The Triangle of TTRPG System Types

A Core Categorization of TTRPG Systems

Once you breach through the haze of the D&D-sphere, that mental space where D&D is the only system, the best system, and the universal system that works for any campaign idea with some mere tweaks here and there, you will first find out how wrong you were, and then after saying your mea culpas, you’ll have a lovely, expanded domain of TTRPG systems to explore.

Many of you probably already went through that phase, missed it (easier to if you started back in early D&D days and thus weren’t bombarded with magic-users of the seashore content), or perhaps you were lucky enough to start with a different system before learning about or playing D&D.

To aid you in finding the right system, and to establish the basis for when I discuss TTRPG systems in the future, I will explain the triangle of TTRPG system types. Think about each point of the triangle as a different type of action adjudication, the core mechanical component of any TTRPG system. The three are: 1) attribute-based adjudication, 2) skill-based adjudication, and 3) ability-based adjudication. Most systems use two of the three. Attribute systems rely primarily upon a set of core characteristics, core aptitudes, to determine the strengths and weaknesses of each character when they attempt an action. Skill systems use a more-detailed list of skills to represent talent in different domains of knowledge to the same end. Ability systems abstract talent and skill into abilities, or powers, which characters can “activate” to accomplish tasks.

There is another tri-axis upon which to categorize TTRPG systems; systems are either rules-light, midrange, or rules-heavy. So, for example, D&D 3.5 is a rules-heavy attribute/ability system, whereas D&D 5e is a midrange attribute/ability system. GURPS is a rules-heavy skill system, and Mongoose Traveller 1e is a midrange attribute/skill system.

Alright, cool, you have your neat little categorization system… What’s the point of it all?

In order to run the best possible game, you ought to not only understand your players and how they operate but also your system, what it’s supposed to accomplish, and how it does so. If you don’t, you risk working against the through-line of your TTRPG system which can cause burnout or a lot of dissonance between the world you’re trying to portray and the core mechanics of the system. (For example, it is impossible to run a low-fantasy/low-magic campaign using D&D rules, which you might not know until you realize that most ability-based systems in fantasy struggle to facilitate a low-fantasy/low-magic feel at the very least. Knowing that, a cursory glance at any modern D&D rulebook would immediately dispel any thought of the possibility and you would be free to go and find another system.)

Allow me to clarify a few things for definitional purposes. The categorization is of the basic mechanics for adjudication character actions. In a solely-attribute/skill/ability system, you would only (or primarily) consult the appropriate attribute/skill/ability when making a roll to determine whether or not you succeed for an action. Traveller (an attribute/skill system) where for absolutely every roll, you add both a skill modifier and a keyed attribute modifier. Call of Cthulhu errs much more towards a skill system because you rarely make attribute rolls - they are there to set up your character and you derive initial skill points from them, but they do not feature thereafter in actual gameplay that often.

On Attribute Systems

Attribute systems focus on the inherent strengths and weaknesses of each character and then use those to determine how likely a character would be to succeed at a task. Attribute-uber-alles systems tend to be very archetypal - characters are defined by abstract representations of human qualities. For example, in D&D, a twenty-year old, male wizard might have low strength and high intelligence even though twenty-year old males tend to be fairly strong, but because the wizard archetype is that of a mentalist, this low strength, high intelligence, twenty-year old male exists perfectly fine in that system - the attributes don’t represent actual biological aptitudes as much as they represent abstract heroic aptitudes.

If you like this dynamic, then attribute systems are for you. You can fairly-easily create characters with evocative archetypes and you don’t have to spend as much time worrying about what type of character you are playing - if you have high intelligence, you are a mentalist of some sort, likely a wizard, and that is that.

If you attempt to view the attributes as representing actual biological aptitudes when playing or running an attribute system, you will likely face extreme dissonance. In D&D, for example, halflings can have equivalent strength to half-giants - obviously the strength attribute represents something other than a comparative measurement of muscle mass. You can fiddle around with this and find some middle ground where attributes have more realism about them, but ultimately, each attribute will likely represent an archetypal aptitude rather than a biological one.

On Skill Systems

Skill systems try to focus on realism, most of the time. In a skill system, any character can invest in whichever skills they want (typically restricted by a career path of some sort), allowing for more-realistic characters. For example, the warrior in a skill system will have plenty of fighting skills, but they could also decide to spec into archeology because a person in a real world is capable of pursuing both war and archeology if they desired. The wizard in a skill system will have plenty of magic skills, but they could also spec into swordsmanship because again, the skills represent actual training and aptitude in an area of expertise and aren’t pre-packaged.

