More than 50 years ago, Mr. Justice Brandeis observed in dissent in International News Service v. Associated Press:
The general rule of law is, that the noblest of human productions -- knowledge, truths ascertained, conceptions, and ideas -- become, after voluntary communication to others, free as the air to common use.
248 U.S. 215, 250 (1918).
 But there is no fixed, immutable line to tell us which "human productions" are private property and which are so general as to become "free as the air." In earlier times, a performing artist's work was largely restricted to the stage; once performed, it remained "recorded" only in the memory of those who had seen or heard it. Today, we can record that performance in precise detail [p*571] and reproduce it again and again with utmost fidelity. The California statutory scheme evidences a legislative policy to prohibit "tape piracy" and "record piracy," conduct that may adversely affect the continued production of new recordings, a large industry in California. Accordingly, the State has, by statute, given to recordings the attributes of property. No restraint has been placed on the use of an idea or concept; rather, petitioners and other individuals remain free to record the same compositions in precisely the same manner and with the same personnel as appeared on the original recording.
 In sum, we have shown that § 653h does not conflict with the federal copyright statute enacted by Congress in 109. Similarly, no conflict exists between the federal copyright statute passed in 1971 and the present application of § 653h, since California charged petitioners only with copying recordings fixed prior to February 15, 1972.[n29] Finally, we have concluded that our decisions in Sears and Compco, which we reaffirm today, have no application in the present case, since Congress has indicated neither that it wishes to protect, nor to free from protection, recordings of musical performances fixed prior to February 15, 1972
 We conclude that the State of California has exercised a power which it retained under the Constitution, and that the challenged statute, as applied in this case, does not intrude into an area which Congress has, up to now, preempted. Until and unless Congress takes further action with respect to recordings fixed prior to February 15, 1972, the California statute may be enforced against acts of piracy such as those which occurred in the present case.
 Affirmed. [p*572]
1. In pertinent part, the California statute provides:
(a) Every person is guilty of a misdemeanor who: (1) Knowingly and willfully transfers or causes to be transferred any sounds recorded on a phonograph record, . . . tape, . . . or other article on which sounds are recorded, with intent to sell or cause to be sold, . . . such article on which such sounds are so transferred, without the consent of the owner. (2) . . . * * * * (b) As used in this section, "person" means any individual, partnership, corporation or association; and "owner" means the person who owns the master phonograph record, . . . master tape, . . . or other device used for reproducing recorded sounds on phonograph records, . . . tapes, . . . or other articles on which sound is recorded, and from which the transferred recorded sounds are directly or indirectly derived. Specifically, each count of the information alleged that, in regard to a particular recording, petitioners had, at and in the City of Los Angeles, in the County of Los Angeles, State of California . . . willfully, unlawfully and knowingly transferred and caused to be transferred sounds recorded on a tape with the intent to sell and cause to be sold, such tape on which such sounds [were] so transferred. . . .
2. Article I, § 8, cl. 8, provides that Congress shall have the power To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries. . . .
3. Since petitioners did not proceed to trial, the factual record before the Court is sparse. However, both parties indicate that a complete description of petitioners' method of operation may be found in the record of Tape Industries Assn. of America v. Younger, 316 F.Supp. 340 (CD Cal.1970), appeal dismissed for lack of jurisdiction, 401 U.S. 902 (1971), appeal pending United States Court of Appeals, CA9, No. 26,628.
4. An additional label was attached to each cartridge by petitioners, stating that no relationship existed between petitioners and the producer of the original recording or the individuals whose performances had been recorded. Consequently, no claim is made that petitioners misrepresented the source of the original recordings or the manufacturer of the tapes.
5. The costs of producing a single original long-playing record of a musical performance may exceed $50,000 or $100,000. Tape Industries Assn. of America v. Younger, supra, at 344; Hearings on S. 646 and H.R. 6927 before Subcommittee No. 3 of the House Committee on the Judiciary, 92d Cong., 1st Sess., 27-28 (1971). For the performance recorded on this record, petitioners would pay only the retail cost of a single long-playing record or a single tape.
6. Title 17 U.S.C. § 2 provides: Nothing in this title shall be construed to annul or limit the right of the author or proprietor of an unpublished work, at common law or in equity, to prevent the copying, publication, or use of such unpublished work without his consent, and to obtain damages therefor.
7. No question is raised in the present case as to the power of the States to protect recordings fixed after February 15, 1972.
8. The Federalist No. 32, p. 241 (B. Wright ed.1961); see Cooley v. Board of Wardens, 12 How. 299, 318-319 (1851).
9. Art. I, § 8, cl. 3.
10. See Kendall v. Winsor, 21 How. 322, 328 (1859); Mitchell v. Tilghman, 19 Wall. 287, 418 (1874); Bauer v. O'Donnell, 229 U.S. l, 10 (1913).
