Why didn't Dumbledore realise that Moody had been replaced?

Question

Throughout the books we are led to believe that Dumbledore is not only incredibly smart and powerful, but also very astute. He has a way of predicting what people will do and how they will react. He could read Voldemort better than Voldemort himself. He could feel magic and knew when spells had been used, yet in Goblet of Fire it completely escapes his attention that Moody is, in fact, not Moody at all, even though the original Moody was a close friend of Dumbledore. We are led to believe that Polyjuice Potion only changes a person's appearance, yet Barty Crouch Jr. seemed to have been able to take on the exact personality of Moody and to fool one of the greatest wizards of all time.

Why didn't Dumbledore realise that Moody had been replaced?

Answer 1

Dumbledore isn't as insightful as we are led to believe.

Remember, we're given everything through Harry's eyes--the eyes of an orphan who hero-worships the first authority figure in his life who treats him kindly. Additionally, it is in Dumbledore's best interests to create the illusion of competence he lacks. Later in the series we learn that he made some very glaring and obvious mistakes, and things work out largely through luck and factors he never anticipated... although he often takes credit for those, too.

Dumbledore hadn't seen Moody regularly, maybe even not since shortly after Harry's birth.

Mad-Eye is described as an "old friend" of Dumbledore's who "doesn't trust anyone anymore" and had to be cajoled and prodded to un-retire. While it's not concrete, it seems very reasonable that between Moody's paranoid retirement and Dumbledore's running a school and a sprawling power base, neither of them had much time for or interest in casually dropping by for tea.

At any rate, Dumbledore had a lot on his mind (what with hosting a lethal set of competitions and two unscrupulous rival schools, as well as other pressures we only later on find out he was dealing with) at the time. Moody's paranoia seemed more justified than ever, and Dumbledore was probably just happy to have the man there--and maybe a little overconfident in his old friend's ability to keep himself safe.

Answer 2

Additional Magical Support

We know that Barty Crouch was an extremely powerful wizard from his ability to cast a Confundus Charm strong enough to confuse the Goblet of Fire into allowing Harry to be named as a fourth contender for the Tri-Wizard cup. Given that, there is nothing that would have prohibited Barty from being able to use additional magical charms beyond simply the Polyjuice Potion which disguised his physical appearance even if not mentioned. E.g. perhaps he had a light Confundus Charm in operation around his body acting something like a cloaking device in addition to the Polyjuice Potion.

Additional Source Material Available:

Barty had access to the real Mad-Eye Moody locked up. He could have easily to ask him about his habits and practices in order to properly impersonate him. Or even torture him into revealing those habits to him. From what we see of Barty as a Defense Against the Dark Arts instructor, he was an expert on the forbidden curses both in casting and resisting. The real Mad-Eye looked pretty shabby when we first get to see him. He was clearly not being well cared for as a prisoner. Even restricting food and water can be a powerful motivator. In other examples of Polyjuice use (such a fun word play rhyme:-)) the users did not have ready access to the person(s) whom were being imitated. Barty did.

Natural Human Tendencies

Finally, we know that Barty DID make some mistakes in his actions (e.g. his tongue flicking out - at least in the movies). However, we humans (and I would think including Witches and Wizards) rely strongly on sight in identifying others. I have to believe even wizards and witches would be unlikely to constantly run around expecting someone they visually see as person A to really be person B. To do otherwise would mean someone would have to almost act in a paranoid fashion questioning everyone's identify all the time. We see several other times in canon when a person operating under Polyjuice Potion makes odd mistakes in front of others yet, nobody thinks to suspect that they are not who they appear to be. E.g. when Harry and Ron imitate Crabbe and Goyle in front of Draco in their second year. Or, when Harry, Ron and Hermione slip into the Ministry of Magic using Polyjuice Potion.

This line of thinking is supported from the Harry Potter Wikia site:

Harry Potter Wiki - PolyJuice

"The lack of suspicion in anyone in all these incidents leads one to the understanding that Polyjuice Potion is very uncommon. Granted, Severus Snape knew someone was stealing the ingredients from his cupboards and suspected Harry Potter, but that is more indicative of Snape's eagerness to blame Harry for anything than any actual guilt."

Origin of Source Material Being Imitated

Remember Moody's moniker was "Mad-Eye". He was expected to be a bit daft as our British compatriots might say. That could easily help support explaining why others didn't immediately tip to potentially odd behaviors performed by Barty while acting as Moody. Even Dumbledore.

