed. Given the extraordinary breadth of the parties arbitration agreement, the company insisted that any question about § 1s application belonged for the arbitrator alone to resolve. Alternatively and assuming a court could address the question, New Prime contended that the term contracts of employment refers only to contracts that establish an employer-employee relationship. And because Mr. Oliveira is, in fact as well as form, an independent contractor, the company argued, § 1s exception doesnt apply; the rest of the statute does; and the district court was (once again) required to order arbitration.
Ultimately, the district court and the First Circuit sided with Mr. Oliveira. 857 F.3d 7 (2017). The court of appeals held, first, that in disputes like this a court should resolve whether the parties contract falls within the Acts ambit or § 1s exclusion before invoking the statutes authority to order arbitration. Second, the court of appeals held that § 1 s exclusion of certain contracts of employment removes from the Acts coverage not only employer-employee contracts but also contracts involving independent contractors. So under any account of the parties agreement in this case, the court held, it lacked authority under the Act to order arbitration.
II
In approaching the first question for ourselves, one thing becomes clear immediately. While a courts authority under the Arbitration Act to compel arbitration may be considerable, it isnt unconditional. If two parties agree to arbitrate future disputes between them and one side later seeks to evade the deal, §§ 3 and 4 of the Act often require a court to stay litigation and compel arbitration accord[ing to] the terms of the parties agreement. But this authority doesnt extend to all private contracts, no matter how emphatically they may express a preference for arbitration.
Instead, antecedent statutory provisions limit the scope of the courts powers under §§ 3 and 4. Section 2 provides that the Act applies only when the parties agreement to arbitrate is set forth as a written provision in any maritime transaction or a contract evidencing a transaction involving commerce. And § 1 helps define § 2s terms. Most relevant for our purposes, § 1 warns that nothing in the Act shall apply to contracts of employment of seamen, railroad employees, or any other class of workers engaged in foreign or interstate commerce. Why this very particular qualification? By the time it adopted the Arbitration Act in 1925, Congress had already prescribed alternative employment dispute resolution regimes for many transportation workers. And it seems Congress did not wish to unsettle those arrangements in favor of whatever arbitration procedures the parties private contracts might happen to contemplate. Circuit City Stores, Inc. v. Adams, 532 U.S. 105, 121, 121 S.Ct. 1302, 149 L.Ed.2d 234 (2001).
Given the statutes terms and sequencing, we agree with the First Circuit that a court should decide for itself whether § 1s contracts of employment exclusion applies before ordering arbitration. After all, to invoke its statutory powers under §§ 3 and 4 to stay litigation and compel arbitration according to a contracts terms, a court must first know whether the contract itself falls within or beyond the boundaries of §§ 1 and 2. The parties private agreement may be crystal clear and require arbitration of every question under the sun, but that does not necessarily mean the Act authorizes a court to stay litigation and send the parties to an arbitral forum.
Nothing in our holding on this score should come as a surprise. Weve long stressed the significance of the statutes sequencing. In Bernhardt v. Polygraphic Co. of America, 350 U.S. 198, 201-202, 76 S.Ct. 273, 100 L.Ed. 199 (1956), we recognized that Sections 1, 2, and 3 [and 4] are integral parts of a whole.... [Sections] 1 and 2 define the field in which Congress was legislating, and §§ 3 and 4 apply only to contracts covered by those provisions. In Circuit City, we acknowledged that Section 1 exempts from the [Act] ... contracts of employment of transportation workers. 532 U.S., at 119, 121 S.Ct. 1302. And in Southland Corp. v. Keating, 465 U.S. 1, 10-11, and n. 5, 104 S.Ct. 852, 79 L.Ed.2d 1 (1984), we noted that the enforceability of arbitration provisions under §§ 3 and 4 depends on whether those provisions are part of a written maritime contract or a contract evidencing a transaction involving commerce under § 2 -which, in turn, depends on the application of § 1s exception for certain contracts of employment.
To be sure, New Prime resists this straightforward understanding. The company argues that an arbitrator should resolve any dispute over § 1s application because of the delegation clause in the parties contract and what is sometimes called the severability principle. A delegation clause gives an arbitrator authority to decide even the initial question whether the parties dispute is subject to arbitration. Rent-A-Center, West, Inc. v. Jackson, 561 U.S. 63, 68-69, 130 S.Ct. 2772, 177 L.Ed.2d 403 (2010). And under the severability principle, we treat a challenge to the validity of an arbitration agreement (or a delegation clause) separately from a challenge to the validity of the entire contract in which it appears. Id., at 70-71, 130 S.Ct. 2772. Unless a party specifically challenges the validity of the agreement to arbitrate, both sides may be required to take all their disputes-including disputes about the validity of their broader contract-to arbitration. Ibid. Applying these principles to this case, New Prime notes that Mr. Oliveira has not specifically challenged the parties delegation clause and submits that any controversy should therefore proceed only and immediately before an arbitrator.