11. The Federalist No. 43, p. 309 (B. Wright ed.1961). ___,
12. Numerous examples may be found in our early history of the difficulties which the creators of items of national import had in securing protection of their creations in all States. For example, Noah Webster, in his effort to obtain protection for his book, A Grammatical Institute of the English Language, brought his claim before the legislatures of at least six States, and perhaps as many as 12. See B. Bugbee, The Genesis of American Patent and Copyright Law 108-110, 120-124 (Wash., D.C.1967); H.R.Rep. No. 2222, 60th Cong., 2d Sess., 2 (1909). Similar difficulties were experienced by John Fitch and other inventors who desired to protect their efforts to perfect a steamboat. See Federico, State Patents, 13 J. Pat.Off.Soc. 166, 170-176 (1931).
13. As early as 1751, Massachusetts granted to Benjamin Crabb the exclusive right to employ a specific process for the manufacture of candles out of whale oil. It is not clear whether Crabb invented the process. The Acts and Resolves, Public and Private, of the Province of the Massachusetts Bay, Vol. 3, Session of Jan. 10, 1751, c.19, pp. 546-547 ( 1878). In 1780, Pennsylvania granted a patent to Henry Guest for the processing of tanning oil and blubber, noting specifically that the patent was "a reward for his discovery and for the purpose of promoting useful manufactories in this state." The Statutes at Large of Pennsylvania from 1682 to 1801, Vol. 10, p. 132 (J. Mitchell & H. Flanders eds.1904). Similarly, South Carolina granted protection to Peter Belin in 1786 for newly designed waterworks which aided in the production of rice, a staple of South Carolina agriculture, and other products. Another patent relating to the processing of rice was granted by South Carolina in 1788. The Statutes at Large of South Carolina, Vol. 4, p. 755 (T. Cooper ed. 1838); id. Vol. 5, p. 69 (1839). In 1787, Maryland granted a patent on a spinning and carding machine "to encourage useful inventions, as well as promote the manufacture of cotton and wool within this state. . . ." The Laws of Maryland, Vol. 2, Session of Nov. 6, 1786-Jan. 20, 1787, c. 23 (W. Kilty ed. 1800). In the same year, Pennsylvania patented certain devices relating to flour mills, noting that these devices would "tend to simplify and render cheap the manufacture of flour which is one of the principal staples of this commonwealth. . . ." The Statutes at Large of Pennsylvania from 1682 to 1801, Vol. 12, pp. 483-484 (J. Mitchell & H. Flanders eds.1906).
14. The Federalist No. 42, p. 305 (B. Wright ed.1961).
15. Cf. Morgan v. Virginia, 328 U.S. 373 (1946); Bibb v. Navajo Freight Lines, 359 U.S. 520 (1959); Southern Pacific Co. v. Arizona, 325 U.S. 761 (1945); Pennsylvania v. West Virginia, 262 U.S. 553 (1923).
16. For example, Congress has allowed writings which may eventually be the subject of a federal copyright, to be protected under state law prior to publication. 17 U.S.C. § 2.
17. The first congressional copyright statute, passed in 1790, governed only maps, charts, and books. Act of May 31, 1790, c. 15, 1 Stat. 124. In 1802, the Act was amended in order to grant protection to any person "who shall invent and design, engrave, etch or work . . . any historical or other print or prints. . . ." Act of Apr. 29, 1802, c. 36, 2 Stat. 171. Protection was extended to musical compositions when the copyright laws were revised in 1831. Act of Feb. 3, 1831, c. 16, 4 Stat. 436. In 1865, at the time when Mathew Brady's pictures of the Civil War were attaining fame, photographs and photographic negatives were expressly added to the list of protected works. Act of Mar. 3, 1865, c. 126, 13 Stat. 540. Again in 1870, the list was augmented to cover paintings, drawings, chromos, statuettes, statuary, and models or designs of fine art. Act of July 8, 1870, c. 230, 16 Stat. 198. In 1909, Congress agreed to a major consolidation and amendment of all federal copyright statutes. A list of 11 categories of protected works was provided. The relevant sections of the Act are discussed in the text of our opinion. The House Report on the proposed bill specifically noted that amendment was required because "the reproduction of various things which are the subject of copyright has enormously increased," and that the President has specifically recommended revision, among other reasons, because the prior laws "omit[ted] provision for many articles which, under modern reproductive processes, are entitled to protection." H.R.Rep. No. 2222, supra, n. 12, at 1 (quoting Samuel J. Elder and President Theodore Roosevelt). Since 1909, two additional amendments have been added. In 1912, the list of categories in § 5 was expanded specifically to include motion pictures. The House Report on the amendment noted: The occasion for this proposed amendment is the fact that the production of motion picture photoplays and motion pictures other than photoplays has become a business of vast proportions. The money invested therein is so great and the property rights so valuable that the committee is of the opinion that the copyright law ought to be so amended as to give to them distinct and definite recognition and protection. H.R.Rep. No. 756, 62d Cong., 2d Sess., 1 (1912). Finally, in 1971, § 5 was amended to include "sound recordings." Congress was spurred to action by the growth of record piracy, which was, in turn, due partly to technological advances. See Hearings on S. 646 and H.R. 6927, supra, n. 5, at 4-5, 11 (1971). It must be remembered that the "record piracy" charged against petitioners related to recordings fixed by the original producer prior to Feb. 15, 1972, the effective date of the 1971 Act. See supra at 551-552.
