Truth to nature -- in music, to the ever-changing nature of emotions and moods -- and distinctiveness of personality, seem to be the levels on which artworks achieve uniqueness. But let us recall that this is a perceived uniqueness, an aspect of the text rather than of the phenomenon. The most miserably routine composition exercise of an untalented student is of course unique in the phenomenal sense, but it does not project uniqueness; it possesses uniqueness as a rational quality, not as a textual quality. This demonstrates that the originality and specialness of artworks are products of the author's devising, not categorical realities. And since textual qualities are also semiotic qualities, it may be possible to investigate these kinds of uniqueness (truth to life, and the communication of personality) in terms of signs and codes.
But things are not as simple as they have so far seemed. Modern critical theory adds a radical gloss to the views of Lord David Cecil. The "real life" which is reflected by the eloquent artwork is not an external feature, but an inner genre, part of the life of culture and literature; it is itself a system of signs, a textual feature. The authorial personality, too, delineated so strongly in the novels of George Eliot, is in truth a product of the text, not a historical reality. In researching the projected uniqueness of the artistic work, we should look, not merely for unique features, but for signs of genre and signs of subjectivity: indicators of the mythemes and culturemes which constitute our perception of life, and traces of a portrayed or implied author, orator of the text at hand.
Artistic verisimilitude is truth, then, not to nature but to genre; and the authorial personality is a feature, not of the author but of the text. Consequently, our argument may now proceed out of the field of analytical semiotics into that of textual semiotics.
If the uniqueness of the artwork is a textual feature, then it may, after all, be approachable in terms of conventional signs. A sign motivated by simple realism (the older view of verisimilitude) conforms to ratio difficilis, in Eco's language (Eco: 1976, 183-187). But Eco implies that most examples of ratio difficilis (in which the sign is simply mapped on to the features of the object, without the intervention of any rule) conceal, shadow or generate instances of ratio facilis (in which the relation of sign and object is governed by learned rules and codes).