The judgment that an artist is great always rests on assessments of the work the artist has produced  A series of great works is the only indicator of greatness
Ttherefore, to say that an artist is great is just to summarize the quality of his or her known works, and the artist' s greatness can provide no basis for predicting the quality of the artist' s unknown or future works
The only way of knowing whether someone has a cold is to observe symptoms. Thus, when a person is said to have a cold, this means only that he or she has displayed the symptoms of a cold, and no prediction about the patient's future symptoms is justified.