18. 17 U.S.C. § 1(e)
19. H.R.Rep. No. 7083, 59th Cong., 2d Sess., pt.. 2, p. 2 (1907) (Minority Report).
20. After all, what is the perforated roll? The fact is clearly established in the testimony in this case that even those skilled in the making of these rolls are unable to read them as musical compositions, as those in staff notation are read by the performer. . . . These perforated rolls are parts of a machine which, when duly applied and properly operated in connection with the mechanism to which they are adapted, produce musical tones in harmonious combination. But we cannot think that they are copies within the meaning of the copyright act. White-Smith Music Publishing Co. v. Apollo Co., 209 U.S. 1, 18 (1908).
21. H.R.Rep. No. 7083, supra, n.19, pt.. 1, at 10; pt.. 2, at 3.
22. This is especially clear from the comment made by the Committee on Patents in regard to a foreign statute which, to some extent, protected performances. The committee stated that the foreign statute in no way affects the reproduction of such music by phonographs, graphophones, or the ordinary piano-playing instruments, for, in these instruments, the reproduction is purely mechanical. H.R.Rep. No. 2222, supra, n. 12, at 5.
23. Petitioners do not argue that § 653h conflicts with that portion of 17 U.S.C. § 1(e) which provides: [W]henever the owner of a musical copyright has used or permitted or knowingly acquiesced in the use of the copyrighted work upon the parts of instruments serving to reproduce mechanically the musical work, any other person may make similar use of the copyrighted work upon the payment to the copyright proprietor of a royalty of 2 cents on each such part manufactured. . . . Assuming, arguendo, that petitioners' use of the composition they duplicated constitutes a "similar use," the challenged state statute might be claimed to diminish the return which is due the composer by lessening the number of copies produced, and thus to conflict with § 1(e). However, as we have noted above, the means presently available for reproducing recordings were not in existence in 1909, when 17 U.S.C. § 1(e) was passed. We see no indication that the challenged state statute detracts from royalties which Congress intended the composer to receive. Furthermore, many state statutes may diminish the number of copies produced. Taxing statutes, for example, may raise the cost of producing or selling records and thereby lessen the number of records which may be sold or inhibit new companies from entering this field of commerce. We do not see in these statutes the direct conflict necessary to render a state statute invalid.
24. H.R.Rep. No. 2222, supra, n. 12, at 10.
25. The registration of records under the provisions of the 1909 Act would give rise to numerous administrative difficulties. It is difficult to discern how an individual who wished to copyright a record could comply with the notice and deposit provisions of the statute. 17 U.S.C. §§ 12, 13, 19, 20. Nor is it clear to whom the copyright could rightfully be issued or what constituted publication. Finally, the administrative and economic burden of classifying and maintaining copies of records would have been considerable. See Chafee, Reflections on the Law of Copyright; II, 45 Col.L.Rev. 719, 735 (1945); Ringer, The Unauthorized Duplication of Sound Recordings, Studies Prepared for the Subcommittee on Patents, Trademarks, and Copyrights of the Senate Committee on the Judiciary, 86th Cong., 2d Sess., 2 (comm. print 1961); Hearings on S. 646 and H.R. 6927, supra, n. 5, at 11, 14.
26. Fonotipia, Ltd. v. Bradley, 171 F. 951, 963 (EDNY 1909).
27. Aeolian Co. v. Royal Music Roll Co., 196 F. 926, 927 (WDNY 1912); Waring v. WDAS Broadcasting Station, 327 Pa. 433, 437-438, 194 A. 631, 633-634 (1937); Capitol Records, Inc. v. Mercury Records Corp., 221 F.2d 657, 661-662 (CA2 1955); Jerome v. Twentieth Century Fox-Film Corp., 67 F.Supp. 736, 742 (SDNY 1946).
28. Petitioners place great stress on their belief that the records or tapes which they copied had been "published." We have no need to determine whether, under state law, these recordings had been published or what legal consequences such publication might have. For purposes of federal law, "publication" serves only as a term of the art which defines the legal relationships which Congress has adopted under the federal copyright statutes. As to categories of writings which Congress has not brought within the scope of the federal statute, the term has no application.
29. Supra at 551-552.
MR. JUSTICE DOUGLAS, with whom MR. JUSTICE BRENNAN and MR. JUSTICE BLACKMUN concur, dissenting.
 Article I, § 8, cl. 8, of the Constitution provides:
The Congress shall have Power . . . [t]o promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries.
 Madison made a brief comment on this provision governing both patents and copyrights:
The States cannot separately make effectual provision for either of the cases, and most of them have anticipated the decision of this point, by laws passed at the instance of Congress.[n1]
 Prior to February 25, 1972, copyright protection was not extended to sound recordings. Sears and Compco make clear that the federal policy expressed in Art. I, § 8, cl. 8, is to have "national uniformity in patent and copyright laws," 376 U.S. at 231 n. 7, a policy bolstered by Acts of Congress which vest
exclusive jurisdiction to hear patent and copyright cases in federal courts . . . and that section of the Copyright Act which expressly saves state protection of unpublished writings, but does not include published writings.
