Professional art critics are expected to have a keen eye for art and a thorough knowledge of art history. Knowledge, however, provides no guarantee that a critic will know if a work of art, an exhibition, or an artist will stand out in history as "great".

Many now famous and celebrated artists were not recognized by the art critics of their time, often because their art was in a style not yet understood or favored. Conversely, some critics, called militant critics have helped to explain and promote new art movements.