But all this overlooks the necessarily antecedent statutory inquiry weve just discussed. A delegation clause is merely a specialized type of arbitration agreement, and the Act operates on this additional arbitration agreement just as it does on any other. Id., at 70, 130 S.Ct. 2772. So a court may use §§ 3 and 4 to enforce a delegation clause only if the clause appears in a written provision in ... a contract evidencing a transaction involving commerce consistent with § 2. And only if the contract in which the clause appears doesnt trigger § 1s contracts of employment exception. In exactly the same way, the Acts severability principle applies only if the parties arbitration agreement appears in a contract that falls within the field §§ 1 and 2 describe. We acknowledged as much some time ago, explaining that, before invoking the severability principle, a court should determine[ ] that the contract in question is within the coverage of the Arbitration Act. Prima Paint Corp. v. Flood & Conklin Mfg. Co., 388 U.S. 395, 402, 87 S.Ct. 1801, 18 L.Ed.2d 1270 (1967).
III
That takes us to the second question: Did the First Circuit correctly resolve the merits of the § 1 challenge in this case? Recall that § 1 excludes from the Acts compass contracts of employment of ... workers engaged in ... interstate commerce. Happily, everyone before us agrees that Mr. Oliveira qualifies as a worker[ ] engaged in ... interstate commerce. For purposes of this appeal, too, Mr. Oliveira is willing to assume (but not grant) that his contracts with New Prime establish only an independent contractor relationship.
With that, the disputed question comes into clear view: What does the term contracts of employment mean? If it refers only to contracts that reflect an employer-employee relationship, then § 1s exception is irrelevant and a court is free to order arbitration, just as New Prime urges. But if the term also encompasses contracts that require an independent contractor to perform work, then the exception takes hold and a court lacks authority under the Act to order arbitration, exactly as Mr. Oliveira argues.
A
In taking up this question, we bear an important caution in mind. [I]ts a fundamental canon of statutory construction that words generally should be interpreted as taking their ordinary ... meaning ... at the time Congress enacted the statute. Wisconsin Central Ltd. v. United States, 585 U.S. ----, ----, 138 S.Ct. 2067, 2074, 201 L.Ed.2d 490 (2018) (quoting Perrin v. United States, 444 U.S. 37, 42, 100 S.Ct. 311, 62 L.Ed.2d 199 (1979) ). See also Sandifer v. United States Steel Corp., 571 U.S. 220, 227, 134 S.Ct. 870, 187 L.Ed.2d 729 (2014). After all, if judges could freely invest old statutory terms with new meanings, we would risk amending legislation outside the single, finely wrought and exhaustively considered, procedure the Constitution commands. INS v. Chadha, 462 U.S. 919, 951, 103 S.Ct. 2764, 77 L.Ed.2d 317 (1983). We would risk, too, upsetting reliance interests in the settled meaning of a statute. Cf. 2B N. Singer & J. Singer, Sutherland on Statutes and Statutory Construction § 56A:3 (rev. 7th ed. 2012). Of course, statutes may sometimes refer to an external source of law and fairly warn readers that they must abide that external source of law, later amendments and modifications included. Id ., § 51:8 (discussing the reference canon). But nothing like that exists here. Nor has anyone suggested any other appropriate reason that might allow us to depart from the original meaning of the statute at hand.
That, we think, holds the key to the case. To many lawyerly ears today, the term contracts of employment might call to mind only agreements between employers and employees (or what the common law sometimes called masters and servants). Suggestively, at least one recently published law dictionary defines the word employment to mean the relationship between master and servant. Blacks Law Dictionary 641 (10th ed. 2014). But this modern intuition isnt easily squared with evidence of the terms meaning at the time of the Acts adoption in 1925. At that time, a contract of employment usually meant nothing more than an agreement to perform work. As a result, most people then would have understood § 1 to exclude not only agreements between employers and employees but also agreements that require independent contractors to perform work.
Whats the evidence to support this conclusion? It turns out that in 1925 the term contract of employment wasnt defined in any of the (many) popular or legal dictionaries the parties cite to us. And surely thats a first hint the phrase wasnt then a term of art bearing some specialized meaning. It turns out, too, that the dictionaries of the era consistently afforded the word employment a broad construction, broader than may be often found in dictionaries today. Back then, dictionaries tended to treat employment more or less as a synonym for work. Nor did they distinguish between different kinds of work or workers: All work was treated as employment, whether or not the common law criteria for a master-servant relationship happened to be satisfied.