 Prior to February 15, 1972,[n2] sound recordings had no [p*574] copyright protection. And, even under that Act, the copyright would be effective
only to sound recordings fixed, published, and copyrighted on and after the effective date of this Act [Feb. 15, 1972] and before January 1, 1975.[n3]
 California's law promotes monopoly; the federal policy promotes monopoly only when a copyright is issued, and it fosters competition in all other instances. Moreover, federal law limits its monopoly to 28 years plus a like renewal period,[n4] while California extends her monopoly into perpetuity.
 The need for uniformity was stated by Judge Learned Hand in a dissent in Capitol Records, Inc. v. Mercury Records Corp., 221 F.2d 657. That case involved the duplication of uncopyrighted sound recordings, the court holding that state law prevailed where there was no federal copyright provision. Judge Hand emphasized in his dissent that "uniformity" was one of the principal purposes of the Patent and Copyright Clause, and that uniformity could be obtained only by preemption. He said:
If, for example, in the case at bar, the defendant is forbidden to make and sell these records in New York, that will not prevent it from making and selling them in any other state which may regard the plaintiff's sales as a "publication;" and it will be practically impossible to prevent their importation into New York. That is exactly the kind of evil at which the clause is directed.
Id. at 667.
 I would reverse the judgment below. [p*576]
1. The Federalist No. 43, p. 309 (B. Wright ed.1961).
2. The effective date of Pub.L. 92-140, 85 Stat. 392.
3. Id., § 3.
4. 17 U.S.C. § 24.
MR. JUSTICE MARSHALL, with whom MR. JUSTICE BRENNAN and MR. JUSTICE BLACKMUN join, dissenting.
 The argument of the Court, as I understand it, is this:
Since sound recordings fixed prior to February 15, 1972, were not enumerated by Congress as subject to copyrighting,[n1] the States may protect such recordings. [p*577]
 With respect, I cannot accept the final step of this argument. In my view, Congress has demonstrated its desire to exercise the full grant of constitutional power. Title 17 U.S.C. § 4, states: "The works for which copyright may be secured under this title shall include all the writings of an author" (emphasis added). The use of the constitutional terms "writings" and "author" rather strongly suggests that Congress intended to follow the constitutional grant. Nor can I find in the course of legislation sufficient evidence to convince me that Congress determined to permit state regulation of the reproduction of sound recordings. For whenever technological advances made extension of copyright protection seem wise, Congress has acted promptly. See ante at 562-563, n. 17.[n4] This seems to me to reflect the same judgment that the Court found in [p*579] Sears and Compco: Congress has decided that free competition should be the general rule until it is convinced that the failure to provide copyright or patent protection is hindering "the Progress of Science and useful Arts."
 I would therefore hold that, as to sound recordings fixed before February 15, 1972, the States may not enforce laws limiting reproduction.
1. Sound recordings fixed after that date may be copyrighted. Pub.L. 92-140, 85 Stat. 391, 17 U.S.C. § 5(n) (1970 ed., Supp. I).
4. Between 1909 and 1951, Congress' attention was repeatedly drawn to problems of copyrighting sound recordings. Many bills to provide copyright protection for such recordings were introduced, but none was enacted. See Ringer, The Unauthorized Duplication of Sound Recordings, Studies Prepared for the Subcommittee on Patents, Trademarks, and Copyrights of the Senate Committee on the Judiciary, 86th Cong., 2d Sess., 21-37 (Comm.Print 1961). Respondent argues that Congress failed to enact these bills primarily out of uncertainty about the relationship between federal law and international copyright conventions, and was comforted in the knowledge that protection was available under state law. See Brief for Respondent 28-32. However, it is enough that Congress was aware of the problem, and could have acted, as it did when other technological innovations presented new problems, rather expeditiously. The problems that Congress confronted in 1971 did not spring up in 1970, but had existed, and Congress had not acted, for many years before.
ProCD, INC. v. ZEIDENBERG, 86 F.3d 1447 (7th. Cir. 1996)
Before COFFEY, FLAUM, and EASTERBROOK, Circuit Judges.
EASTERBROOK, Circuit Judge.
 Must buyers of computer software obey the terms of shrinkwrap licenses? The district court held not, for two reasons: first, they are not contracts because the licenses are inside the box rather than printed on the outside; second, federal law forbids enforcement even if the licenses are contracts. 908 F. Supp. 640 (W.D. Wis. 1996). The parties and numerous amici curiae have briefed many other issues, but these are the only two that matter - and we disagree with the district judge's conclusion on each. Shrinkwrap licenses are enforceable unless their terms are objectionable on grounds applicable to contracts in general (for example, if they violate a rule of positive law, or if they are unconscionable). Because no one argues that the terms of the license at issue here are troublesome, we remand with instructions to enter judgment for the plaintiff.
 ProCD, the plaintiff, has compiled information from more than 3,000 telephone directories into a computer database. We may assume that this database cannot be copyrighted, although it is more complex, contains more information (nine-digit zip codes and census industrial codes), is organized differently, and therefore is more original than the single alphabetical directory at issue in Feist Publications, Inc. v. Rural Telephone Service Co., 499 U.S. 340 (1991). See Paul J. Heald, The Vices of Originality, 1991 Sup. Ct. Rev. 143, 160-68. ProCD sells a version of the database, called SelectPhone (trademark), on CD-ROM discs. (CD-ROM means "compact disc - read only memory." The "shrinkwrap license" gets its name from the fact that retail software packages are covered in plastic or cellophane "shrinkwrap," and some vendors, though not ProCD, have written licenses that become effective as soon as the customer tears the wrapping from the package. Vendors prefer "end user license," but we use the more common term.) A proprietary method of compressing the data serves as effective encryption too. Customers decrypt and use the data with the aid of an application program that ProCD has written. This program, which is copyrighted, searches the database in response to users' criteria (such as "find all people named Tatum in Tennessee, plus all firms with `Door Systems' in the corporate name"). The resulting lists (or, as ProCD prefers, "listings") can be read and manipulated by other software, such as word processing programs.
