The first-years conspiracy

[kgpopp]

No: HPFGUIDX 142109

> Even if the Felix had worn off by the time Slughorn gave Harry the 
> memory, by this point, Harry had wheedled him and gotten him 
drunk.  
> It's still due to the Felix that Harry receives the memory at all. 
I 
> do happen to think it's the right memory, though I'm not sure how 
> Dumbledore knew that memory was SO IMPORTANT.)  It is a good point
> that maybe something ELSE that happened in the hut could have gone 
> better if Harry had measured more carefully.  Something relating 
to 
>Hagrid, maybe?
> 
> Allie
>

KP:  I was thinking about your question as to how Dumbledore knew 
the memory was important 
 and 
 

When Dumbledore realized that Tom Riddle was a threat, I think he 
decided to start trying to get all the information he could about 
Tom/Voldemort because knowledge is power.   Therefore, Dumbledore 
would have tried to get information from anyone that knew Tom before 
he emerged as Voldemort.  Naturally Dumbledore knew that Tom was 
part of Slughorn's group while in school and would have tried to 
talk to Slughorn.

Now, Slughorn knew that it saw a big taboo for him to talk with a 
student about horcruxes.  He also knows Tom is Voldemort.  So when 
Dumbledore tried getting background on Tom; Slughorn was 
ashamed/scared and tried to hide his memory from Dumbledore.   I 
think the fact that Slughorn tried to hide the memory is why 
Dumbledore thought it was important.    

Now it is not clear if Dumbledore realized the importance of the 
memory when he 1st talked to Slughorn or if overtime he realized the 
potential.    But, at the point in time when Dumbledore is sharing 
Tom's history with Harry; it clear that Slughorn is hiding something 
big.   I mean by then Dumbledore already has a good inkling (if not 
certain) that Tom Riddle/Voldemort had created a Horcrux, because  
the AK spell didn't kill him.  Dumbledore also knows from 
the "tampered with memory" that Slughorn talked with Tom about 
horcruxes.    Now it stands to reason that if Slughorn tried to hide 
the memory from Dumbledore then there is more to the story.  I don't 
think Dumbledore knew that they'd learn the number of horcruxes but 

 I think he knew it was important to Tom's past.