When you play Fifth Edition Dungeons and Dragons long enough (especially from the DM side of the screen), you’ll start to notice some patterns in the game’s design. The most powerful magic items always bestow no more than a +3 bonus to attack and damage rolls. You almost never see the upper limit of a player’s ability score go above 20, and even from monsters they cap at an absolute ceiling of 30. No matter how many numbers you try to stack, there’s a limit to how high you’ll get your attack bonus to hit and how many hit points your character can build to. So why limit these numbers? What’s the difference between the bounded accuracy model of 5e and the treadmill model of Pathfinder? Which one is preferable, and what is the upside and downside of each?
First, let’s dive into the term “Bounded Accuracy”. Like I stated earlier, no matter how savvy you are character building, your bonus to hit can only be so high. In 5e, the upper limit to a reasonable player’s bonus to hit is fairly standard, and the upper limit to a creature’s armor class also tends to be set. Heck, even Tiamat, a literal god in Faerun, has an Armor Class of 25, meaning that anything with a higher AC has a higher AC than a god. What this does is give even lower level creatures a reasonable chance to hit a much higher level creature, even if that chance lowers with a wider power gap. It means with favorable luck (and tactics), even a lower level party can potentially defeat a much greater enemy.
Let’s compare this to the “treadmill effect” of similar d20 systems. For example, in Pathfinder, certain creatures can have ACs in the upwards of 40s, and the system rewards mathematically minded players to combine as many features as possible to create a statistically superior character with the right choices. What this ends up meaning is that a low enough level character has virtually no chance to hit a creature with a wide enough power gap. A goblin just plain won’t hit a player of a high enough level with a high enough AC. And while Pathfinder has a bevvy of conditional modifiers a clever player can take advantage of in order to close that statistical gap with careful planning, ultimately the odds are still stacked against the lower level combatant.
So let’s look at the pros of a treadmill model first. It rewards players with an exhaustive understanding of the rules (given that your table is playing by the rules-as-written, which most Pathfinder games I’ve heard tend to do) and by making optimized characters. Of course, the cons are that the encounters that a Game Master can use are bounded in scope. At one point, if the minions of one tier are no longer valid threats, they have to use minions of an appropriate tier. The minions have to keep up with the players, which may feel forced or may not make sense in the context of the world.
The pros of a Bounded Accuracy model like D&D are that the numbers tend to be simpler. Rather than having players focus on mechanical advantages they can leverage to statistical superiority, a bounded accuracy model brings the focus of play to description and effects, and although numbers are relevant, oftentimes it's the qualities and conditions of the pieces in play that make D&D combat engaging. A goblin has the possibility of hitting a 20th level player character in 5e, meaning they can still present a threat in high numbers or if they get to attack with advantage. The con of course, is that players that use quantities to measure their character’s power may not be rewarded for optimizing their character. After all, especially when using standard arrays, there are only so many “optimized” builds you can create in 5e’s system.
In his series Happy Fun Hour, Mike Mearls once said that “the more small choices you give players when making a character, the more small schisms in power you’re creating”. To find evidence of this, look no further than 5e’s Feat system in comparison to Pathfinder. In Pathfinder, feats are small bonuses to your character you get every other level (at least from what I can remember, I have a very obvious bias here). In 5e, Feats are larger packages of benefits you get every fourth level, meaning that 5e characters usually only get five opportunities to customize their characters in this way. These larger choices mean that the schisms in power are also less in number, and more importantly, more obvious. I’ve had plenty of conversations with Pathfinder enthusiasts that to make some character concepts work, there is a specific chain of feats needed. While some may argue it exists in 5e, the need is far smaller.
So Why Do We Care?
Great question. I mean, like I say in most of these, it’s the question to end all questions.
My answer is that understanding the design process behind a game system allows the adjudicator of that system (in this case the Dungeon Master) to deliver an experience with greater skill and information. If a DM understands that only the most powerful creatures of a realm have an AC of 25, it gives them a reference on how strong a creature they create is in relation to the party in a more meaningful way. If a DM wants to create custom content, including magic items, subclasses, or custom features, they know how to balance that content in relation to the system.
As silly as it sounds, creating a +4 magic weapon in 5e actually breaks the system, whether you agree with it or not. It breaks the upper limit of the Bounded Accuracy model the system is intentionally designed with, and if you try to fix this break with stronger monsters, then you risk changing to the treadmill model of Pathfinder, and the focus of the game changes.
Bounded Accuracy exists so that players will actually think less about the game’s math and more about the game’s story. 5e’s mechanics are intentionally simple and flexible to allow DMs to deliver custom, satisfying experiences to their players. The mechanics are a tool, not the experience, and by understanding the design process, it empowers a DM to create their own custom content to deepen their world without breaking the system that’s been so elegantly crafted for them.
That isn’t to say you should never mess with rules or purposely break your own system to deliver a specific experience: it just means if you break the rules, you’re doing so intentionally with knowledge of some of the consequences of doing so. I’ve played with +4 and +5 weapons before, and it leads to disastrous power gaps that invalidate the stories of other party members. (Now putting such abilities on some kind of charge mechanic…)
So that’s all I have to say on Bounded Accuracy for now. Hopefully this gives y’all something to chew on, especially for the creative DMs out there.
Study Hard, Play Hard
Professional Game Master musician, music teacher, game designer, amateur bartender, and aspiring fiction author.
Honestly, I write what I want when I want. Often monster lore, sometimes miniature showcases, and the occasional movie/show review.