 The database in SelectPhone (trademark) cost more than $10 million to compile and is expensive to keep current. It is much more valuable to some users than to others. The combination of names, addresses, and sic codes enables manufacturers to compile lists of potential customers. Manufacturers and retailers pay high prices to specialized information intermediaries for such mailing lists; ProCD offers a potentially cheaper alternative. People with nothing to sell could use the database as a substitute for calling long distance information, or as a way to look up old friends who have moved to unknown towns, or just as a electronic substitute for the local phone book. ProCD decided to engage in price discrimination, selling its database to the general public for personal use at a low price (approximately $150 for the set of five discs) while selling information to the trade for a higher price. It has adopted some intermediate strategies too: access to the SelectPhone (trademark) database is available via the America On-line service for the price America Online charges to its clients (approximately $3 per hour), but this service has been tailored to be useful only to the general public.
 If ProCD had to recover all of its costs and make a profit by charging a single price - that is, if it could not charge more to commercial users than to the general public - it would have to raise the price substantially over $150. The ensuing reduction in sales would harm consumers who value the information at, say, $200. They get consumer surplus of $50 under the current arrangement but would cease to buy if the price rose substantially. If because of high elasticity of demand in the consumer segment of the market the only way to make a profit turned out to be a price attractive to commercial users alone, then all consumers would lose out - and so would the commercial clients, who would have to pay more for the listings because ProCD could not obtain any contribution toward costs from the consumer market.
 To make price discrimination work, however, the seller must be able to control arbitrage. An air carrier sells tickets for less to vacationers than to business travelers, using advance purchase and Saturday-night-stay requirements to distinguish the categories. A producer of movies segments the market by time, releasing first to theaters, then to pay-per-view services, next to the videotape and laserdisc market, and finally to cable and commercial tv. Vendors of computer software have a harder task. Anyone can walk into a retail store and buy a box. Customers do not wear tags saying "commercial user" or "consumer user." Anyway, even a commercial-user-detector at the door would not work, because a consumer could buy the software and resell to a commercial user. That arbitrage would break down the price discrimination and drive up the minimum price at which ProCD would sell to anyone.
 Instead of tinkering with the product and letting users sort themselves - for example, furnishing current data at a high price that would be attractive only to commercial customers, and two-year-old data at a low price - ProCD turned to the institution of contract. Every box containing its consumer product declares that the software comes with restrictions stated in an enclosed license. This license, which is encoded on the CD-ROM disks as well as printed in the manual, and which appears on a user's screen every time the software runs, limits use of the application program and listings to non-commercial purposes.
 Matthew Zeidenberg bought a consumer package of SelectPhone (trademark) in 1994 from a retail outlet in Madison, Wisconsin, but decided to ignore the license. He formed Silken Mountain Web Services, Inc., to resell the information in the SelectPhone (trademark) database. The corporation makes the database available on the Internet to anyone willing to pay its price - which, needless to say, is less than ProCD charges its commercial customers. Zeidenberg has purchased two additional SelectPhone (trademark) packages, each with an updated version of the database, and made the latest information available over the World Wide Web, for a price, through his corporation. ProCD filed this suit seeking an injunction against further dissemination that exceeds the rights specified in the licenses (identical in each of the three packages Zeidenberg purchased). The district court held the licenses ineffectual because their terms do not appear on the outside of the packages. The court added that the second and third licenses stand no different from the first, even though they are identical, because they might have been different, and a purchaser does not agree to - and cannot be bound by - terms that were secret at the time of purchase. 908 F. Supp. at 654.
