I mentioned in a Google plus post that I was working on a conversion of a magic system from USR to Swords & Wizardry. Herein lies that conversion:
The study of magic is covers a vast and largely unmapped scope of knowledge. No individual mage can hope to master it all. Mages, however, have found that highlighted a limited number of areas of study helps them to use the forces of magic in many different ways. By focusing on three or four broad themes of magic, a mage can often successfully research spells that cover a wide range of effects.
These broad themes are called emphases. Throughout a mage's lifetime study of magic, he or she will choose a handful of emphases to guide their study allowing them to create wondrous and powerful magics. These emphases will also make one mage distinct from another. In battle, one mage may hurl small bolts of fire while another uses spears of ices to smite their targets. They may be equally powerful effects, but each mage adds their own signature style.
Mechanics of Emphases
The mechanics of using the emphasis system in magical research are pretty straightforward. A 1st level mage chooses any noun to be their first emphasis. Examples include Fire, Healing, Walls, Blades, Ice, Illusion, Mind, and Acid. The player may also use labels associated with schools of magic used in various forms of the world's oldest RPG. These include Evocation, Summoning, Geometry (2e), Enchantment and many, many more. This first emphasis will be rated as a +2. At each new level a mage gains, he or she gain another emphasis rated as +1 or they may increase an existing emphasis by 1. The limits of increasing an emphasis is determined by the number of emphases a mage already has. An emphasis cannot be raised to +3 until the mage has three emphases. An emphasis cannot be raised to +4 until the mage has four emphases and so on.
To learn a new spell, a mage must research that spell. Successful magic research is determined by rolling higher than the mage's Saving Throw + the level of the spell. So if a 7th level mage wishes to research a third level spell, the mage must roll 12 or above to be successful. The Saving Throw of a 7th level mage is a 9 and the spell is determined to be a 3rd level spell, thus 9 (ST) + 3 (level of spell) = 12.
If the spell attempted incorporates one or more mage's emphases, he or she can use them to increase the roll. In our example, let's say that our 7th level mage has the following emphases: Fire +3, Blades +2, Mind +2, Acid +1. The mage wishes to research a spell that will immobilize 1d4 bipeds of up to human size or one target of up to Hill Giant size. The effect will be that the target will be immobilized because they will see themselves surrounded by a tight wall of swirling flaming swords. The GM notes that this is essentially a Hold Person spell, so he rates it as a third level spell. The mage must roll a 12 or better to successfully research the spell. The mage also gets to add 7 to the roll (Fire +3, Blades +2 and Mind +2 as the fiery swords are perceived only by the targets.)
Since gaining new spells relies on spell research, the ability to research spells is available to mages at 1st level. The cost of such research is level of spell * 300 gp. Researching a new spell requires a number of weeks equal to the spell level to complete. For example, researching a 3rd level spell costs 900gp in materials and will require three weeks to complete research. At the end of this time period, the success roll is made. If the mage succeeds, the spell is added to his or her spellbook.
The other, much larger implication, is that the spell list in S&W serves as a guideline for spells a mage can research. Many spells that will be researched will be very similar to those listed, but with certain tweaks to maximize the mages' emphases. The example noted earlier is, in fact, a Hold Person spell, but a mage with different emphases will display that spell with completely different effects. A Mage with an Acid emphasis may immobilize a target by surrounding it with very real acid. A Mage with an Undead emphasis may immobilize a target by employing a huge bony fist that emerges from the ground. The possibilities are endless.
Scrolls found in adventures can be the generic versions of the spells as listed in S&W. This makes work relatively easy on the GM. But an adventurous GM may decide to randomly determine the emphases of the wizard that created the spell thereby giving it a unique twist.
For the record, adding a spell to the spellbook requires the level of the spell in days to transcribe to the spell book.
Characters can also make scrolls at any level as well as engage in magical research. Making scrolls requires the mage to spend 100gp per level of the spell. It will take one week + the level of the spell in days to create a scroll. For example, creating a scroll of a third level spell would require 10 days.
How This Plays Out
This rule applies to all spell casters in my house rules, even Clerics. Cleric do not require spell research, but their spell exhibit themselves according the emphases determined by their specific deity. Clerics can make scrolls using the same rules as mages. Sorcerers also use their emphases for spontaneous casting of spells - the more emphases included, the greater the chance that the spell will work. (Sorcerers, however, cannot create magic items.) Even Alchemists and Hermetic Magicians gain benefits from emphases. Details will come when those types of magic-users are covered.