How does the Unbreakable Vow reconcile contradictions/paradoxes?

Question

The Unbreakable Vow seems ripe for scenarios where it could be contradicted by circumstances that would be common in the wizarding world. For instance:

• Is it possible to swear an Unbreakable Vow with immortal beings such as Poltergeists and Dementors?
• What if you swear to stay alive and you break the Unbreakable Vow by being murdered?
• What if you swear to die?
• What if you swear to do something impossible, such as revive the dead?

Is there any indication in any of the canon works (books, movies, JK Rowling's interviews) that suggests how such a scenario would be resolved? Would the Vow merely fail to become valid, would it resolve immediately in death, or something else entirely?

If there is nothing about this particular magic spell, is there any indication of how magic in the Harry Potter universe resolves paradoxical magic in general?

Answer 1

I think emotion and intent are important factors with the magic in the Harry Potter universe. We know they're definitely important for the Unforgivable Curses, from what Bellatrix Lestrange says in Order of the Phoenix:

Never used an Unforgivable Curse before, have you, boy? You need to mean them Potter! You need to really want to cause pain - to enjoy it - righteous anger won't hurt me for long

Splinching when Apparating could easily be related to this - Ron splinches when he's panicked and under pressure trying to escape the Ministry in Deathly Hallows - or to the skill part of magic, which we know is a factor in every spell and is why not everyone is an Animagus or an Occlumens - and why basic magic is something you have to study for seven years at Hogwarts!

If we take emotion, intent, and skill as factors in every spell, then we can extrapolate and say if you were making an Unbreakable Vow like, 'I will revive the dead', both you and the person you were promising it to would have to have a clear idea of what that promise entailed. Are you promising to find the Resurrection Stone? Are you promising to make Inferi? Both of those would be possible to do.

Canon doesn't suggest anything about time limits on Unbreakable Vows - if no time frame was set when you made the Vow, you might be able to make a promise like that and live your whole life, intending to do it at some point. Given you make the promise to another person, though, it's likely that if they don't believe you are holding up your end, the spell begins to take hold.

As we haven't seen spells that involve other people before, it's likely that the second person is needed for more than dramatic tension; it's them you are actually making the promise to, underlined by the fact you need a third person to perform and bind the spell. We could make a logical jump and say the emotions of the person you've made your promise to are the trigger of an Unbreakable Vow.

As an example, if I made a Vow to you that I would never be angry with you, I would live if you didn't perceive that I'd broken my Vow. I could be mad as hell at you and live as long as you didn't know. If you saw that I was angry - if I started yelling and kicking nearby nogtails - I would die. (As well I should. Those poor nogtails.)

I think the Vow we see in Half-Blood Prince backs this view up. Narcissa's words are chosen very pointedly, formally, and carefully when she asks Snape:

will you, to the best of your ability, protect [Draco] from harm?

If we take that line as written in stone, then if Draco stubs his toe when he gets out of bed in the morning (this is assuming Snape's not around, all you naughty fan fic writers), then Snape's off the hook. Draco came to 'harm'; it wasn't within Snape's ability to 'protect him'.

If Snape were to see Draco about to stub his toe and the Vow was word for word literal - boom, dead.

I think we have to assume, then, that it's Narcissa's feelings that matter here more than anything; if she perceives Draco has been harmed and feels it was within Snape's ability to protect him, then Snape's a goner. (Whether a stubbed toe would cut it is a question for another day. She's a pretty protective mother.)

As for what would happen if people tried to make a Vow they weren't completely in agreement on, I don't think it would work.

There's no canon to back this up but we have seen other spells being cast and fail or being cast and only doing a weak version of what they were intended to do, like Harry casting the Cruciatus Curse at Bellatrix Lestrange, and not having it hurt her full-force.

I think we can take that as a mark of how magic works in general, and take it to mean if both parties didn't have a completely clear - and matching - understanding of the promise, the promise wouldn't get made. As the spell is quite a big flashy one with a 'brilliant flame' wrapping around the hands of the people making it with every promise, we can assume there wouldn't be any fire or it would fizzle out, the same way beginners make 'wisps' and indistinct silver shapes before they make a full Patronus. It would be clear that the Vow hadn't worked properly.

