For example, the Macintosh interface was based on ideas tried previously by Xerox and SRI, and before that by the Stanford Artificial Intelligence Laboratory. This evolutionary process resembles the creation of folk art rather than the way symphonies, novels or films are made. The advances that we ought to encourage are most often small, localized changes to what someone else has done. If each interface has an owner, it will be difficult to implement such ideas. Even assuming the owner will license the interface that is to be improved, the inconvenience and expense would discourage all but the most determined.
Users often appreciate small, incremental changes that make programs easier or faster to use.
This means changes that are upwards compatible, or affect only part of a well-known interface. Thus, on computer keyboards, we now have function keys, arrow keys, a delete key and a control key, which typewriters did not have. But the layout of the letters is unchanged. However, such partial changes as this are not permitted by copyright law. If any significant portion of the new interface is the same as a copyrighted interface, the new interface is illegal.