There is far more customization in skill systems and players can create pretty much whatever character they can think of. That is a double-edged sword for some though. With freedom comes analysis-paralysis, especially for players who come from attribute systems. Once you push past this though, skill systems are the best for customizing characters and having agency over your character’s mechanical progression throughout the campaign.

These systems are also the most flexible because character creation and progression is not shunted down certain archetypal paths. Any path can be forged and embarked upon. If you want a certain genre, you can use pretty much any skill system and just change the skills, for example. Chaosium did this from Basic Roleplaying to Runequest to Call of Cthulhu. R Talsorian did this from Mekton to Cyberpunk to Witcher. Their systems are basically the same but for genre changes and an additional package of mechanics added here and there. This sort of flexibility allows the DM to really take the system into their own hands and make it work for their campaign rather than having to make the campaign work for the system as occurs with many attribute/ability systems.

On Ability Systems

Often coupled with attributes, ability systems are more or less based on video games where your character has certain perks or powers that define their character’s strengths and weaknesses. Necessarily, when you create a bunch of perks and powers, a bunch of abilities, you abstract talents and aptitudes into mini-blobs of gameplay. These blobs are often sorted by “classes” or “archetypes” so that there is some semblance of knowledge domain - i.e. someone who spends a lot of time fighting ought to have fighting abilities and not magic abilities - this makes it so that you must choose from pre-created packages to build your character. The warrior in a skill system is good at fighting because they have a lot of points in fighting skills - the ability system has to translate the skills a warrior would have into a pre-created list of action options, resulting in an abstract and pre-determined set of mechanics a player playing a warrior character can choose from. As an example, in Blades in the Dark (one of the few skill/ability systems), the “Cutter” class, defined as “a dangerous and intimidating fighter” gets an ability which grants them special armor. Other classes can use armor too, but only the Cutter gets special armor.

This adds uniqueness to the archetype of the “dangerous and intimidating fighter” - they likely would be the one to have some more-advanced armor. But in reality, there is no reason why anyone with the proper resources could not also have special armor. Ability systems, like attribute systems (typically in combination with them), sacrifice realism for evocative character archetypes each with certain pre-packaged powers. This trade is excellent for simpler systems since the authors can come up with a few mechanical character packages that are functional without worrying about additional mechanics for customization outside the bounds of those packages. The trade is also excellent for pulpier systems that prize evocative archetypal glory in combat over realism there or elsewhere.

Though I prize realism in my TTRPG games and thus prefer skill systems generally, I find that abilities and powers are tons of fun to play with. I get my fix of ability systems from video games and prefer my paper/pencil RPGs more grounded.

On Other Weird Systems

There are a number of weird systems with completely deranged and heretical mechanics. In some, you don’t even roll dice! Can you imagine that? A TTRPG system where you don’t roll dice! Folly!

In all seriousness, some systems, especially those designed for one-shots or mini-campaigns, use crafty components or even other games for their mechanics. For example, the horror system Dread uses a jenga tower - players pull blocks from the tower whenever their character attempts an action and if the tower falls, they die. Ten Candles uses, you guessed it, candles - as the candles burn out, the character’s doom gets closer and closer. These systems lack longevity - candles don’t last forever and neither do jenga towers - but they are really excellent for one shots and create a wonderful atmosphere during the session.

Bitterblossom’s Picks for Each System Type

Attribute/Ability Systems:

• D&D 1e (The original TTRPG and the version of D&D with the most soul. There are many versions: I recommend Labyrinth Lord by Goblinoid Games.)

• Symbaroum (This is a combat-oriented, dark fantasy system that sports a more grounded realistic feel and a more skill-based progression system.)

Attribute/Skill and Skill Systems:

• Traveller (The original sci-fi TTRPG system, D&D’s brother. There are many editions so take your pick. I like Mongoose Traveller 1e.)

• Call of Cthulhu (Frankly, you can use the D100 ruleset for any genre and it works quite well, so this system might be one of the most versatile out there.)

• GURPS (Everything you need to know about this system is in the name. Expect some crunch.)

Skill/Ability Systems:

• Blades in the Dark (I wouldn’t readily recommend this because it plays very differently than most other TTRPGs, but if you like what it offers, it’s really solid. Regardless, the atmosphere of its setting is phenomenal.)

Weird Systems:

• Dread (A simple and wonderful system for horror one-shots. Best played in a dark room with a lantern for light.)

Obviously, each system has its unique oddities and desires that you must contend with when running or playing it, but you can use this overarching categorization as a solid starting framework to figure out which sorts of systems you want to explore.

I encourage you to try out many systems, see the value they offer and recognize what they are trying to accomplish, and you’ll start to learn what you like best and even what from one system you wish to splice into another.