I have noticed that a lot of published adventure materials (as well as the Core Rulebook) instruct that opposed rolls be made:

Perception vs. Stealth

Sense Motive vs. Bluff

etc., etc…

But aren’t they actually unnecessary? Can’t we just treat one of the “rolls” as a flat DC?

Let’s take a Sense Motive roll as an example. An NPC tries to lie to a PC. For simplicity’s sake, let’s assume the NPC has a +0 Bluff modifier, and the PC has a +0 Sense Motive modifier.

If you treat it as simply a DC 10 skill check **(DC 10 + opposed skill modifier)**, then the PC has a 55 percent chance of succeeding. I don’t think this changes with opposed rolls.

To illustrate further, let’s say we want to invent a dice-rolling game in which I have a 50% chance of winning. Either you and I can each roll a d20, and I win if my roll higher than yours and we re-roll if we tie. But what’s the point? I might as well roll a single d20 and win if I roll 11 or higher. (Or flip a coin!)

Basically, rolling *two* d20s seems like doing double duty. And since skill checks are not automatic successes on a 20 or automatic failures on a 1, nothing is added or subtracted to the possibility of success by rolling d20 twice.

I see this also applying to Perception vs. Stealth rolls. HOWEVER, it doesn’t necessarily work when the skill you are trying to “beat” is being practiced by multiple creatures. I suppose the rules intend the party to detect the LEAST stealthy individual among a group of hiding creatures, thus adjusting all the probabilities. However, as a GM I skip all this because it’s too much work for little payoff (and it makes Stealth checks too easy to defeat) — and so I just have the PCs do Perception checks against a flat DC.

Conversely, if an NPC is trying to detect whether a PC is bluffing, I don’t see why the PC should just try to do a Bluff check against a flat DC based on the NPC’s Sense Motive modifier.

So I don’t see where opposed rolls are necessary. Or am I missing something?

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## About ronaldsf

Grandmaster of the Pathfinders' Guild at Martin Luther King Middle School.

PC vs NPC I agree with you. If you have two PC’s involved (I want to pick a party member’s pocket) than I think opposing rolls are needed.

Yeah, I agree, just to give the players a chance to roll. Nothing changes probability-wise while the players each get a feeling they got to do something.

3.0 Psionics had a similar issue, where they gave the caster a d20 role as a base DC for his abilities, rather than 10. They took it away soon after in 3.5 and Pathfinder.

The flat DC is simpler, and it leaves fate in the heroes’ hand. Don’t be bound by it, however.

When it serves the story better, the hero’s skill should be the DC and the DM should roll. Lying to the King’s Paladin Bodyguard? I role, the player sets the difficulty. Sneaking around to the spellcaster when you’re allies continue to fight the enemy horde? I don’t want the thief to know whether he’s hidden or not. He’ll only know that by the monsters’ actions during their turn (or their reactions to his failed stealth).

It also cuts out that old stupid question, “Do I know I rolled a 5 on Stealth and he’ll see me before I pull off the backstab? If Billy’s Fighter can see me, I know I failed and I should run.”

For run of the mill battles and events, let the players have the dice. When the heroes shouldn’t know the result automatically (e.g., Bluff, Stealth), it often improves the atmosphere and suspense of the game if you roll the dice, but skip the opposed rolls whenever possible.

Again, like Jason says, player vs player or complex skill checks with many people rolling to beat one another will still take the opposed check. At least there it makes sense.

Yes, story and excitement trump!

And rolling secretly is a good tool for skill checks that aren’t traditionally opposed checks, such as Perception rolls to detect a trap.

I’m not so certain it does not make a difference. The example you chose: +0 bluff and +0 sense motive works out to the same results, but let’s say it is instead +0 bluff vs +10 sense motive.

If you choose 10+mod, then the static DC for the bluff check is 20, or one chance in five, or a 5% chance. If both PC and NPC roll though, the PC may roll between 1 and 20, while the NPC may roll between 11 and 21, and any of these combinations may happen, for a total of 400 (20 x 20) combinations.

Now, if the PC rolled a 14 and the NPC rolled a 3, for a total of 13, then the PC succeeds. In fact, he succeeds if the NPC rolled a 1, a 2, or a 3. In other words, for any result X above 10, he succeeds X-10 times out of the 400 possibilities.

Let me try to make it a bit clearer. The PC has 20 possible results, for which the NPC has 20 possible results. (1) All PC results below 11 will lead to a failure, no matter what the roll is, except if the NPC rolls a 1. (2) All PC results between 11 and 20 (so 12 to 19) will result in a success X-10 times. And (3), all PC results of 20 will succeed no matter what.

So in our +0 vs +10 example, we have the following for the 400 possible combinations:

(1) 20 successes (NPC rolled a 1);

(2) 44 successes (2+3…+9);

(3) 20 successes.

For a total of 88 possible successes out of 400 combinations, or 22% chance of success.

Now, maybe I missed something, but I’d say allowing for NPCs to roll allows for them to score low and therefore give more chances, IF the NPC’s modifier was higher than the PCs.

Somebody should check my math though…

I’m not sure if your numbers are completely right, since skill checks in Pathfinder don’t auto-fail at 1, but I understand the overall point and I think you have successfully refuted my post:

– Yes, there are 400 possible arrays of results from the 2 opposed rolls. So 400 is the denominator of our fractions.

– Using a flat DC, yes the PC has a 5% chance of succeeding at a Bluff.

– Using opposed rolls, if the NPC rolls a natural 11 through 20, there is zero chance the PC succeeds.

– If the NPC rolls a natural 10, there is a 5% chance the PC succeeds (1 combination)

– If the NPC rolls a natural 9, there is a 10% chance the PC succeeds (2 combinations)

– If the NPC rolls a natural 8, there is a 15% chance the PC succeeds (3 combinations) …

– And so on and so on, until the PC has 10 possible die rolls that can defeat the NPC rolling a natural 1 (total 11).

– So 1+2+3+4+5+6+7+8+9+10 = 55 combinations

– 55/400 = 13.75% chance of succeeding on the Bluff

I think a general principle at play here is that increasing the variance lessens the advantage of large numerical bonuses. The more variables you put in, the more important they are relative to the constants.

So YES: it does make a mathematical difference to make opposed rolls! But whether smoothing play at the table is worth the loss of variance is a decision for the GM to make.