Question:
Can you have aesthetic interest in a portrait painting just for its subject as in a photograph?
I don't think that it is an impossibility to have an aesthetic interest in a portrait for its subject as Scruton says you do with a photograph. However, there is so much more to a portrait painting than just its subject which would make it hard to have aesthetic interest only in the subject. Take the subject out of the portrait painting and your aesthetic feeling may go away. For example take Albrecht Durer's Self Portrait from the Northern Renaissance. There is an aerial view seen in the window which gives the painting a sense of depth. Although Durer is the main focus, exclude the window, take him out of the portrait and you just have him. The aerial view provides more interest in the photo beyond him being the subject. The detail of the curls in his hair and the planned placement of each fold of the clothing; you can't get that from taking a photograph of the subject. It’s so precise that the thought behind it was very much intentional.
Albrecht Durer Self Portrait 1498
