Gauss and I recently had a friendly conversation where he pointed out that the 3.5 rules are much clearer on Knowledge: Arcana than the Pathfinder PRD:
20 + spell level Identify a spell that’s already in place and in effect. You must be able to see or detect the effects of the spell. No action required. No retry.
Knowledge DC Checks: Identify a spell effect that is in place Arcana 20 + spell level
I accepted Gauss' assertion that this meant that Detect Magic and a Knowledge: Arcana roll was insufficient to determine that a succubus had been polymorphed, and considered the case closed.
My co-GM vehemently disagrees. He feels that the Paizo staff intentionally removed the "You must be able to see or detect the effects" so as to make it easier for PCs to determine what buffs an enemy has up, etc. (Assuming they get the 3 full rounds of Detect Magic.)
I'd love opinions. I have the luxury of examining a polymorphed succubus using Detect Magic for 3 rounds, and I make a DC 25 Knowledge: Arcana check.
What do I learn? Solely that she has a transmutation spell on her, or that she has Polymorph on her?
I have no fish to fry in this debate. I liked Gauss' reasoning. But as I said, my co-GM disagrees, so I'm throwing the question to the wolves, and wallowing in my own metaphors...