On the trivial and the profound.

[Neri]

No: HPFGUIDX 165556

>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. 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. 

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.  


> Eggplant:
> Voldemort's plan was to trick Harry to go to the ministry, but when
> Snape showed up Harry was already caught by Umbrage so Snape figured
> the plan had failed, it never occurred to him that Harry would manage
> to escape and make it all the way to the ministry. With the plan
> canceled anyway it couldn't hurt to tell the Order of the Phoenix
> what Harry said, in fact he had to if he wanted to remain a spy for
> Voldemort. Ron, Hermione, Neville, Luna and about a dozen other people
> heard Harry talk to Snape about Padfoot, and sooner or later the Order
> would hear about it and wonder why Snape didn't tell them immediately.
> 

Neri:
A good point. However, Snape actually contacted the Order *twice* that
night (or at least this is what Dumbledore believed). The first time
was indeed after leaving Umbridge's office, when he checked on Sirius
in 12GP. This call alone might be enough for ESE!Snape to prevent the
Order from suspecting him. However, Snape warned the Order again
several hours later, when Harry did not return from the forest, and
this second call is more difficult to explain using the ESE theory.
There's also the question of why doesn't ESE!Snape also warn
Voldemort, immediately after leaving Umbridge's office, that the
operation must be canceled, and instead lets Lucius and eleven other
DEs risk their necks in the Ministry for no reason. IMO Snape's
strange behavior here strongly suggests that he has his own agenda,
and that he's torn between contradicting objectives.

Neri