de modulii magicii

This is a thinky post and modest proposal about modularity in TTRPG design.

Since modularity can mean a lot of things to a lot of people, I'll be specific. I am not talking (at least not directly) about the role that discrete packages play in character customization; I am talking about the more general organizational principle of giving a unique name to a particular rule and referring to it at need elsewhere in the text.

When a rulebook describes a number of statuses that can affect a character's combat options: blinded, dazed, deafened, prone, surprised, stunned and so on, and then elsewhere gives players and enemies the option to blind, daze, deafen, knock prone, surprise and stun one another, that's an example of modularity. Modularity is a strategy for sacrificing some amount of clarity (the consequences of stunning a foe may not be explained in the same place in the text as the source of the condition) for to make the rules more consistent (all abilities that stun foes achieve the same effect) and concise (it is not necessary to quote a modular rule everywhere it is referenced). The cost in clarity can be offset by choosing descriptive names for the modular rules so that readers' expectations about what applies to stunned characters map well onto what the actual rules provide for those situations.

A place where modularity is particularly useful is in magical effects. By nature, magical affects are at least somewhat contrary to the readers' expectations and, if precise boundaries of the effect are needed, a lot of text may be the result. Delta has a whole series of posts analyzing the rules texts of spells from Chainmail through 3E; it's evident at a glance that spells have accumulated more and more text as time goes on and the attempt is made to nail down exactly what such and such a piece of magic can do.

Whether you like detailed spells descriptions or vague ones, is not practical to quote the full text of a spell description every time it is referenced. As such, the rules are full of effects defined in reference to specific spells. An unscientific survey of a pretty orthodox old school magic item list had 10-40% (depending on category) of magic item listings specifically referencing a spell effect. Excluding scrolls (which are mostly spell scrolls), potions are next most likely to reference spell effects, followed by wands, miscellaneous items and finally rings. Monster abilities in early editions and their imitators seem much less likely to reference spell effects; however 3/3.5E can't get enough of monster abilities directly referencing spell effects, between traditional spellcasting, spell-like abilities and the very confusing situation of "supernatural" (and sometimes "extraordinary") abilities that duplicate spell effects without certain features of spells such as the possibility to be interrupted or dispelled.

Honestly, I think 3/3.5E is pushing in the right design direction there, even if they did it in the messiest possible way. Nevertheless, I'd wager few people have the system mastery to accurately tell you off hand the differences between a spell, spell-like ability, supernatural ability and an extraordinary ability. And even fewer would be able to accurately guess the effects of an unfamiliar spell from its name. In 4E, the designers pulled hard in the opposite direction by removing the modularity from spells (and prayers and maneuvers and psionic powers) entirely: all abilities got siloed to the class or monster type that granted them where they are described in full. In particular, this means that while the information is conveniently organized for the DM running the encounter, the economics of space and how many unique abilities a DM can actually keep in mind while running the encounter suddenly place pretty hard limits on how intricate monsters can be.

Rather than continue talking about the historical vicissitudes of spell modularity, I will instead make a modest proposal:

Modest Proposal

Keep magical causes and magical effects separate:

• A magical effect (wonder) should be listed under a descriptive name and any limitations that are not obvious spelled out (for example, that the wonder of move earth can shift loose earth and its vegetation, but not stone).
• A magical cause could be a spell that can be learned, a consumable preparation, an artifact or a natural ability of a magical creature. The description of a cause should name the wonder should spell out any important limitations on its use (costs, concentration, durations, number of targets, ranges, time to activate and so forth).

Different ways of working the same wonder can be made to feel very different if, for example, different costs are demanded from a holy person and a necromancer to bring about the same healing of a broken body. The details of the wonder equip a ref to rule on its applications and edge cases, while the details of the causes are able to be more diegetic and flavorful without sacrificing modularity for that.

A book of wonders could be used by a referee both as an at-the-table reference for whatever magic is in play but also as a source for describing new wizarding traditions (by selecting a set of wonders and describing that tradition's means of causing each), artifacts or creatures. If the rules texts were sufficiently concise, a deck of cards bearing wonder descriptions could be physically handed out to players when they become able to use them.