Answer 3

In addition to the top-voted answer here, which is brilliantly written, Barty Crouch Jr. explains in the chapter 'Veritaserum' of Goblet that he had been forcing information out of the real Mad-Eye Moody in order to learn how to act exactly like him - right down to Moody's predilection for drinking from a hip-flask. His sayings, his mannerisms, and even, I suppose, Moody's relationship and history with Dumbledore, would have been essential knowledge for Crouch to master. With an actor that good and a part so meticulously researched, it's fair to say that he could fool even Dumbledore.

The actual quote from the book:

Then I packed up Moody's clothes and Dark detectors, put them in the trunk with Moody, and set off for Hogwarts. I kept him alive, under the Imperius Curse. I wanted to be able to question him. To find out about his past, learn his habits, so that I could fool even Dumbledore. I also needed his hair to make the Polyjuice Potion.
-Harry Potter and the Goblet of Fire, Chapter Thirty-Five (Veritaserum) - Page 445.

Answer 4

Because of how flawless Crouch's impersonation of Moody was. The only time he acted out of Moody's character was when he took Harry out of Dumbledore's sight in the aftermath of Voldemort's return, and Dumbledore immediately noticed it as such and realized he was an imposter, which is how he saved Harry's life (again) at the end of Goblet of Fire. So it wasn't that Dumbledore lacked sight, it was just that Crouch did a perfect job impersonating Moody.

Answer 5

oh Dumbledore knew he knew as soon as Madeye's house was attacked. The Order is sworn to protect Harry and his allies.

1. Each of them must speak in code to Harry and his allies and only Harry knows the proper counter code to confirm they are not an impostor. The fake Madeye did not give the countersign every time he was with Harry after Order of the Phoenix this is mandatory you can not enter a dwelling or approach Harry unless you say the password because Death Eaters can use polyjuice and so can the Order and Harry.
2. No one in the Order will harm Harry or his allies. The fake Madeye lured Harry 4 times each time placing him at risk.
3. An Order Member will never disobey a direct order if it is issued by Dumbledore, Harry, the Marauders, or Hogwarts Staff. The fake Madeye lured Harry out of the stadium to kill him and he did not tell Dumbledore or any Order member where he was going that right there is a red flag and Dumbledore was alerted immediately.

Once they entered the office the fake Madeye told Harry he set him up and he was going to kill him because he escaped his master before he could Harry looked at the looking glass and once Dumbledore, McGonagall, and Snape were in range Harry drew his wand, Dumbledore blew the door open, and the four of them cast their stunning spells.

Dumbledore explained to Harry everything: the robbery, Jr. impersonating Madeye, the Polyjuice Potion, the disabled dark detectors, and how Jr. broke character when he disobeyed a direct order. Dumbledore then unlocked the trunk and there in the bottom in a holding cell was Madeye. Minutes later Jr. turned back into himself and Snape and Dumbledore interrogated him with McGonagall serving as the recorder. Jr. confessed everything and once the Truth Serum wore off Jr. was tied up and McGonagall was placed on guard.

Harry and Dumbledore went up to his office and debriefed Sirius and Harry once the debriefing was complete Harry was sent to the hospital to rest until the intelligence briefing. During this time Fudge arrived and he brought the Dementors with him. Fudge entered the office, undid Jr. bounds, burned the statement with his wand, and sent the Dementor in to kill Jr. to dispose of the evidence.

Harry woke up to Snape and McGonagall shouting at Fudge for what he did. Dumbledore rebuked Fudge and Sirius growled at him with Snape telling Fudge "You want proof? (pulls up his arm) there's the Dark Mark I felt it burn all night so did Karkaroff." After Fudge left Dumbledore sealed the room, Hermione caught Rita and placed her in a unbreakable soundproof bell jar and placed her in her purse, and with the distractions out of the way he started the briefing.

Sirius returned to his real form and Dumbledore sent him off first, Snape left second he had a secret mission, Molly was the next to leave after she and Madam Pomfrey nursed Harry back the health, Bill was the next to leave and he took Fleur with him, Dumbledore told Fleur to apply for duel citizenship and both of them had a job to do they had to guard the bank, and Hagrid was the last to leave he had to get Grawp and try to convince the giants to join their side but Macnair got to them first. And with that The Order was founded and once Madeye was back on his feet he became their leader.

Answer 6

Dumbledore knew Moody was not Moody and just wanted to see where it would go. You could say that he knew it was inevitable that Voldemort was to return and figured it would make Harry stronger if Harry was able to get close to some of Voldemort's insiders. Ultimately Dumbledore felt that he could keep Harry safe and allowed Harry to develop his skills.