It is often difficult to determine what counts as plagiarism, because groups of people often work on projects as a team. For example, it may be selfish for celebrities not to credit their ghostwriters, but this is not considered plagiarism, because ghostwriters are members of the publisher’s staff. In addition, most new ideas are based on combinations of old ideas. In an academic context, students are taught to analyze the sources of their ideas. Therefore, they are expected to provide citations for any direct quotations, paraphrases, and important ideas that are taken from another published author. Failure to do so is plagiarism. Because what a plagiarist steals—credit—is intangible, punishment is usually informal and is based on ethical or social factors. Students who plagiarize are penalized by their schools because teachers want them to learn not to steal in any situation. Professors who plagiarize have violated the social norms of scholarship and therefore their reputations as scholars. In the world of commercial publishing, however, when a plagiarizer robs an original author of profit as well as credit, plagiarism is grounds for a civil lawsuit, and legal penalties can include financial compensation of the injured party.