Non-restrictive prepositional phrase starting with "of"

Question

1. Recently I've visited an art gallery and happened to come across a masterpiece , of a woman the artist had loved for a long time.

2. Recently I've visited an art gallery and happened to come across a masterpiece of a woman the artist had loved for a long time.

Would there be any difference between them in meaning, just merely only for that comma inserted right before "of"?

I think there is! and the meaning is, on the whole, different to each other.

In number 1, "I" seem to be not sure whether it's really a woman the artist had loved, but just guess it would be a woman, having seen the masterpiece, or it couldn't have been seen as a woman even at all because it was drawn so abstactically that "I" didn't recognize whether the artist drew it about a woman or not.

But on the other hand, In number 2, "I" seem to be sure that it's a masterpiece of a woman and the masterpiece is definitely of a woman.

I think this difference could be found out in these following sentences as well.

3. This final portrayal, of Stalin, does no credit to the author.
4. This final portrayal of Stalin does no credit to the author.

In number 3, we can't be sure whether this final portrayal is really of Stalin or not, but in number 4, we can be sure that it is of Stalin.

Answer 1

The use of commas has nothing to do with the certainty of the statement.

In the first sentence, you are talking about a masterpiece. It just happens to be of a woman. In the second sentence, you are talking about a masterpiece that is defined by the fact that it is of a woman—the fact that it's about a woman is key to understanding the entire sentence.

In both cases, the subject of the painting still is a woman. That remains a definite fact. But it's not an important fact in the first sentence.

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The third and fourth sentences can be interpreted similarly. Both portrayals definitely are of Stalin, but it's only in the fourth sentence where that fact is directly relevant to the sentence. In the third sentence, that it's a portrayal of Stalin specifically is irrelevant to the credit (or lack of it) given to the author. Whereas in the fourth sentence, that it's a portrayal of Stalin is directly relevant.