What the dictionaries suggest, legal authorities confirm. This Courts early 20th-century cases used the phrase contract of employment to describe work agreements involving independent contractors. Many state court cases did the same. So did a variety of federal statutes. And state statutes too. We see here no evidence that a contract of employment necessarily signaled a formal employer-employee or master-servant relationship.
More confirmation yet comes from a neighboring term in the statutory text.
Recall that the Act excludes from its coverage contracts of employment of ... any ... class of workers engaged in foreign or interstate commerce. 9 U.S.C. § 1 (emphasis added). Notice Congress didnt use the word employees or servants, the natural choices if the term contracts of employment addressed them alone. Instead, Congress spoke of workers, a term that everyone agrees easily embraces independent contractors. That word choice may not mean everything, but it does supply further evidence still that Congress used the term contracts of employment in a broad sense to capture any contract for the performance of work by workers .
B
What does New Prime have to say about the case building against it? Mainly, it seeks to shift the debate from the term contracts of employment to the word employee. Today, the company emphasizes, the law often distinguishes between employees and independent contractors. Employees are generally understood as those who work in the service of another person (the employer) under an express or implied contract of hire, under which the employer has the right to control the details of work performance. Blacks Law Dictionary, at 639. Meanwhile, independent contractors are sometimes described as those entrusted to undertake a specific project but who [are] left free to do the assigned work and to choose the method for accomplishing it. Id., at 888. New Prime argues that, by 1925, the words employee and independent contractor had already assumed these distinct meanings. And given that, the company contends, the phrase contracts of employment should be understood to refer only to relationships between employers and employees .
Unsurprisingly, Mr. Oliveira disagrees. He replies that, while the term employment dates back many centuries, the word employee only made its first appearance in English in the 1800s. See Oxford English Dictionary (3d ed., Mar. 2014), www.oed.com/view/Entry/61374 (all Internet materials as last visited Jan. 9, 2019). At that time, the word from which it derived, employ, simply meant to apply (a thing) to some definite purpose. 3 J. Murray, A New English Dictionary on Historical Principles 129 (1891). And even in 1910, Blacks Law Dictionary reported that the term employee had only become somewhat naturalized in our language. Blacks Law Dictionary 421 (2d ed. 1910).
Still, the parties do share some common ground. They agree that the word employee eventually came into wide circulation and came to denote those who work for a wage at the direction of another. They agree, too, that all this came to pass in part because the word employee didnt suffer from the same historical baggage of the older common law term servant, and because it proved useful when drafting legislation to regulate burgeoning industries and their labor forces in the early 20th century. The parties even agree that the development of the term employee may have come to influence and narrow our understanding of the word employment in comparatively recent years and may be why today it might signify to some a relationship between master and servant.
But if the parties extended etymological debate persuades us of anything, it is that care is called for. The words employee and employment may share a common root and an intertwined history. But they also developed at different times and in at least some different ways. The only question in this case concerns the meaning of the term contracts of employment in 1925. And, whatever the word employee may have meant at that time, and however it may have later influenced the meaning of employment, the evidence before us remains that, as dominantly understood in 1925, a contract of employment did not necessarily imply the existence of an employer-employee or master-servant relationship.
When New Prime finally turns its attention to the term in dispute, it directs us to Coppage v. Kansas, 236 U.S. 1, 13, 35 S.Ct. 240, 59 L.Ed. 441 (1915). There and in other cases like it, New Prime notes, courts sometimes used the phrase contracts of employment to describe what today wed recognize as agreements between employers and employees. But this proves little. No one doubts that employer-employee agreements to perform work qualified as contracts of employment in 1925-and documenting that fact does nothing to negate the possibility that contracts of employment also embraced agreements by independent contractors to perform work. Coming a bit closer to the mark, New Prime eventually cites a handful of early 20th-century legal materials that seem to use the term contracts of employment to refer exclusively to employer-employee agreements. But from the record amassed before us, these authorities appear to represent at most the vanguard, not the main body, of contemporaneous usage.
New Primes effort to explain away the statutes suggestive use of the term worker proves no more compelling. The company reminds us that the statute excludes contracts of employment for seamen and railroad employees as well as other transportation workers. And because seamen and railroad employees included only employees in 1925, the company reasons, we should understand any other class of workers engaged in ... interstate commerce to bear a similar construction. But this argument rests on a precarious premise. At the time of the Acts passage, shipboard surgeons who tended injured sailors were considered seamen though they likely served in an independent contractor capacity. Even the term railroad employees may have swept more broadly at the time of the Acts passage than might seem obvious today. In 1922, for example, the Railroad Labor Board interpreted the word employee in the Transportation Act of 1920 to refer to anyone engaged in the customary work directly contributory to the operation of the railroads. And the Erdman Act, a statute enacted to address disruptive railroad strikes at the end of the 19th century, seems to evince an equally broad understanding of railroad employees.
