I wanted to re-post this because it was one of the most awesome posts I recall reading on the Lords of Lemuria board, and failing to include it in this area would be deserving of the Spell of "Forlorn Encystment."  In this thread, Korvargr wrote:

What is the function of Vancian spells in the fiction, the Dying Earth novels? 

The names are rather "baroque" like "Excellent Prismatic Spray". But what does it do? 

What such a Vancian spell acutally does in the story is to provide a kind of "wildcard" to put into ANYTHING that saves the magician's day! 

So having "memorized" 4 spells of rather strange and quite unspecific names (compared to more functional names like "Fireball" or "Finger of Death") is the equivalent of having 4 "magical Hero-Points" to "edit the scene" using a kind of magical "trapping" to describe the outrageous effects, by which the magician works his way out ouf trouble. 

If you put aside the actual misnamed thing that is D&D-like fire-and-forget-magic, and take a look at Vance's stories, then you'll see that those stories actually do NOT really use a kind of fixed descpritive spell system, but in fact only "talk about it", while actually leaving the reader for the most part in the unknown about what the hell this strangely named spell might do. 

When it is time, that the hero is in dire straits, unable to save himself by physical prowess or glib tongue or sharp thinking, those spells give him a kind of "flashback preparation"-moment (like in the TV-series Leverage). 

Although the reader (or player) does not know, what magical effect might be needed in an adventure, the character SEEMS to know it in advance (though actually he doesn't, because even the author or the player couldn't see into the future). 

So, when the spell is used, it takes effect in a way, that promotes the story, that saves or benefits the magician protagonist, that let's him show off how AWESOME he is to think up the necessity of such a strange spell in advance! 

The function of Vancian magic is to promote the AWESOMENESS of magician characters. - This is nearly the opposite of a "fixed formulaic spell, decide in advance, fire&forget"-spell-system! 

So, what is needed in BoL to correctly represent Vancian magic and Vancian mages? - Nothing new! - When a magician character declares, that he would use a magic spell, he has to NAME it - just then, not beforehand, no deciding in advance! Then he performs this spell, employing the necessary amount of Arcane Might and other requirements of the spell, and then this spell is considered "gone". 

Gone in the FICTION of the played story. Not in any kind of rules-mechanic kind of sense. 

The Arcane Might expended on the spell comes back after some time. What does the magician do in this time? - Well, obviously he "relearns", he "memorizes" this spell or another one in the off-time while waiting for his Arcane Might to regenerate. 

As a matter of fact: In no BoL game I've ran any mage used the same spell twice. Ever. - Even if similar effects were desired, it always was a remarkably different spell. 

So no typical spell-point-system feeling like "I cast fireball", "I cast fireball again", "I cast another fireball, because I have enough points to do that". 

Also no ignoring of useful, but not so generally powerful (= killing) spells like in D&D, where many, many spells nearly never ever were memorized, because some method of magical killing is universally more useful, than a Spider Climb or a Mend now and then. 

In BoL the magician PC may declare: "I've foreseen the need to ascend this tremendous, unclimbable heights in my Lotos enduced vision dreams last night. Therefore I've memorized 'The wondrous Climb of the nifty Spider', a powerful spell, that allows the recipient to climb this sheer wall of despair. Any volunteers?" - And then this First Magnitude spell is handled by the normal BoL rules. 

BoL actually captures the FEELING of the magic as presented in different flavours in different author's Sword&Sorcery novels quite well without any rules changes needed. The feeling is all in the description, all in the story. So reading (and re-reading) of novels by a certain author helps to maintain the correct flavour. 

Vancian magic is the magic of pure awesomeness performed by highly competent, smart and strong willed characters. - I suggest to measure any BoL house rules for Vancian magic against this yardstick. (In my opinion, the D&D-like spell system delivers quite the opposite feeling by having to make decisions as a PLAYER in advance, instead on relying on the awesomeness and experience of the CHARACTER to implicitly decide, what spell might be needed. Therefore the "Vancian magic" in D&D falls several miles short from any of the Dying Earth stories' magic.) 

So much for my "Most astonishingly lengthy and wordy Display of Thoughts" spell.