There’s Always a Chance: d20 Ability Score Checks in B/X

The topic of rolling 1d20 and comparing it to an ability score to resolve an action has come up a couple of times on Reddit in the past couple of days, and also it’s one I’ve been meaning to post something about. I’ve seen a lot of talk over the years how this is some sort of newfangled thing or not very oldschool-ish, but “ability checks” have been a common thing in Dungeons & Dragons since the early days.

Though I’m not sure about Dragon magazine or modules, I believe the first time this sort of mechanic was directly spelled out in a rule set was in 1981’s Basic Rulebook, edited by Tom Molday. Though, like many things in 1981 D&D, the rule itself is clear but the presentation is not nearly so obvious; it’s in the DM Instructions section on page B60:

“There’s always a chance.” The DM may want to base a character’s chance of doing something on his or her ability scores (Strength, Dexterity, and so forth). To perform a difficult task (such as climbing up a rope or thinking of a forgotten clue), the player should roll the ability score or less on 1d20. The DM may give a bonus or penalty to the roll, depending on the difficulty of the action (-4 for a simple task to +4 for a difficult one). A roll of 1 should always succeed, and a roll of 20 should always fail.

It’s presented a little more obviously (but as an optional rule) in the Expert Rulebook edited by David Coke with Steve Marsh on page X51:

SAVING VS. ABILITIES (OPTIONAL): The DM may want to base a character’s chance of doing something on his or her ability ratings (Strength, etc.). The player must roll the ability rating or less on a d20. The DM may give a bonus or penalty to the roll, depending on the difficulty of the action (-4 for a simple task, + 4 for a difficult one, etc.). It is suggested that a roll of 1 always succeed and a roll of 20 always fail.

(Personally, I like the “save vs. abilities” verbiage and try to remember to use it despite calling these things “ability checks” for decades.)

I’ve also seen (and sometimes used) ability score checks using d6s, usually something like

  • Roll under relevant ability score based on difficulty:
    • Easy: 2d6
    • Medium: 3d6
    • Hard: 4d6
    • Very Difficult: 5d6

This is nice because you can just assign difficulty levels and the ability score in question for various stuff (swimming across the river is a 3d6 Strength check, for instance) and you’re done. But I like the equal-probability of the 1d20 method and using modifiers as needed to adjust difficulty.

I also seem to remember a “multiply the relevant ability score by X to get the d% chance of success” rule, so a PC with a Strength of 14 on a “5x action” would have a 70% chance of success. But I’m not sure where that might have been from. Or if I maybe made that up myself. Because it TOTALLY sounds like the sort of thing I would have done circa 1987.

I am not actually a big user of saves vs. abilities, usually preferring a simple X-in-6 roll on 1d6. But there are times when rolling against a character’s applicable ability score is appropriate and I don’t hesitate to go that route if I think or feel that it’s appropriate in the situation. It’s entirely possible that the non-weapon proficiency system in late 1e and 2e AD&D (which I never really cared for) soured me on roll-under-ability checks.

One place that I’ve been considering using them is a save vs. Constitution as a character’s saving throw to avoid death when falling below 0 hit points. (Kilgore’s B/X calls exactly 0 hit points “incapacitated until the end of the turn” instead of dead, and characters reduced below 0 get one final roll to pull through.) Currently, our “save vs. death” is rolled on the “Death Ray or Poison” column, but since I permit arranging ability scores as desired, a player has a chance to have some say over his or her PC’s ability to fend off the Angel of Death.

However, I’m trying to de-empahsize the importance of ability scores in my game and using saves vs. abilities is bound to INCREASE the value of good scores when I’d rather that players don’t worry about them so darn much.

Finally, I am more and more coming to the realization that it’s easier and (usually) better to just tell a player that his or her character succeeds if it’s something that isn’t very difficult and exact timing doesn’t particularly matter. Sneaking past a sleeping guard might not require a check at all if the PC is alone, careful, and not wearing metal armor. On the other hand, if I have decided that sneaking past that particular guard is going to be very difficult, the attempt will probably fail unless the PC is a thief using Move Silently. Ruling on actions with a simple “yes you can” or “no, that seems pretty unlikely given the circumstances” is quick and easy if you are fair and consistent about it. Of course, if the player REALLY wants to push it on the pretty unlikely stuff, let them try, consider a save vs. ability to resolve it, and let the dice fall where they may.

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