An artist produces an effect in virtue of the distinctness with which he sees the objects he represents, seeing them not vaguely as in vanishing apparitions, but steadily, and in their most characteristic relations. To this Vision he adds artistic skill with which to make us see. He may have clear conceptions, yet fail to make them clear to us: in this case he has imagination, but is not an artist. Without clear Vision no skill can avail. Imperfect Vision necessitates imperfect representation; words take the place of ideas.

The Principles of Success in Literature (1865)