I'm not asking about the rules or concepts of spell preparation, as they are well described and reasoned, but I'm wondering why it's even necessary, from a logical (well, however logical you can be in a fantasy RPG) POV.

Why do spells need to be prepared? Why can a fighter or a rogue use insta-abilities whenever he wishes, but a mage/cleric/palading can not?

I always found the concept of preparing spells very very confusing and very hard to explain to new players. It's just not intuitive.

What I can understand however is, that you can only cast a certain amount of spells during a day. That's okay, as I can imagine casting to be very, very exhaustive (mentally, obviously).

Why not just say: "You can cast 1 spell per day" and be done with it? Which one it is doesn't really matter in the end, because you are ALREADY limited by the amount you can cast.

Furthermore; wouldn't the Mana concept be even easier? Having some points that regenerate while resting, and every spell having a different amount of needed points?

Why limit it twice?

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    \$\begingroup\$ Related: rpg.stackexchange.com/questions/12310/… \$\endgroup\$ – Simon Gill Jan 15 '13 at 15:45
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    \$\begingroup\$ Don't overlook @SimonGill's link there—It's not quite a duplicate question, but its answers get into the origins of the D&D spellcasting paradigm, including the fictional reasons for spell preparation. (Basically, it works that way because that's how they chose to make it work—it has nothing to do with "most logical", because it's copying how magic works in a particular series of novels.) \$\endgroup\$ – SevenSidedDie Jan 15 '13 at 16:32

Here's a link to an article which answers your question pretty accurately.

Q: Where such a system came from?

A: Jack Vance. The system first appears in a book "Dying Earth".

Q: Why Vancian magic for DND?

A: Because Gary Gygax loved it.

It is not necessary - it is just a design choice made early on and not changed thereafter.

As for Gary Gygax, see this.

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    \$\begingroup\$ This answer risks becoming meaningless if that link succumbs to link rot. Please consider giving an overview or summary of its explanation/argument/line of reasoning/relevant statements. \$\endgroup\$ – SevenSidedDie Jan 15 '13 at 16:35

Up to 3.5 and Pathfinder, Dungeons and Dragons allows you to use mundane abilities whenever you like.

Magic is limited, both in being hard to channel but by time. It takes minutes to cast even the simplest spell. Spell preparation is similar to winding the elastic in a toy plane. You can hold the propeller for a while until you decide to let it go. In a similar fashion, the act of casting is letting the spell's energy loose in a predetermined fashion.

Sorcerers are a strange part of the system. They have the energy of the spell set and ready to go at a moments notice. Tacroy has pointed out that sorcerers are like Rainman - they can give you instant answers in a limited field where wizards are more like a usual mathematician. A wizard is going to have to take time to work out the same answer, but he can work in many different fields.

Psionics in D&D runs on the power point system and Ernir has produced A Translation of Vancian Spellcasting to Psionic Mechanics that makes for an arcane flavoured spell point system.

One of the reasons for the limit is to encourage people to consider what could happen over the coming day and make choices of what spells can be used. It's almost a minigame of its own.

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    \$\begingroup\$ @Pulsehead It's like the difference between someone with savant syndrome and a mathematician. The savant can give you answers instantly, but only in a limited field; the mathematician can give you answers in any field, but it takes time to research them. \$\endgroup\$ – Tacroy Jan 15 '13 at 16:49

As others explained, the in story reason is that you are basically doing the hard part of the casting up front so that you can finish just the last little bit very quickly when the time comes.

It also has a balance perspective. They only want to give you so many options at a time. Now, its true other systems don't use spell preparation, but those also either give mages many fewer spells available (this includes Sorcerors in D&D who don't need to prepare, but know on average a lot fewer spells than a wizard of the same level) or else they make mages extremely versatile and powerful on purpose (such as Mage: The Ascension where mages are meant to dwarf any non-supernatural).

But as for it making sense and being able to explain it, there are other real world and fictional examples. Think about the light shows at some concerts. Technicians can do a lot of it with a push of a button...because the stage crew spent hours ahead of time preparing that particular location and many more hours before that planning and figuring out how to do that preparation.

In fiction, think about Batman. Again its not a perfect example, but he frequently custom builds gadgets and carries a very specific set of preparations on him. A very common trope in the Batman mythos is that he will lose horribly to some villain, go off and prepare specifically for that one fight and then come back and win mastefully because he was ready. In a lot of ways, a D&D wizard is like Batman while a D&D sorceror is like Black Lightning (or most other superheroes.) Batman/a wizard has a huge arsenal of tricks and can get more tricks quickly and easily, but he needs to get them ready ahead of time, Black Lightning/a sorceror has a more limited pallette, but they do them just about any time they aren't exhausted without doing much to really get ready.

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    \$\begingroup\$ Batman is a great example - because D&D 3.5 wizards are Batman. Best when they have options and time to prepare. \$\endgroup\$ – Simon Gill Jan 15 '13 at 17:41

It's not "necessary." Many other games exist where magic doesn't work that way, including various magic systems within D&D.

D&D magic was created to specifically mimic Vancian casting (magic the way it works in the novels of Jack Vance) and so that's why it works that way.

This question is largely meaningless because it doesn't "have to work that way," it's just an early D&D design decision that people have stuck with because it works pretty well in a game. There are infinite other ways to do it as well.


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