" While there are certainly informational spillovers as ideas move from person to person, it is hard to see why in most instances they are not priced. Although it is possible to imagine examples such as the wheelbarrow where an idea cannot be used without revealing the secret, relatively few ideas are of this type. For copyrightable creations such as books, music, plays, movies and art, unpriced spillovers obviously play little role. A book, a CD or a work of art must be purchased before it can be used, and the creator is free to make use of his creation in the privacy of his home without revealing the secret to the public at large. Similarly with movies or plays. In all cases, the creation must effectively be purchased before the “secret” is revealed. "