So, to me, what defines a wizard is that its spells are from books. There's a lot of different ways to be a "book," from a literal tome to tattoos to runestones to papyrus scrolls, but what all wizards share is that their magic comes from studying and applying magical knowledge gained from some form of language or formula. Non-literate societies cannot produce wizards, because wizards must have some form of "language," because that is how they access their spells.
Because of this, wizard spells are ritualistic, regimented, and have a grammar, order, and pattern to them. When a wizard casts a Fireball, it is because they have spoken its true name and given it shape with the structure of their sentence. When a wizard casts Invisibility it is because they apply a formula to their subject which dispels the elements of their subject that can be seen. Wizards are book-bound. They are educated spellcasters.
I think this comes into play mostly with the idea of "preparing" spells. Wizards prepare their magic in advance. They study. They anticipate. Whether they use at-wills, dailies, or spell points, or whatever, their spells are prepared from their books in advance. They essentially "equip" themselves with a spell list every morning.
This gives them remarkable versatility and adaptability. They can know a wonderful spell for a specific situation. They have the precise tool to accomplish a goal, if they know about the goal far enough in advance. Whatever magic system a wizard is under, I hope they have this element.
What defines a sorcerer for me is that its spells are from itself. It's a mutant. There's a lot of different ways magic could be inside of you -- questionable parentage, bizarre ritual, drank a water elemental as a kid, spent a little too much time with the fey...but whatever mutated the sorcerer, their spells are things that arise from within them.
Because of this, a sorcerer casts its spells easily. It doesn't need the elaborate rituals and grammar of the wizard. Casting magic is reflex for a sorcerer, in-born and automatic. Casting burning hands is as easy as using a fork, and learning fireball might be like learning to use chopsticks. Sorcerers are intimate with magic. A wizard's spell might be highly dictated calligraphy, a Sorcerer's spell is graffiti. It's personal.
I think this comes into play in the idea of having a "locked" spell list. A sorcerer who learns Fireball isn't speaking some arcane grammar, they're just wiggling their fingers and shouting some nonsense and there it is! But because they are their own spellbook, they can't change these spells. Changing that fireball to a lightning bolt would be as impossible as willing yourself to have an extra finger, or growing a second head, or squinting to change your eye color. But since magic is easy for them, they can do it repeatedly. They don't spend up their arcane energies forming careful magical poetry, they freestyle, creating magic out of their own personal reserve, and so they produce much more quantity. They can't grow an extra eye, but they can blink the eyes they have all they want.
I think to reflect that, you might want to give sorcerers an option, at first level, of choosing a "bloodline" that locks them into certain spells as they advance, and maybe giving them more at-will and recharging magic. A sorcerer might not use any daily spells. The bloodline shouldn't physically mutate them, but the spells might -- when a sorcerer learns Fly, maybe they have the option of growing wings. When a sorcerer casts Fireball, maybe they have the option of making it a cone of fire from their mouth. When a sorcerer casts Fear, maybe they have the option of it radiating from them in a burst. Even if they don't show any outward signs of it, though, a sorcerer with a dragon bloodline will have spells that reflect that bloodline (even if it's not literally a bloodline -- maybe the dragon imparted magic onto them).
Wizards can customize their spell list, and might know an infinite variety of spells.
Sorcerers are locked into their spell list, but might cast those handful of spells forever.
That's the big distinction to me. Books vs. Bloodlines. Classical Beethoven vs. old school beat-boxin'. DaVinci vs. Jackson Pollack. Careful, prepared, methodical, and powerful, vs. spontaneous, rapid-fire, chaotic, and liberating.
See, I find myself agreeing with so much of this that I get a bit of mental whiplash when you come to a conclusion so different from where I get from the same starting points.
To me, the difference between wizard magic and sorcerer magic is like the difference between cooking from recipes or cooking from scratch. The wizard's a recipe follower: the instructions have been written down, and as long as they are executed properly they get the expected results. The sorcerer cooks from scratch. They have an intuitive feeling for the results they want to get and how to get there, but as they're not following set rules sometimes you get the inedible and sometimes you get the incredible.
Or it's like the difference between a trained classical musician and an improvisational jazz musician. The classical musician reads the notation and makes their best attempt to follow the composition faithfully. The jazz musician plays around, with the piece, keeping the core of the melody but
intentionally deviating from a faithful reproduction.
So the idea that sorcerers would and should have a
narrower and more rigid set of magical abilities seems entirely counter-intuitive. The wizard is the structured, ordered, magic user. The sorcerer is the chaotic and fluid one. The word
locked should come nowhere near any description of a sorcerer's magical ability, except as part of the word
unlocked.
I honestly hope (though I think it's a vain hope) that the final version of the sorcerer
doesn't share spells with the wizard's spell list. Sorcerer spells should
never look exactly like a wizard spell.
If you ask the recipe-follower and the scratch-cooker to prepare dinner, you'd be very surprised if they produced
identical dishes.
If you asked both the classical musician and the improvisational jazz player to play a piece of music, it would be perplexing if they produced performances that you could not readily tell apart.
So why then when a wizard and a sorcerer's attempt to produce the same general effect produce
exactly the same effect?
Sure, the wizard might know a spell for every situation, if he's studied enough, and prepared the right ones. But he's rigid: he has to follow the recipes. The arcane is a mystery he studies, not something intuitive and intrinsic. He cannot improvise. If he doesn't know the right spell for this situation, he cannot adapt on the fly.
The sorcerer shouldn't know any spells at all, at least in the sense that wizards know spells. The sorcerer should know what effect he's trying to obtain, but unless it's one he tries for all of the time, he's running on instinct and improvisation to get there. Magic is his lifeblood. To him, it's about what
feels like it will work rather than what some old fogey wrote down in a book 300 years ago. There should be no preparation, no locked lists.
A different mechanic to access the same list of abilities (or a subset thereof) does not, to me, justify the existence of a class. The mechanics should fit the flavour, rather than having the flavour be something grafted on to justify a set of mechanics.
Like I said, though, I don't really expect I'll see what I want. It requires far more effort for them to make and balance, and doesn't have that mechanical efficiency of using stuff developed for another class. (I do find it amusing that while 4E is often accused of "samey-ness", its wizard and sorcerer shared no spells at all, while 3E's sorcerer was an alternate method of casting wizard spells masquerading as a class.)
