Whenever an artist endowed with both a high level of artistic skill and a high degree of creativity combines these two abilities in the process of creating an artwork, the resulting product is a great work of art. Moreover, no work of art can be great unless both of these elements are combined in its execution. Thus, great works of art are necessarily rare.
A high degree of creativity and a high level of artistic skill are seldom combined in the creation of a work of art is an assumption required by the argument.