[RPG] general rule of take the average or roll the dice

dnd-5e

There was a comment on one of my answers that stated that all instances of average or dice rolling are treated the same by the rules. Specifically mentioned are players gaining HP, Monster Damage and Passive checks.

For Monster Damage in the DM Basic rules (page 6 v0.1) it reads:

Hit. Any damage dealt or other effects that occur as a result of an
attack hitting a target are described after the “Hit” notation. You
have the option of taking average damage or rolling the damage; for
this reason, both the average damage and the die expression are
presented.

For player's gaining hp when they go up a level in the Basic rules (page 10 v.01) it reads:

Each time you gain a level, you gain 1 additional Hit Die. Roll that Hit Die, add your Constitution modifier to the roll, and add the total to your hit point maximum. Alternatively, you can use the fixed value shown in your class entry, which is the average result of the die roll (rounded up).

Passive checks explicitly states that you do not ever involve any die rolls. (Basic Rules V.02 page 59)

A passive check is a special kind of ability check that doesn’t involve any die rolls. Such a check can represent done repeatedly, such as the average result for a task
searching for secret doors over and over again, or can be used when the DM wants to secretly determine whether the characters succeed at something without rolling dice, such as noticing a hidden monster.

The one other place the concept of taking an average vs rolling dice comes up is with Rolling Stats for PCs there it makes it very clear (and is arguably not really the average)

You generate your character’s six ability scores randomly. Roll four 6-sided dice and record the total of the highest three dice on a piece of scratch paper. Do this five more times, so that you have six numbers. If you want to save time or don’t like the idea of randomly determining ability scores, you can use the following scores instead: 15, 14, 13, 12, 10, 8.

Is there a general rule that can be derived here, (Are there enough data points in the rules to create a general principle?) or is the different use of language in all the instances make them all unique situations which need to be interpreted independently?

Additionally, if there is a general rule, can it be used anytime you want to "save time" or "reduce randomness"? (And if not, why not?)

Best Answer

Yes, the general rule that can be derived is that it's either-or: Either roll, or pick; not both roll and pick and then choose the best one or some other permutation that includes extra decision steps not described.

D&D 5e is written in "natural language", which is disparaged in some edition-warry parts of the Internet right now, but only means that the game is written so that the most obvious reading is generally going to be the right one, so that the game is understandable to the majority of readers who never read errata or participate in online debates about RAW, RAI, LFQW and other jargon.

In a natural language reading of all these rules, you either pick or roll, not both. If you were meant to do both, it would clearly say that, because not clearly saying that you're supposed to do both would be misunderstood by the majority of readers, if that was the intent. Since it doesn't say to pick and roll and take the best, the normal interpretations of "or" and "alternatively" are in force: either-or.

Extending the general principle of "when the game says to pick or roll, you pick or roll but not both" to other circumstances in the rules is a non-starter, because it just doesn't apply to any rules that it doesn't already apply to.


That principle isn't what your last question assumed would be derived though, so for completeness, let's now address the general rule that it assumes could be derived: that any roll could be instead replaced by taking the average, maybe if you want to save time or reduce randomness.

Extending "take the average" to other parts of the game where it's not mentioned as an option could be done as a house rule. It would probably not break most uses, and would likely find some corner cases where the extra predictability would break things and produce something that is off the average, but you'd have to play with the house rule for a while to find those, as is usual houseruling procedure.

  • Off the top of my head, it would definitely break to-hit rolls. If nothing else, this is the clearest counter-evidence to suggest that it could have been meant as a derivable general rule.
  • As an example of taking the average producing subtly skewed, non-average results, a wild magic sorcerer who knew that they could take the average damage of a surge effect might end up risking surges more often, thereby producing them more often than they would on average if all the involved rolls were actually rolled.
  • Similarly, not rolling for healing means you can attempt to plan farther ahead knowing not only your current resources exactly, but also one step ahead into the future of your resources with reasonable accuracy. This would alter decision-making, skewing play in who-knows what different direction.