A legal system providing a property right in a human creative effort rests on two fundamental bases: the standards for establishing the right and the scope of the right. Copyright law requires that an author's work be original, and it confers on the author exclusive rights against unauthorized copying, distribution and other activity of works that are substantially similar in expression to the protected work. Similar requirements are imposed by trademark law for product and service identification symbols and by patent law for inventions.

To define the scope of an intellectual property right, legal systems have adopted one of two approaches. First, protection scope can be defined by a direct comparison of the creator's work and an accused work. Copyright and trademark law follow this approach for determining protective scope, that is, infringement. Consider a copyright example. An author's work, a play ‘Romeo and Juliet’, portrays the travails of young lovers from contrasting family cultures in Verona, Italy, centuries ago. An unauthorized accused work, a motion picture ‘West Side Story’, portrays a similar story set in twentieth-century New York. The author's copyright is infringed if the accused work is judged to be substantially similar in expression to the protected work. For trademark law, the inquiry is analogous. One company adopts a trademark ‘Lexis’ for legal data bases. Later, another company uses ‘Lexus’ for luxury automobiles.