Unable to squeeze more from the statutes text, New Prime is left to appeal to its policy. This Court has said that Congress adopted the Arbitration Act in an effort to counteract judicial hostility to arbitration and establish a liberal federal policy favoring arbitration agreements. Moses H. Cone Memorial Hospital v. Mercury Constr. Corp., 460 U.S. 1, 24, 103 S.Ct. 927, 74 L.Ed.2d 765 (1983). To abide that policy, New Prime suggests, we must order arbitration according to the terms of the parties agreement. But often and by design it is hard-fought compromise[ ], not cold logic, that supplies the solvent needed for a bill to survive the legislative process. Board of Governors, FRS v. Dimension Financial Corp., 474 U.S. 361, 374, 106 S.Ct. 681, 88 L.Ed.2d 691 (1986). If courts felt free to pave over bumpy statutory texts in the name of more expeditiously advancing a policy goal, we would risk failing to tak[e] ... account of legislative compromises essential to a laws passage and, in that way, thwart rather than honor the effectuation of congressional intent. Ibid. By respecting the qualifications of § 1 today, we respect the limits up to which Congress was prepared to go when adopting the Arbitration Act. United States v. Sisson, 399 U.S. 267, 298, 90 S.Ct. 2117, 26 L.Ed.2d 608 (1970).
Finally, and stretching in a different direction entirely, New Prime invites us to look beyond the Act. Even if the statute doesnt supply judges with the power to compel arbitration in this case, the company says we should order it anyway because courts always enjoy the inherent authority to stay litigation in favor of an alternative dispute resolution mechanism of the parties choosing. That, though, is an argument we decline to tangle with. The courts below did not address it and we granted certiorari only to resolve existing confusion about the application of the Arbitration Act, not to explore other potential avenues for reaching a destination it does not.
*
When Congress enacted the Arbitration Act in 1925, the term contracts of employment referred to agreements to perform work. No less than those who came before him, Mr. Oliveira is entitled to the benefit of that same understanding today. Accordingly, his agreement with New Prime falls within § 1s exception, the court of appeals was correct that it lacked authority under the Act to order arbitration, and the judgment is
Affirmed.
Justice KAVANAUGH took no part in the consideration or decision of this case.
See, e.g., 3 J. Murray, A New English Dictionary on Historical Principles 130 (1891) (defining employment as, among other things, [t]he action or process of employing; the state of being employed. The service (of a person). That on which (one) is employed; business; occupation; a special errand or commission. A persons regular occupation or business; a trade or profession); 3 The Century Dictionary and Cyclopedia 1904 (1914) (defining employment as [w]ork or business of any kind); W. Harris, Websters New International Dictionary 718 (1st ed. 1909) (listing work as a synonym for employment); Websters Collegiate Dictionary 329 (3d ed. 1916) (same); Blacks Law Dictionary 422 (2d ed. 1910) (an engagement or rendering services for oneself or another); 3 Oxford English Dictionary 130 (1933) ([t]hat on which (one) is employed; business; occupation; a special errand or commission).
See, e.g ., Watkins v. Sedberry, 261 U.S. 571, 575, 43 S.Ct. 411, 67 L.Ed. 802 (1923) (agreement between trustee and attorney to recover bankrupts property); Owen v. Dudley & Michener, 217 U.S. 488, 494, 30 S.Ct. 602, 54 L.Ed. 851 (1910) (agreement between Indian tribe and attorneys to pursue claims).
See, e.g ., Lindsay v. McCaslin (Two Cases), 123 Me. 197, 200, 122 A. 412, 413 (1923) (When the contract of employment has been reduced to writing, the question whether the person employed was an independent contractor or merely a servant is determined by the court as a matter of law); Tankersley v. Webster, 116 Okla. 208, 210, 243 P. 745, 747 (1925) ([T]he contract of employment between Tankersley and Casey was admitted in evidence without objections, and we think conclusively shows that Casey was an independent contractor); Waldron v. Garland Pocahontas Coal Co., 89 W.Va. 426, 427, 109 S.E. 729 (1921) (syllabus) ( Whether a person performing work for another is an independent contractor depends upon a consideration of the contract of employment, the nature of the business, the circumstances under which the contract was made and the work was done); see also App. to Brief for Respondent 1a-12a (citing additional examples).