 Following the district court, we treat the licenses as ordinary contracts accompanying the sale of products, and therefore as governed by the common law of contracts and the Uniform Commercial Code. Whether there are legal differences between "contracts" and "licenses" (which may matter under the copyright doctrine of first sale) is a subject for another day. See Microsoft Corp. v. Harmony Computers & Electronics, Inc., 846 F. Supp. 208 (E.D. N.Y. 1994). Zeidenberg does not argue that Silken Mountain Web Services is free of any restrictions that apply to Zeidenberg himself, because any effort to treat the two parties as distinct would put Silken Mountain behind the eight ball on ProCD's argument that copying the application program onto its hard disk violates the copyright laws. Zeidenberg does argue, and the district court held, that placing the package of software on the shelf is an "offer," which the customer "accepts" by paying the asking price and leaving the store with the goods. Peeters v. State, 154 Wis. 111, 142 N.W. 181 (1913). In Wisconsin, as elsewhere, a contract includes only the terms on which the parties have agreed. One cannot agree to hidden terms, the judge concluded. So far, so good - but one of the terms to which Zeidenberg agreed by purchasing the software is that the transaction was subject to a license. Zeidenberg's position therefore must be that the printed terms on the outside of a box are the parties' contract - except for printed terms that refer to or incorporate other terms. But why would Wisconsin fetter the parties' choice in this way? Vendors can put the entire terms of a contract on the outside of a box only by using microscopic type, removing other information that buyers might find more useful (such as what the software does, and on which computers it works), or both. The "Read Me" file included with most software, describing system requirements and potential incompatibilities, may be equivalent to ten pages of type; warranties and license restrictions take still more space. Notice on the outside, terms on the inside, and a right to return the software for a refund if the terms are unacceptable (a right that the license expressly extends), may be a means of doing business valuable to buyers and sellers alike. See E. Allan Farnsworth, 1 Farnsworth on Contracts sec. 4.26 (1990); Restatement (2d) of Contracts sec. 211 comment a (1981) ("Standardization of agreements serves many of the same functions as standardization of goods and services; both are essential to a system of mass production and distribution. Scarce and costly time and skill can be devoted to a class of transactions rather than the details of individual transactions."). Doubtless a state could forbid the use of standard contracts in the software business, but we do not think that Wisconsin has done so.
 Transactions in which the exchange of money precedes the communication of detailed terms are common. Consider the purchase of insurance. The buyer goes to an agent, who explains the essentials (amount of coverage, number of years) and remits the premium to the home office, which sends back a policy. On the district judge's understanding, the terms of the policy are irrelevant because the insured paid before receiving them. Yet the device of payment, often with a "binder" (so that the insurance takes effect immediately even though the home office reserves the right to withdraw coverage later), in advance of the policy, serves buyers' interests by accelerating effectiveness and reducing transactions costs. Or consider the purchase of an airline ticket. The traveler calls the carrier or an agent, is quoted a price, reserves a seat, pays, and gets a ticket, in that order. The ticket contains elaborate terms, which the traveler can reject by canceling the reservation. To use the ticket is to accept the terms, even terms that in retrospect are disadvantageous. See Carnival Cruise Lines, Inc. v. Shute, 499 U.S. 585 (1991); see also Vimar Seguros y Reaseguros, S.A. v. M/V Sky Reefer, 115 S.Ct. 2322 (1995) (bills of lading). Just so with a ticket to a concert. The back of the ticket states that the patron promises not to record the concert; to attend is to agree. A theater that detects a violation will confiscate the tape and escort the violator to the exit. One could arrange things so that every concertgoer signs this promise before forking over the money, but that cumbersome way of doing things not only would lengthen queues and raise prices but also would scotch the sale of tickets by phone or electronic data service.
 Consumer goods work the same way. Someone who wants to buy a radio set visits a store, pays, and walks out with a box. Inside the box is a leaflet containing some terms, the most important of which usually is the warranty, read for the first time in the comfort of home. By Zeidenberg's lights, the warranty in the box is irrelevant; every consumer gets the standard warranty implied by the UCC in the event the contract is silent; yet so far as we are aware no state disregards warranties furnished with consumer products. Drugs come with a list of ingredients on the outside and an elaborate package insert on the inside. The package insert describes drug interactions, contraindications, and other vital information - but, if Zeidenberg is right, the purchaser need not read the package insert, because it is not part of the contract.
 Next consider the software industry itself. Only a minority of sales take place over the counter, where there are boxes to peruse. A customer pay place an order by phone in response to a line item in a catalog or a review in a magazine. Much software is ordered over the Internet by purchasers who have never seen a box. Increasingly software arrives by wire. There is no box; there is only a stream of electrons, a collection of information that includes data, an application program, instructions, many limitations ("MegaPixel 3.14159 cannot be used with Byte-Pusher 2.718"), and the terms of sale. The user purchases a serial number, which activates the software's features. On Zeidenberg's arguments, these unboxed sales are unfettered by terms - so the seller has made a broad warranty and must pay consequential damages for any shortfalls in performance, two "promises" that if taken seriously would drive prices through the ceiling or return transactions to the horse-and-buggy age.
 According to the district court, the UCC does not countenance the sequence of money now, terms later. (Wisconsin's version of the UCC does not differ from the Official Version in any material respect, so we use the regular numbering system. Wis. Stat. sec. 402.201 corresponds to UCC sec. 2-201, and other citations are easy to derive.) One of the court's reasons - that by proposing as part of the draft Article 2B a new UCC sec. 2-2203 that would explicitly validate standard-form user licenses, the American Law Institute and the National Conference of Commissioners on Uniform Laws have conceded the invalidity of shrinkwrap licenses under current law, see 908 F. Supp. at 655-66 - depends on a faulty inference. To propose a change in a law's text is not necessarily to propose a change in the law's effect. New words may be designed to fortify the current rule with a more precise text that curtails uncertainty. To judge by the flux of law review articles discussing shrinkwrap licenses, uncertainty is much in need of reduction - although businesses seem to feel less uncertainty than do scholars, for only three cases (other than ours) touch on the subject, and none directly addresses it. See Step-Saver Data Systems, Inc. v. Wyse Technology, 939 F.2d 91 (3d Cir. 1991); Vault Corp. v. Quaid Software Ltd., 847 F.2d 255, 268-70 (5th Cir. 1988); Arizona Retail Systems, Inc. v. Software Link, Inc., 831 F. Supp. 759 (D. Ariz. 1993). As their titles suggest, these are not consumer transactions. Step-Saver is a battle-of-the-forms case, in which the parties exchange incompatible forms and a court must decide which prevails. See Northrop Corp. v. Litronic Industries, 29 F.3d 1173 (7th Cir. 1994) (Illinois law); Douglas G. Baird & Robert Weisberg, Rules, Standards, and the Battle of the Forms: A Reassessment of sec. 2-207, 68 Va. L. Rev. 1217, 1227-31 (1982). Our case has only one form; UCC sec. 2-207 is irrelevant. Vault holds that Louisiana's special shrinkwrap-license statute is preempted by federal law, a question to which we return. And Arizona Retail Systems did not reach the question, because the court found that the buyer knew the terms of the license before purchasing the software.
