"Aesthetics is to artists as ornithology is to birds." See why Barnett Newman's quote is right (though it doesn't have to be).
Nelson Goodman (1906-1998) was an American analytic philosopher who wrote on epistemology, logic, and aesthetics. But aesthetics has always been the red-headed stepchild in philosophy, never gaining acceptance in the broader field and perhaps more importantly never gaining any traction with those actually associated with art. A reading straight from Goodman's text will show you why.