See, e.g., Act of Mar. 19, 1924, ch. 70, § 5, 43 Stat. 28 (limiting payment of fees to attorneys employed by the Cherokee Tribe to litigate claims against the United States to those stipulated in the contract of employment); Act of June 7, 1924, ch. 300, §§ 2, 5, 43 Stat. 537 -538 (providing same for Choctaw and Chickasaw Tribes); Act of Aug. 24, 1921, ch. 89, 42 Stat. 192 (providing that no funds may be used to compensate any attorney, regular or special, for the United States Shipping Board or the United States Shipping Board Emergency Fleet Corporation unless the contract of employment has been approved by the Attorney General of the United States). See also App. to Brief for Respondent 13a (citing additional examples).
See, e.g., Act of Mar. 10, 1909, ch. 70, § 1, 1909 Kan. Sess. Laws p. 121 (referring to contracts of employment of auditors, accountants, engineers, attorneys, counselors and architects for any special purpose); Act of Mar. 4, 1909, ch. 4, § 4, 1909 Okla. Sess. Laws p. 118 (Should the amount of the attorneys fee be agreed upon in the contract of employment, then such attorneys lien and cause of action against such adverse party shall be for the amount so agreed upon); Act of Mar. 4, 1924, ch. 88, § 1, 1924 Va. Acts ch. 91 (allowing extension of contracts of employment between the state and contractors with respect to the labor of prisoners); App. to Brief for Respondent 14a-15a (citing additional examples).
See, e.g., Atlantic Transp. Co. v. Coneys, 82 F. 177, 178 (C.A.2 1897) ; Nyback v. Champagne Lumber Co., 109 F. 732, 741 (C.A.7 1901).
See Carlson, Why the Law Still Cant Tell an Employee When It Sees One and How It Ought To Stop Trying, 22 Berkeley J. Emp. & Lab. L. 295, 309 (2001) (discussing the historical baggage of the term servant); Broden, General Rules Determining the Employment Relationship Under Social Security Laws: After Twenty Years an Unsolved Problem, 33 Temp. L.Q. 307, 327 (1960) (describing use of the term employer-employee, in contradistinction to master-servant, in the Social Security laws). Legislators searched to find a term that fully encompassed the broad protections they sought to provide and considered an assortment of vague and uncertain terms, including servant, ... employee, ... workman, laborer, wage earner, operative, or hireling. Carlson, 22 Berkeley J. Emp. & Lab. L., at 308. Eventually employee prevailed, if only by default, and the choice was confirmed by the next wave of protective legislation-workers compensation laws in the early years of the Twentieth Century. Id., at 309.
Blacks Law Dictionary 641 (10th ed. 2014); see also P. Durkin, Release Notes: The Changes in Empathy, Employ, and Empire (Mar. 13, 2014) (Over time the meaning of several employ-related words have reflect[ed] changes in the world of work and their meaning shows an increasingly marked narrowing), online at https://public.oed.com/blog/march-2014-update-release-notes/.
See, e.g., 1 T. Conyngton, Business Law: A Working Manual of Every-day Law 302-303 (2d ed. 1920); Newland v. Bear, 218 App.Div. 308, 309, 218 N.Y.S. 81, 81-82 (1926) ; Anderson v. State Indus. Accident Commn, 107 Ore. 304, 311-312, 215 P. 582, 583, 585 (1923) ; N. Dosker, Manual of Compensation Law: State and Federal 8 (1917).
See, e.g., The Sea Lark, 14 F.2d 201 (W.D.Wash.1926) ; The Buena Ventura, 243 F. 797, 799 (S.D.N.Y.1916) ; Holt v. Cummings, 102 Pa. 212, 215 (1883) ; Allan v. State S.S. Co., 132 N.Y. 91, 99, 30 N.E. 482, 485 (1892) (The work which the physician does after the vessel starts on the voyage is his and not the ship owners).
Transportation Act of 1920, §§ 304, 307, 41 Stat. 456 ; Railway Employees Dept., A.F. of L. v. Indiana Harbor Belt R. Co ., Decision No. 982, 3 R.L.B. 332, 337 (1922).
The Act provided for arbitration between railroads and workers, and defined employees as all persons actually engaged in any capacity in train operation or train service of any description. Act of June 1, 1898, ch. 370, 30 Stat. 424. The Act also specified that the railroads would be responsible for the acts and defaults of such employees in the same manner and to the same extent as if ... said employees [were] directly employed by it. Id., at 425. See Dempsey, Transportation: A Legal History, 30 Transp. L.J. 235, 273 (2003).