Can there be nuances or uncertainties in the Unbreakable Vow?

Snape made an Unbreakable Vow to watch over Draco, protect Draco, and to kill Dumbledore in his place if he couldn't do so. However, it doesn't give an exact date to do the killing.

Also, what if Snape failed but attempted to do what was said in the Unbreakable Vow? For example, if Dumbledore, luckily, wasn't disarmed and incapacitated Draco, and beat the Death Eaters and Snape alongside Harry? Would Snape die?

  • 3
    I think the vow was to take up Draco's mission in his place. And that vow is fulfilled if Snape takes up the mission...and fails.
    – tbrookside
    Oct 31, 2021 at 0:36
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    This is pure speculation, so I'm writing it as a comment: In my opinion, an Unbreakable Vow would kill you (a) at the time limit (if specified) (b) the instant you lost the intent to follow through on the vow (if time limit is unspecified)
    – Righter
    Nov 3, 2021 at 5:29

1 Answer 1


Half-Blood Prince doesn't say exactly when a death from a broken Unbreakable Vow will occur:

"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.

Harry Potter and the Half-Blood Prince - Chapter 16, A Very Frosty Christmas - Pages 325-326 - Scholastic Books

So, there's nothing written in stone (i.e. canon!) about when death from a broken Unbreakable Vow will occur. However, we can look at other spells and hexes that are capable of causing death. Avada Kedavra causes immediate death. Sectumsempra acts immediately upon being cast. The Fidelius Charm also acts immediately (and while Fidelius doesn't in itself cause death, its Secret Keepers are in constant danger of death once the charm is cast). Moody demonstrated in Goblet of Fire that both Imperius and the Cruciatus Curse act immediately upon being cast.

Yet, we also see slow-acting magic in canon. The most obvious example is Dumbledore's hand, which was fatefully injured by the magic protecting Tom Riddle's ring when Dumbledore tried to put it on. Snape spent almost a full year keeping Dumbledore alive; however, the curse would have eventually killed him. This is one example.

I believe, based on consideration of a variety of spells, charms, and hexes, that death from breaking an Unbreakable Vow would be instantaneous.

  • For the certain value of "breaking", I guess. I believe there is some wiggle room there, from the point you decide to break it to breaking it. There is another spell which might be applicable: silver arm for Peter Pettigrew. As long as he served Voldemort, the arm served him. The instant he wavered even slightly in his devotion, it strangled him.
    – jo1storm
    Nov 3, 2021 at 9:08
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    @jo1storm - I see what you mean and Pettigrew's silver hand is a great example of magic that can both kill and operate on a time delay. :) Nov 30, 2021 at 17:16

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