Snape and the DADA curse.

[William Bernard]

No: HPFGUIDX 148875

  Tonks_op said:

  >> DD needs Slughorn to be at Hogwarts so that he can get the   
  memory out of him. This is more important than Snape not getting 
  the DADA position.  Since in order to get Slughorn DD has to offer 
  him the Potions Masters Position, DD then naturally has to give 
  Snape the DADA position.

  Before he went to find Slughorn DD knew he would probably get him 
  to say yes. DD told Snape that he could have the DADA position 
  before he went to Slughorn.  In this way the DADA curse already 
  had a chance to start and this is part of what caused Snape to get 
  into the position of having to take the unbreakable vow. <<

  Bill Here:
   There might be a simpler explanation for events. Suppose that DD expected Slughorn to stay for only 1 year. He moved SS to DADA and had Slughorn teach potions. At the end of the year, Snape would go back to teaching potions and a new DADA teacher would be found, or at least looked for.
  This takes into account the jinx that DD suspects is there, but solves his problem for a year. Things just didn't work out in the fashion expected.
  Bill