 What then does the current version of the UCC have to say? We think that the place to start is sec. 2-204(1): "A contract for sale of goods may be made in any manner sufficient to show agreement, including conduct by both parties which recognizes the existence of such a contract." A vendor, as master of the offer, may invite acceptance by conduct, and may propose limitations on the kind of conduct that constitutes acceptance. A buyer may accept by performing the acts the vendor proposes to treat as acceptance. And that is what happened. ProCD proposed a contract that a buyer would accept by using the software after having an opportunity to read the license at leisure. This Zeidenberg did. He had no choice, because the software splashed the license on the screen and would not let him proceed without indicating acceptance. So although the district judge was right to say that a contract can be, and often is, formed simply by paying the price and walking out of the store, the UCC permits contracts to be formed in other ways. ProCD proposed such a different way, and without protest Zeidenberg agreed. Ours is not a case in which a consumer opens a package to find an insert saying "you owe us an extra $10,000" and the seller files suit to collect. Any buyer finding such a demand can prevent formation of the contract by returning the package, as can any consumer who concludes that the terms of the license make the software worth less than the purchase price. Nothing in the UCC requires a seller to maximize the buyer's net gains.
 Section 2-606, which defines "acceptance of goods", reinforces this understanding. A buyer accepts goods under sec. 2-606(1)(b) when, after an opportunity to inspect, he fails to make an effective rejection under sec. 2-602(1). ProCD extended an opportunity to reject if a buyer should find the license terms unsatisfactory; Zeidenberg inspected the package, tried out the software, learned of the license, and did not reject the goods. We refer to sec. 2-606 only to show that the opportunity to return goods can be important; acceptance of an offer differs from acceptance of goods after delivery, see Gillen v. Atalanta Systems, Inc., 997 F.2d 280, 284 n.1 (7th Cir. 1993); but the UCC consistently permits the parties to structure their relations so that the buyer has a chance to make a final decision after a detailed review.
 The district court held that, even if Wisconsin treats shrinkwrap licenses as contracts, sec. 301(a) of the Copyright Act, 17 U.S.C. sec. 301(a), prevents their enforcement. 908 F. Supp. at 656-59. The relevant part of sec. 301(a) preempts any "legal or equitable rights [under state law] that are equivalent to any of the exclusive rights within the general scope of copyright as specified by section 106 in works of authorship that are fixed in a tangible medium of expression and come within the subject matter of copyright as specified by sections 102 and 103". ProCD's software and data are "fixed in a tangible medium of expression", and the district judge held that they are "within the subject matter of copyright". The latter conclusion is plainly right for the copyrighted application program, and the judge thought that the data likewise are "within the subject matter of copyright" even if, after Feist, they are not sufficiently original to be copyrighted. 908 F. Supp. at 656-57. Baltimore Orioles, Inc. v. Major League Baseball Players Ass'n, 805 F.2d 663, 676 (7th Cir. 1986), supports that conclusion, with which commentators agree. E.g., Paul Goldstein, III Copyright sec. 15.2.3 (2d ed. 1996); Melville B. Nimmer & David Nimmer, Nimmer on Copyright sec. 101[B] (1995); William F. Patry, II Copyright Law and Practice 1108-09 (1994). One function of sec. 301(a) is to prevent states from giving special protection to works of authorship that Congress has decided should be in the public domain, which it can accomplish only if "subject matter of copyright" includes all works of a type covered by sections 102 and 103, even if federal law does not afford protection to them. Cf. Bonito Boats, Inc. v. Thunder Craft Boats, Inc., 489 U.S. 141 (1989) (same principle under patent laws).
 But are rights created by contract "equivalent to any of the exclusive rights within the general scope of copyright"? Three courts of appeals have answered "no." National Car Rental Systems, Inc. v. Computer Associates International, Inc., 991 F.2d 426, 433 (8th Cir. 1993); Taquino v. Teledyne Monarch Rubber, 893 F.2d 1488, 1501 (5th Cir. 1990); Acorn Structures, Inc. v. Swantz, 846 F.2d 923, 926 (4th Cir. 1988). The district court disagreed with these decisions, 908 F. Supp. at 658, but we think them sound. Rights "equivalent to any of the exclusive rights within the general scope of copyright" are rights established by law - rights that restrict the options of persons who are strangers to the author. Copyright law forbids duplication, public performance, and so on, unless the person wishing to copy or perform the work gets permission; silence means a ban on copying. A copyright is a right against the world. Contracts, by contrast, generally affect only their parties; strangers may do as they please, so contracts do not create "exclusive rights." Someone who found a copy of SelectPhone (trademark) on the street would not be affected by the shrinkwrap license - though the federal copyright laws of their own force would limit the finder's ability to copy or transmit the application program.
