R S. Eider's Hilchot Hanukkah
P. 16 Paragraph 4 "Use for Mitzvah"
See Aruch haShulchan [AhS] O"Ch 673
Especially s'eifim 7,8.
The Issue is Given:
We may NOT use Ner Hanukkah for our personal use. The remaining question is:
May one use Ner Hanukkah for Tashmish Mitzvah ?
The Ittur says: YES! this is not Bizayyon, rather it is Kavod and is exempt from any prohibition
Some say this heter is only ad hoc, but does not allow one to learn "derech qavu'a"
Most [Rov] Posqim say: No use is Good use! - because there is no Heker that it's for the sake of Hanukkah
And so is "haminhag happashut"
Methodology Questions to Ponder:
• Are Both Reasons necessary?
• Is each reason sufficient on its own right?
• Is it enough to Pasqen by Rov Posqim alone?
• Is it enough to follow the Minhag happashut even where there is no definite rov?
• How about a Minhag against a rov? Would Minhag trump Acharei Rabbim l'hatot? [as per AhS]
•. May one rely upon this Ittur?
• Is there any evidence from the original sources one way or the other?
• Would "hints" or philology from the original source matter one way or the other?