Simon Armitage's "Snow Joke" raises the issue of how something becomes a sign of something else, of how something becomes evidence. "On Miles Platting Station," the next poem in Armitage's Zoom!, concludes with an explicit mention of a different kind of evidence:
Somewhere beyond that the water in Shiny Brook
spills like a broken necklace into our village.
The police are there again: boxhauling the traffic,
adjusting the arc-lights. They have new evidence tonight
and they lift it from behind the windbreak, cradle it
along their human chain and lower it carefully down
This makes me wonder about evidence: when is something evidence, and when is it not? How does something that is not evidence turn into evidence? I assume there are theoretical discussions of this in criminology, the philosophy of science, and philosophy in general (not to mention medicine and psychology, where the issue is what a symptom is).
But in the reading of poetry, and in the reception of art in general, everything in the work is evidence; that is, everything is ready to be understood as a sign of something else, as a symptom. Every feature of a work of art is always both itself and, by virtue of being in a work of art, something more—if nothing else, it is evidence of that surplus, that excess, an excess created by the identification of art as art, by the recipient's readiness to understand the object at hand as art.