On the trivial and the profound.

[pippin_999]

No: HPFGUIDX 165577

> >Eggplant:
> > That is the mother load! If you can find a RATIONAL reason a good
> > Snape would make that vow you will instantly turn me from being a
> > Snape hater into a Snape lover.
> 
> Neri:
> Agreed. However, the vow doesn't seem much more rational from the POV
> of ESE!Snape. True, ESE!Snape wouldn't mind killing Dumbledore, but as
> he says himself he's going against the Dark Lord's orders in making
> the vow. 

Pippin:
Not quite. Voldemort hasn't ordered Snape not to kill Dumbledore, he's
ordered him to let Draco try first. It's only in the unlikely event that
Draco succeeds, according to Snape, that Voldemort will be able to
let Snape continue at Hogwarts as a spy. Once Draco's failure is
inevitable, there's nothing in ESE!Snape's way. 

Of course it all depends on what Eggplant means by rational. If
'rational' means 'rational self-interest' then neither ESE!Snape nor
DDM!Snape need apply, because both are serving causes for
which they would sacrifice their lives.


Neri:
And moreover, he also puts himself in a big risk, because if
> Draco tries killing Dumbledore on his own and fails or gets hurt
> before Snape can reach them, then Snape is dead. So it looks like
> Snape has reasons of his own to make the vow, which by definition
> means OFH. 

Pippin:
Huh? If Snape doesn't take the vow, why should Draco's failure
mean his death? Or are you referring to the first two portions? They
require Snape to watch over Draco, and protect him *to the best of
his ability. *  

Neri:
> 
> While I frequently sound like I'm joking when promoting ACID POPS, I
> must say that I don't know of any other theory that is even close to
> explaining why did Snape make the vow. And as a nice bonus ACID POPS
> also explains another unsolved mystery: what did Draco suddenly have
> against Snape in HBP, after liking him so much for five books.  
> 
> 
Pippin:
Oh, LOLLIPOPS works just as well. Lollipops!Snape sees himself
in Narcissa. Her loyalty to the Dark Lord has endangered her 
dearest blood, and Snape pities her. She's begging
for his help to save Draco, as once, perhaps, Snape begged
Dumbledore's help to save Lily. 

But unlike Dumbledore, who trusted Snape, Narcissa does not,
and asks for the vow. What can Snape do? If he refuses, that's as
good as saying she's right not to trust him. Who knows what
she'll do then?

Also, let's say Snape knows about the plan and not about the
cabinets, but unlike Dumbledore, he doesn't think that smuggling
DE's into Hogwarts is impossible. And then Bella and Narcissa,
show up on his doorstep. 

It might be his big chance to find out what Draco is really up
to without tipping off Voldemort or putting Draco at risk.

Then we must distinguish between the vow and the
magic that binds it. DDM!Snape is not a man of his word. He has
foresworn his vows to Voldemort, and I don't suppose it
would bother him to make a false promise to Narcissa. 
He can give his word to carry out a task with no intention of
doing so, and the vow will not strike him down. It will only
get him if he fails to perform the task under the set conditions.

If Dumbledore is right and it's impossible for DE's to enter
the castle, then the set conditions will never arise because
Draco will never get close enough to Dumbledore to make
his failure inevitable. You have to try before you can fail.

On the other hand if Dumbledore is wrong, and there is a
viable plan to get the DE's inside, that is information that
DDM!Snape would certainly risk dying for.

If he refuses the third portion of the vow, then he's on his
knees with his wand hand bound, and an armed killer 
standing over him. Bella shouldn't be underestimated;
she was the last DE standing at the Ministry. Even if she
doesn't kill him outright, he's in an impossible position;
what if she asks him to swear, right then, that he's
been faithful to the Dark Lord since his return?


Pippin
noticing that if Snape sent the Order to the Ministry and
didn't believe that Harry was there, he did more than 
leave his fellow DE's in danger. He set them up.