If a Forgery Looks Identical, What Still Makes It Different?

Imagine two oil paintings whose colours, brushwork and cracks cannot presently be told apart. One was made by the original artist; the other was copied later. If looking at them feels exactly the same, why would a museum still treat them as different works?

In Languages of Art, Nelson Goodman distinguishes autographic from allographic arts. A painting's authenticity depends on a particular history of production: however accurate a copy may be, it is not that act of making. A musical work, by contrast, is often specified through a score. Different ensembles can produce valid instances without pretending to be the first performance. The distinction does not sort every art neatly. It shows that artistic identity may depend on an object's provenance in some cases and on repeatable symbolic rules in others.

The difference cannot be reduced to market price. Learning that a painting was made by the original artist during a particular investigation can alter how we understand a hesitant stroke, a material choice and the work's relation to other works. A copyist may display remarkable skill but has performed a different action. Deception is a further issue: a copy honestly labelled as such is not posing as an original, yet it remains a copy.

My judgement is that indistinguishable appearance does not require identical value. Aesthetic experience includes visible form, but it can also include who made the work, what problem they faced and how the object entered history. Authenticity is not a substitute for quality, however. Provenance can change a work's identity without making a dull painting good.

https://plato.stanford.edu/entries/goodman-aesthetics/