Why didn't Dumbledore say at the trial that he'd given Harry permission?

Question

We know from the conversation in the beginning of Half-Blood Prince that the headmaster could allow students to do magic outside Hogwarts.

‘Keep your wand at the ready, Harry,’ he [Dumbledore] said brightly.

'But I thought I’m not allowed to use magic outside school, sir?’

‘If there is an attack,’ said Dumbledore, ‘I give you permission to use any counter-jinx or -curse that might occur to you.

So why didn't they use this defense at the trial in Order of the Phoenix? They wouldn't have had to bring Mrs. Figg then. Dudley already knew about magic, so the only valid charge would be underage magic, and Dumbledore had the power to allow that. Why mention the Dementors at all?

Answer 1

In addition to excellent reasons in @Richard's answer, there are 3 other ones:

1. The HBP quote was (obviously) post-OoTP; by that point, there was no high risk of MoM going after Harry. Rufus Scrimgeour may have disagreed with Dumbledore over involving Harry, but he didn't have Fudge's animosity to Harry. And Ding Dong The Evil Witch Is DeadUmbridge was out of action.

2. More importantly, there's no canon evidence that Dumbledore was within his legal rights to permit Harry to do magic outside Hogwarts in the first place for an entire summer.

   If you pay close attention, that "I give you permission" line in HBP you quoted was very specifically aimed to Harry's outing with Dumbledore, NOT a general "whenever you feel like it".

   Which means that, had Harry done magic, Dumbledore could have claimed that he was the one who did it, not Harry. Given point #1, it's possible that would have been enough of a cover.

3. Even if it WAS within Dumbledore's legal right to do so; claiming that he used that right during the Fudge trial would simply give Fudge more reasons to be paranoid about Dumbledore aiming to take power from him. And if they found out that he lied about it, he'd probably end up arrested for perjury.

Answer 2

Dumbledore's motivation is pretty complex but there's a few good reasons why he wouldn't say that he'd given Harry permission to perform magic outside of Hogwarts;

It's a lie that he can't back up

Although Dumbledore doesn't seem to have much compunction against lying to (or concealing things from) the Ministry of Magic, they may ask him to back up his assertion with some sort of permission slip or proof under magical oath. Since he obviously can't provide this, he may get Harry into more trouble than he's already in.

He doesn't know what Harry is going to say (or has already said)

Dumbledore doesn't arrive until a few minutes after Harry's trial has started. If his lie contradicts something that Harry has already said, he may cause both of them very severe difficulty.

The trial serves a deeper purpose.

Dumbledore is using the trial to highlight (to the wider public) that the Ministry has started making bad decisions since he was asked to leave their ruling council, the Wizengamot

"And you certainly seem to be making many changes, Cornelius. Why, in the few short weeks since I was asked to leave the Wizengamot, it has already become the practice to hold a full criminal trial to deal with a simple matter of underage magic!"

A few of the wizards above them shifted uncomfortably in their seats. Fudge turned a slightly deeper shade of puce. The toadlike witch on his right, however, merely gazed at Dumbledore, her face quite expressionless.

The trial allows him to see who's still on his side at the Ministry;

Fudge raised his hand; so did half a dozen others, including the witch on his right and the heavily-moustached wizard and the frizzy-haired witch in the second row. Fudge glanced around at them all, looking as though there was something large stuck in his throat, then lowered his own hand. He took two deep breaths and said, in a voice distorted by suppressed rage, ‘Very well, very well … cleared of all charges.’

‘Excellent,’ said Dumbledore briskly, springing to his feet, pulling out his wand and causing the two chintz armchairs to vanish. ‘Well, I must be getting along. Good-day to you all.’

Answer 3

The important thing to note here is that the trial wasn't standing because Harry had performed magic in front of a muggle, and more so because the ministry wanted to defame him after the incidents at the end of GoF. In reality, even underage wizards are allowed to use magic if under threat, as mentioned in this excerpt from the trial:

“Of course we are,” said Dumbledore, “but the presence of dementors in that alleyway is highly relevant. Clause seven of the Decree states that magic may be used before Muggles in exceptional circumstances, and as those exceptional circumstances include situations that threaten the life of the wizard or witch himself, or witches, wizards, or Muggles present at the time of the —” - Order of The Phoenix, CH8.

Harry did NOT need any permission to perform magic if his or anyone else's life was under threat. The entire trial held only because Fudge and several members of the Jury were NOT convinced that there were any dementors in the first place, and they wanted a reason to prosecute Harry. Also, while Umbridge had in fact sent those Dementors, she was obviously not going to accept this in front of the Ministry of Magic, and hence played along that she did not believe Harry's story either. Dumbledore could not have said anything to change that, as he very much tried to. That is why it was only Mrs. Figg's witness that saved Harry.

Answer 4

Consider this passage from Chapter 31, “The Lost Prophecy” of Order of the Phoenix:

“More recently,” said Dumbledore, “I became concerned that Voldemort might realize that this connection between you exists. Sure enough, there came a time when you entered so far into his mind and thoughts that he sensed your presence. I am speaking, of course, of the night when you witnessed the attack on Mr. Weasley.”

“Yeah, Snape told me,” Harry muttered.

“Professor Snape, Harry,” Dumbledore corrected him quietly. “But did you not wonder why it was not I who explained this to you? Why I did not teach you Occlumency? Why I had not so much as looked at you for months?”

Harry looked up. He could see now that Dumbledore looked sad and tired.

“Yeah,” Harry mumbled. “Yeah, I wondered.”

“You see,” continued Dumbledore heavily, “I believed it could not be long before Voldemort attempted to force his way into your mind, to manipulate and misdirect your thoughts, and I was not eager to give him more incentives to do so. I was sure that if he realized that our relationship was — or had ever been — closer than that of headmaster and pupil, he would seize his chance to use you as a means to spy on me. I feared the uses to which he would put you, the possibility that he might try and possess you. Harry, I believe I was right to think that Voldemort would have made use of you in such a way. On those rare occasions when we had close contact, I thought I saw a shadow of him stir behind your eyes. … I was trying, in distancing myself from you, to protect you. An old man’s mistake …”

Dumbledore was intentionally being cool toward Harry for the entire book, because he was worried that if Voldemort learned of their relationship (which was much closer than that of a typical headmaster and pupil) then Dumbledore and Harry would be endangered. If Dumbledore had walked into Harry’s hearing and spun some yarn about how he had given Harry permission to do magic outside of school, however, it would have been obvious to everyone that their relationship was unusual.

And that’s if he hadn’t been caught in the lie—if he had, the fact that he perjured himself to protect Harry would have indicated an even more unusual relationship! (I think the other answers have already addressed the logistical problems of Dumbledore lying.) During the hearing, Dumbledore intentionally threw Harry under the bus because he judged that Harry’s potential punishment would still be less damaging than revealing their relationship to Voldemort.

Answer 5

‘If there is an attack,’ said Dumbledore, ‘I give you permission to use any counter-jinx or -curse that might occur to you.

From here we know, the permission is 'on' only in dangerous situation

While in the eye of MoM, Harry is no where near such a situation, because there are only him and a muggle (Dudley).

I think that's the reason they need to mention the dementor, which is the appearance not known by MoM. If they did not mention it, like you said, Harry would be charged with underage magic, which would lead to being expelled from hogwarts, because the MoM has on record that Harry already once did magic in front of muggles in The Chamber of Secrets.