“The Constitution . . . affords a lesser protection to commercial speech than to other constitutionally guaranteed expression.” Commercial speech is “speech that proposes a commercial transaction.” That books and films are published and sold for profit does not make them commercial speech; i.e., it does not “prevent them from being a form of expression whose liberty is safeguarded [to the maximum extent] by the First Amendment.” Commercial speech, however, may be banned if it is false or misleading, or if it advertises an illegal product or service. Even if fits in none of these categories, the government may regulate it more than it may regulate fully protected speech.