Why wasn't Peter Pettigrew bound with an Unbreakable Vow?

Question

Peter was the secret-keeper for the Potters, so wouldn't it make sense to bind him with an Unbreakable Vow so that he could not reveal it? Is there any canonical information regarding this?

Answer 1

In order to answer this question, we need to understand what a Fidelius Charm is and what an Unbreakable Vow is.

Flitwick explains in PoA that the Fidelius Charm is

‘An immensely complex spell,’ he said squeakily, ‘involving the magical concealment of a secret inside a single, living soul. The information is hidden inside the chosen person, or Secret-Keeper, and is henceforth impossible to find – unless, of course, the Secret-Keeper chooses to divulge it. As long as the Secret-Keeper refused to speak, You-Know-Who could search the village where Lily and James were staying for years and never find them, not even if he had his nose pressed against their sitting-room window!’

What about an Unbreakable Vow?

“An Unbreakable Vow?” said Ron, looking stunned. “Nah, he can’t have. . . . Are you sure?”

“Yes, I’m sure,” said Harry. “Why, what does it mean?”

“Well, you can’t break an Unbreakable Vow. . . .”

“I’d worked that much out for myself, funnily enough. What happens if you break it, then?”

“You die,” said Ron simply.

Note that in both cases Peter Pettigrew could have divulged the secret. The only difference is that in the second case he would have died.

Now, think about it. Assume that Pettigrew, while bounded by an Unbreakable Vow, tells Voldemort about the secret (we don't know if Imperiused people can be forced to break a Vow, but maybe Voldemort could have convinced Pettigrew that he was such a powerful wizard that he could have undone the Vow). He dies, but Voldemort can still kill Lily, James, and Harry.

As you can see, an Unbreakable Vow offers no advantage with respect to a "simple" Fidelius Charm, except the death of the traitor, which is not only morally dubious when dealing with a friend - remember that James wouldn't have killed Pettigrew, as Harry says in PoA, and that James considered it essential to trust his friends - but also "useless," in that it doesn't prevent other deaths.

Answer 2

From their perspective, there's no benefit

Consider what an Unbreakable Vow offers, from a security perspective: the purpose would be to make it very painful for Pettigrew to divulge the secret he was entrusted with; if he tells anyone, he dies.

Now consider the circumstances where he might divulge the secret:

• Under torture. Sufficient torture might just be painful enough that he would welcome death, just to make the pain stop. But it's moot anyway, because he can't be forced to divulge the secret under torture; we learn as much from Pottermore:

  [T]he secret cannot be forced, bewitched or tortured out of a Secret Keeper who does not wish to give up their secret; it must be given voluntarily

  ^{Pottermore Secret Keeper}

  So an Unbrekable Vow offers no benefit in this scenario.

• Under the influence of the Imperius Curse. In theory, we might expect that a Death Eater could use the Imperius Curse to just make Pettigrew divulge the secret, but there are two problems with this. First, it assumes that logical arguments are effective in the face of mind control, which is a bit of a gamble. A strong enough will is able to overcome the Imperius Curse, but Peter isn't a strong-willed person, and gambling on his self-preservation instinct to work wonders seems like a good way to lose a friend.

  Second, it seems as though a secret cannot be divulged under the Imperius Curse anyway, as Pottermore goes on to say:

  In spite of the fact that the secret can only be given up voluntarily, many have been subjected to the Imperius and Cruciatus Curses in an effort to make them share their information.

  ^{Pottermore Secret Keeper}

  So no benefit here either.

• Accidentally. We might imagine a situation where Peter goes down to a pub, gets blitzed out of his skull, and accidentally blabs the Potters' secret to the entire establishment.

  Leaving aside the fact that we'd also expect Peter's natural cowardice to keep him away from public places, the Potters almost certainly wouldn't have chosen him in the first place if they'd felt this was a likely possibility. An Unbreakable Vow might provide some benefit in this situation, but it's a pretty slim benefit in the face of the trust that they already have in him to not be a moron.

• Voluntarily. This is the only place an Unbrekable Vow provides any material benefit: Peter would have to weigh his loyalty to Voldemort's cause against his own instinct for self-preservation. But the benefit here assumes that Peter has loyalties to Voldemort. We know this, but James and Lily didn't; again, if they'd known they wouldn't have made him their Secret Keeper in the first place. As far as they knew, he was totally loyal to them and their cause, and would have absolutely no reason to willingly divulge their secret to anyone nefarious.

  As with the previous case, whatever benefit an Unbreakable Vow provides is negligible compared to the faith they alreayd have in him.

Answer 3

They didn't think they had to.

Peter was one of James's best friends when he was at Hogwarts, and they had a false sense of security with him as Secret-Keeper. The Fidelius Charm can work better than an Unbreakable Vow if the Secret-Keeper is loyal. Besides, if Peter was bound not to tell anyone where they were, he could show Voldemort. Or, even more likely, Voldemort could just find them by himself.

On the other hand, if the Potters used the Fidelius Charm and an Unbreakable Vow, they would be virtually unfindable. But they trusted Wormtail with their lives, and besides, he was only the backup Secret-Keeper. Another reason might be that if Wormtail was forced to reveal the location, that would mean the deaths of James, Lily, Harry, and Wormtail, instead of just the first three.

Answer 4

I agree with the other answers here, more or less, but would like to bring in another angle.

The Unbreakable Vow is a dark spell.

Lifting the quote from A. Darwin's answer:

“An Unbreakable Vow?” said Ron, looking stunned. “Nah, he can’t have. . . . Are you sure?”

“Yes, I’m sure,” said Harry. “Why, what does it mean?”

“Well, you can’t break an Unbreakable Vow. . . .”

“I’d worked that much out for myself, funnily enough. What happens if you break it, then?” “You die,” said Ron simply.

Sounds like the kind of magic the Potters would not touch, on general principles, let alone inflict on someone they consider their trusted friend.

What do "good" wizards think about it? Let's hear Ron tell about the time his brothers tried a prank on him using the Vow:

"Fred and George tried to get me to make one when I was about five. I nearly did too, I was holding hands with Fred and everything when Dad found us. He went mental, only time I've ever seen Dad as angry as Mum. Fred reckons his left buttock has never been the same since."

Bellatrix and Narcissa had no qualms using it on Snape, but I can't picture either James or Lilly using a potentially lethal spell like that, casually, "just" to ensure their personal safety.

Answer 5

Peter wouldn't have agreed

The Unbreakable Vow requires agreement to the vow, it can't be imposed, and Peter, given his cowardly nature, wouldn't have accepted such an arrangement.

Keep in mind that Peter's cowardly nature is why they decided he was a good Secret Keeper, as Voldemort would've never suspected it.

I'm not sure, but I seem to recall the Peter even resented being made Secret Keeper, not wanting to shoulder such a responsibility, so it is doubtful he would've gone for an Unbreakable Vow.

And, in any case, as has been mentioned by others, it goes against character for the Potters to threaten one of their friends with possible death for their safety's sake.