Answer 2

Rather than debating the nature of unbreakable vows (which seem ill-defined at best), it might simply be easier to use logic to identify what would happen in the circumstances you've mentioned;

Is it possible to swear an Unbreakable Vow with immortal beings such as Poltergeists and Dementors?

No. Dementors don't appear to be able to speak and poltergeists are unable to hold hands, both of which seem to be key features of the spell.

What if you swear to stay alive and you break the Unbreakable Vow by being murdered?

Then you're dead and the status of the vow is moot.

What if you swear to die?

Unless you put a timescale on the spell (e.g. I swear to die within 1 day) then the answer is "probably nothing". The only way to break the spell would be to live forever, a logical contradiction.

What if you swear to do something impossible, such as revive the dead?

Then you'll die.

Answer 3

Contradiction

If you eg. swore to protect someone as well as kill them, you'd die in any case - but if you didn't say when you could probably still live a while, since none of the vows would have taken effect.
Also, you might be able to find a flaw in the paradox - for example protecting that person from torture by killing him (if there was no other way to protect him).

Poltergeist

It seems like the magic of the binder (or however the 3rd person is called) has to be able to kill the bindee/victim if the promise is broken (in canon it is implied the binder supplies the magic, the 'bound-to' the content of the vow, and the bindee the agreement; in the HPMOR fanfic the vow doesn't kill but alter your thoughts/behaviors directly - it's truly unbreakable - which means vowing a paradox would probably drive you insane, which could occur to poltergeists etc.), so it would work only if the binder somehow has the power to kill the bindee (maybe the binder would die if he tried to bind such a vow?).

Swear to stay alive

You die as soon you cease staying alive - which you would have done in any case, vow or not.
edit: you might be half-dead due to horcruxes or unicorn blood, in which case the vow might try to kill you off completely, depending on whether that spell-technically counts as alive - no idea whether it would succeed against the methods mentioned above, though.

Swear to die

This one is interesting. Does the vow trigger when it becomes impossible to attain the goal? This would necessarily be a long term acausal effect, which (probably) not even magic could do. It might trigger if one thought the goal was impossible to attain, but that would make the victim vulnerable to a confundus or maybe even nightmares, going against the intention of the vow. Assuming causal objectivity (it's independent of anyones thoughts once cast), this vow should either kill you immediately as soon as you could have killed yourself (if immediately it would go against the general intent of the vow - giving a strong incentive to achieve the goal - for which dying wouldn't help in most cases) or just prevent you from attaining permanent immortality, depending on how it works with delaying (if I swear to marry X, but delay the marriage by a day due to bad weather, will I die? I'd assume no, so it should generalize to 'disrupting immortality', but this isn't really certain from canon).

Revive the dead

When Snape took his unbreakable vow, it didn't just state 'protect Draco' but also modifiers: 'to the best of your ability' (or something like that) - this implies that either the vow would have killed him as soon as Draco was 'unprotected' (this might not even necessitate actual harm!), or only obvious non-protection would have resulted in Snapes death (like with 'swear to die', it depends on how 'trigger happy' the spell is) - so either you would die since you didn't revive the dead right now (or at least start casting the (nonexistent) revival spell), or it would only kill you if it was obvious the spell failed.
In general spells in HP behave anthropomorphic - eg. implementing high-level concepts like 'happiness'(expecto patronum) or 'hate'(avada kedavra) - so we have to assume that the detailed mechanics of the spell would depend on the intent of the inventor of the spell, (and/)or one/all/the average of the 'executers' (though this influence would not be arbitrary - you could never revive someone with a love-cast avada kedavra or turn a marble blue with a wingardium leviosa while thinking blue thoughts). Doing your best should most likely prevent vows from triggering (unless it's a 'fail defined' vow like 'keep X alive' or 'don't touch the ground'), but taking a more opportunistic approach ('I'll revive the dead when someone teaches me the spell') might or might not, depending on intent.