Some logic on Snape/Dumbledore

[snipsnapsnurr]

No: HPFGUIDX 134084

Here is something that occurred to me. If you believe as some 
people do (not me, but that isn't important) that Dumbledore 
was asking Snape not to kill him when he said "Severus. . . 
please", I think you must also believe that Dumbledore did not 
know about the part of the unbreakable vow that required Snape 
to finish Draco's task if Draco could not.

Let me explain. At the point when Snape arrived at the tower, 
Dumbledore knew for certain what Draco's task was. He may have 
known before that, but we cannot say for sure. If Dumbledore 
did know that Snape had vowed to complete Draco's mission, he 
would realize that Snape would die if he didn't kill Dumbledore. 
I believe that Dumbledore would sacrifice his own life for 
someone else, but I do not believe that he would ever, under any circumstances ask someone else to sacrifice his life to save Dumbledore. If he knew that detail of Snape's vow, that is what 
he would have been asking Snape to do.

I think it is likely that Dumbledore knew about that part of the 
vow, and I will explain that in another post. But either way it 
is something to keep in mind when trying to work it out. I hope 
I was clear. It's kind of late here.

snipsnapsnurr