1 or 2e. Can a caster "Forget a spell"?

[garhkal]

Lets say finenous the magister has 2 magic missiles, 1 sleep, 1 det magic, 2 blurs, 1 cont darkness, 1 fireball and 1 dispel magic in his memory... During the day he casts none, but realizes the group may instead of his blurs, need a few knocks the following day.
Can he simply forget his two blur spells? Or must he cast them to 'clean then out of his memory, so he can then memorize two knocks"?
If he does have to cast them, can he just start, then stop, causing it to fizzle much like if he got hit? if so, are any material components the spell calls for, consumed?

Additionally, i remember a rule somewhere (not sure if 1e or 2e) where when a caster is knocked out (or goes negatives), he loses all spells he had in his mind.. Anyone know where that's from?

[JadedDM]

I allow spellcasters to forget spells. But forgetting is the same as casting, in the sense that you cannot refill that slot until you've rested.

Additionally, i remember a rule somewhere (not sure if 1e or 2e) where when a caster is knocked out (or goes negatives), he loses all spells he had in his mind.. Anyone know where that's from?

Hovering on Death's Door rule, in the 2E DMG.

[garhkal]

Thanks.. Knew it was somewhere.

[Halaster-Blackcloak]

I'd say he has to cast them to "clear" them. He can't just "forget" them. Remember, spell energy is stored in his mind. That energy has to be released before he can re-energize, so to speak. If he dies and is resurrected or raised, all his memorized spells are wiped out. If using death's door rules, as JadedDM pointed out, the spells are likewise wiped out if he goes into the negative.