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 viruses that cause colds are not all the same, and they differ in their effects. Ttherefore, although it may be certain that a person has a cold, it is impossible to predict how the cold will progress.