A few days back I asked how Dumbledore could not have known Peter was a spy. The discussion went on for quite a while, and many wonderful answers were proposed, so here, have a summary. I've left out the theories from my original post, though those were debated too. It was a long thread!
He knew.
-Dumbledore did know Peter was a spy, but didn't have enough proof, or thought he could Legilimens information about Voldemort from Peter without his knowing. He thought the final decision was that Sirius would be Secret-Keeper, so he was not worried for the Potters' immediate safety. [link]
-He knew or suspected that Peter had been contacted by Voldemort, and was trying to give him an opportunity to prove his moral strength. Oops. [link]
-He has foreknowledge of what will happen because he is a time traveler, and allowed Peter to betray the Potters because he knew it would ultimately be necessary. [link]
He didn't know.
-The problem was hubris -- considering that one of his Gryffindors might have turned would have meant admitting his own fallibility. [link]
-Dumbledore avoided using Legilimency on the Order members, either out of respect for them, or because he didn't want them to become disgruntled. [link] [link]
-Dumbledore is not as great a Legilimens as we think, and/or it was because of Peter's betrayal that he became a Legilimens in the first place. [link] [link]
Trick question.
-There was nothing for Dumbledore to find out -- Peter turned traitor not long before the Potters died. [link]
Many thanks to everyone who contributed their thoughts. Damn, I love fandom.
He knew.
-Dumbledore did know Peter was a spy, but didn't have enough proof, or thought he could Legilimens information about Voldemort from Peter without his knowing. He thought the final decision was that Sirius would be Secret-Keeper, so he was not worried for the Potters' immediate safety. [link]
-He knew or suspected that Peter had been contacted by Voldemort, and was trying to give him an opportunity to prove his moral strength. Oops. [link]
-He has foreknowledge of what will happen because he is a time traveler, and allowed Peter to betray the Potters because he knew it would ultimately be necessary. [link]
This is an aspect of the Knight2King theory, which postulates that Dumbledore is Ron Weasley, gone back in time. K2K is always neat to look at, though it may be slightly beyond the scope of this discussion.-He was simply trying to allow the terms of the prophecy to be fulfilled. [link]
He didn't know.
-The problem was hubris -- considering that one of his Gryffindors might have turned would have meant admitting his own fallibility. [link]
-Dumbledore avoided using Legilimency on the Order members, either out of respect for them, or because he didn't want them to become disgruntled. [link] [link]
-Dumbledore is not as great a Legilimens as we think, and/or it was because of Peter's betrayal that he became a Legilimens in the first place. [link] [link]
Trick question.
-There was nothing for Dumbledore to find out -- Peter turned traitor not long before the Potters died. [link]
Requires that we disbelieve Sirius's assertion that Peter was passing information to Voldemort for a year before the Potters died, and demands another explanation for where that information was leaking from.-Dumbledore is an allegorical-type deus ex machina. Discussing his motives and abilities in realistic terms is the wrong level of analysis for his character. [link]
This is a fascinating topic, and I encourage you all to take a look at whatdonnaimmaculata had to say about it.
ptyx also called Dumbledore an "impossible character" earlier in the discussion, which gets at the same idea.
Many thanks to everyone who contributed their thoughts. Damn, I love fandom.