Uniform Metaphor: A language should be designed around a powerful metaphor that can be uniformly applied in all areas.
Examples of success in this area include LISP, which is built on the model of linked structures; APL, which is built on the model of arrays; and Smalltalk, which is built on the model of communicating objects. In each case, large applications are viewed in the same way as the fundamental units from which the system is built.