Benefits (and Drawbacks) of Compatible Math Between RPG Subsystems, Pt. 1

Most ttRPGs have subsystems to handle different tasks a character might attempt, or threats they might need to overcome. For example, a game might have a rule for seeing if an attack hits a foe, a different rule for seeing how much damage it does, and a different rule for efforts to heal the wound over time. Often these rules have some sort of mathematical underpinning tied to a random number generator (dice cards, and so on) that determines success. Sometimes the systems have compatible math… and sometimes they don’t. In this series of essays we’re going to look at the pros and cons of having subsystems be mathematically compatible, and what kind of design pressure may lead to each system.

Now, to be sure, these trends of mathematical subsystems that interact with some randomizer to generate values of success and failure are not universal. Some games have only a single system and it applies to the success or failure of everything. Others manage to model success without randomizers, or even math in general. As a result the observations in this essay don’t apply directly to all ttRPGs, but only to a (broad) subset of them. For example, Lords of Gossamer and Shadow is a diceless system that uses math differently than, say Fantasy AGE. Similarly, Dread does away with random success chances in favor of a tension-building minor physical challenge, and while it’s not quite accurate to say it’s math-free (as having to do something once, vs having to do it twice, is a mathematical concept) it certainly isn’t using math the way most ttRPGs do.

However, even if these game systems don’t interact with math and randomizers in the same way as the items I’ll be discussing in more depth, that doesn’t mean some of the same pros and cons may not apply. Especially for people interested in modifying existing systems (or wanting to try their hands at designing a system from scratch), thinking about how different kinds of tasks are resolved, and whether those resolution mechanisms should be based on the same underlying rules, is useful regardless of what the game mechanics in question are.

I’ll also note that I find examining lots of different game systems useful to gain a greater toolkit of ideas and mechanics I can use for my own designs. While some mix-and-matching might feel weird (I wouldn’t recommend adding a Jenga Tower resolution mechanic to a card-based ttRPG game… at least not in MOST cases…), often being aware of a wider range of designs can help inspire new solutions to old problems (or, at least, help see potential problems and unintended consequences in advance).

Like this kind of multipart game design analysis? Want to see me answer more kinds of questions? Back my Patreon, for as little as $3 a month, and you can suggest topics for me to tackle!

About Owen K.C. Stephens

Owen K.C. Stephens Owen Kirker Clifford Stephens is a full-time ttRPG Writer, designer, developer, publisher, and consultant. He's the publisher for Rogue Genius Games, and has served as the Starfinder Design Lead for Paizo Publishing, the Freeport and Pathfinder RPG developer for Green Ronin, a developer for Rite Publishing, and the Editor-in-Chief for Evil Genius Games. Owen has written game material for numerous other companies, including Wizards of the Coast, Kobold Press, White Wolf, Steve Jackson Games and Upper Deck. He also consults, freelances, and in the off season, sleeps. He has a Pateon which supports his online work. You can find it at

Posted on December 22, 2020, in Game Design, Writing Basics and tagged , , . Bookmark the permalink. Leave a comment.

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