 Think for a moment about trade secrets. One common trade secret is a customer list. After Feist, a simple alphabetical list of a firm's customers, with address and telephone numbers, could not be protected by copyright. Yet Kewanee Oil Co. v. Bicron Corp., 416 U.S. 470 (1974), holds that contracts about trade secrets may be enforced - precisely because they do not affect strangers' ability to discover and use the information independently. If the amendment of sec. 301(a) in 1976 overruled Kewanee and abolished consensual protection of those trade secrets that cannot be copyrighted, no one has noticed - though abolition is a logical consequence of the district court's approach. Think, too, about everyday transactions in intellectual property. A customer visits a video store and rents a copy of Night of the Lepus. The customer's contract with the store limits use of the tape to home viewing and requires its return in two days. May the customer keep the tape, on the ground that sec. 301(a) makes the promise unenforceable?
 A law student uses the LEXIS database, containing public-domain documents, under a contract limiting the results to educational endeavors; may the student resell his access to this database to a law firm from which LEXIS seeks to collect a much higher hourly rate? Suppose ProCD hires a firm to scour the nation for telephone directories, promising to pay $100 for each that ProCD does not already have. The firm locates 100 new directories, which it sends to ProCD with an invoice for $10,000. ProCD incorporates the directories into its database; does it have to pay the bill? Surely yes; Aronson v. Quick Point Pencil Co., 440 U.S. 257 (1979), holds that promises to pay for intellectual property may be enforced even though federal law (in Aronson, the patent law) offers no protection against third-party uses of that property. See also Kennedy v. Wright, 851 F.2d 963 (7th Cir. 1988). But these illustrations are what our case is about. ProCD offers software and data for two prices: one for personal use, a higher price for commercial use. Zeidenberg wants to use the data without paying the seller's price; if the law student and Quick Point Pencil Co. could not do that, neither can Zeidenberg.
 Although Congress possesses power to preempt even the enforcement of contracts about intellectual property - or railroads, on which see Norfolk & Western Ry. v. Train Dispatchers, 499 U.S. 117 (1991) - courts usually read preemption clauses to leave private contracts unaffected. American Airlines, Inc. v. Wolens, 115 S.Ct. 817 (1995), provides a nice illustration. A federal statute preempts any state "law, rule, regulation, standard, or other provision . . . relating to rates, routes, or services of any air carrier." 49 U.S.C. App. sec. 1305(a)(1). Does such a law preempt the law of contracts - so that, for example, an air carrier need not honor a quoted price (or a contract to reduce the price by the value of frequent flyer miles)? The Court allowed that it is possible to read the statute that broadly but thought such an interpretation would make little sense. Terms and conditions offered by contract reflect private ordering, essential to the efficient functioning of markets. 115 S.Ct. at 824-25. Although some principles that carry the name of contract law are designed to defeat rather than implement consensual transactions, id. at 826 n.8, the rules that respect private choice are not preempted by a clause such as sec. 1305(a)(1). Section 301(a) plays a role similar to sec. 1301(a)(1): it prevents states from substituting their own regulatory systems for those of the national government. Just as sec. 301(a) does not itself interfere with private transactions in intellectual property, so it does not prevent states from respecting those transactions. Like the Supreme Court in Wolens, we think it prudent to refrain from adopting a rule that anything with the label "contract" is necessarily outside the preemption clause: the variations and possibilities are too numerous to foresee. National Car Rental likewise recognizes the possibility that some applications of the law of contract could interfere with the attainment of national objectives and therefore come within the domain of sec. 301(a). But general enforcement of shrinkwrap licenses of the kind before us does not create such interference.
 Aronson emphasized that enforcement of the contract between Aronson and Quick Point Pencil Company would not withdraw any information from the public domain. That is equally true of the contract between ProCD and Zeidenberg. Everyone remains free to copy and disseminate all 3,000 telephone books that have been incorporated into ProCD's database. Anyone can add sic codes and zip codes. ProCD's rivals have done so. Enforcement of the shrinkwrap license may even make information more readily available, by reducing the price ProCD charges to consumer buyers. To the extent licenses facilitate distribution of object code while concealing the source code (the point of a clause forbidding disassembly), they serve the same procompetitive functions as does the law of trade secrets. Rockwell Graphic Systems, Inc. v. DEV Industries, Inc., 925 F.2d 174, 180 (7th Cir. 1991). Licenses may have other benefits for consumers: many licenses permit users to make extra copies, to use the software on multiple computers, even to incorporate the software into the user's products. But whether a particular license is generous or restrictive, a simple two-party contract is not "equivalent to any of the exclusive rights within the general scope of copyright" and therefore may be enforced.
 REVERSED AND REMANDED