The Origin and Use of Magic in OD&D part 1

If you were thinking that this post is going to be something claiming to be a definitive answer, sorry that is not what this is about and each post will only deal with a little bit of the issue. The will likely be a lengthy series of posts.

OD&D does not have any explicit statement about the origin of magic and IHMO that is a good thing, an excellent thing even. It leaves it entirely up to the DM to decide for himself the origin of magic within his campaign. Now why do I think that is a good thing?

One of the things that some complain about is the issue of the "clerical" magic of the Cleric and the "magical" magic of the Magic-User. Now in OD&D RAW they function essentially identically. Now for Magic-Users spells are held through memorization (Vancian Magic) and for Clerics spells they get them from their diety. That is the common belief. But what does Men & Magic, Volume 1 of OD&D say?

Spells & Levels: The number above each column is the spell level (complexity, a somewhat subjective determination on the part of your authors). The number in each column opposite each applicable character indicates the number of spells of each level that can be used (remembered during any single adventure) by that character. Spells are listed and explained later. A spell used once may not be reused in the same day.

Read this several times and think about it. What do you think it means? There are a number of points to think about, here are a few things (not intended to be a comprehensive list)

1. The number in each column opposite each applicable character indicates the number of spells of each level that can be used (remembered during any single adventure) by that character. A spell used once may not be reused in the same day.
1. A. "during a single adventure," what does that mean? If I play through two weeks of game time, including travel to a dungeon and then three forays into the dungeon on three different game days is that a single adventure and so a 1st level Magic-User would get one Sleep Spell for the whole two weeks? I don't run it that way, I run it per 24 hour period (or whatever the full day is on a given world). How do you run it?