Bluff/Sense Motive House Rule. Help?

[Jeff the Green]

So, I've been having something about Bluff/Sense Motive bugging me for a while. Specifically, this line in Bluff:

A successful Bluff check indicates that the target reacts as you wish, at least for a short time (usually 1 round or less) or believes something that you want it to believe.
As is occasionally pointed out, that implies that you can convince someone of patently ridiculous ideas, like that the sky is actually green (when they're outside and able to see it's not). That bothers me a bit. What bothers me more is that I like the players to have a bit more agency to decide their characters' personalities and behavior (and me to decide for NPCs), and prefer skills to govern what they know or can do rather than how they behave. If you want to make a person that doesn't trust anyone but can't get the points in SM, your characterization gets broken every time you meet a scoundrel.

Also, there's no way to simulate being certain that someone is lying when they're not

So I thought of some vague house rules, and I'd like some help tightening them up.


As usual, when an NPC lies, the PCs get automatic, secret SM checks.

If they succeed, they detect the lie.
If they fail, they don't.

If a player is suspicious of an NPC's statements, they can ask for an SM check, again secret.
If the NPC is lying:

They get some bonus to their SM check1.
If they succeed, they detect the lie.
If they fail, they don't.
If they critical fail2, they're fairly certain they're telling the truth.

If the NPC isn't lying:

If they beat some DC3, they don't detect a lie.
If they beat some (higher) DC3, they're fairly certain they're telling the truth.
If they fail the DC, they think the NPC is lying when they're not.



I think this will be an interesting mechanic. It makes asking for an SM roll somewhat riskier, but also more rewarding if their SM is high enough to reliably beat Bluff checks. It's also less restrictive than the original idea. Aside from general opinions, though (which I'd appreciate), I have some specific questions (referring to the superscript numbers above):


How big of a bonus? (I was thinking +2 or +4, but I don't really know.)
By how much?
What DC? Should it scale? If so, how?

[TuggyNE]

Aside from general opinions, though (which I'd appreciate), I have some specific questions (referring to the superscript numbers above):


How big of a bonus? (I was thinking +2 or +4, but I don't really know.)
By how much?
What DC? Should it scale? If so, how?


+2 is reasonable, I think.
Failing by 5 is the usual (in the rare cases skills have critical failure rules, such as Climb or Disable Device).
Diplomacy based, perhaps? Add +5 to be fairly sure they're not lying.

[Duke of Urrel]

The System Reference Document does offer some decent guidelines for Sense Motive check bonuses to resist a Bluff check made by a skillful liar. These reflect different degrees of implausibility (slightly implausible +5, highly implausible +10, and ludicrous +20), and they appear in the SRD's description of Bluff skill.

I don't mean to insult you by quoting the SRD at you, but I want to show how it can be a springboard for our further speculations.

One of the problems you mention is game-breaking power. What if an NPC has amazing Bluff skill and a magical competence bonus that makes a Sense Motive check fail even with a +20 bonus? I agree that even an amazing Bluff check should not be enough to make you believe that up is down, that black is white, or that anything contrary to general common knowledge or at odds with what you can immediately perceive is somehow true. Maybe you might be persuaded for a few moments that a red dragon really does want to make friends, but this delusion will be quickly dashed to pieces when you actually meet the dragon.

On the other hand, in a magical world, very few claims about reality are absolutely impossible to believe. So a very good Bluff check should persuade anyone to believe almost anything, at least for a few moments.

[ArcturusV]

Well, as someone once said, "It's not what you say, it's how you say it". I've, in real life, gotten away with some pretty damned wild bluffs. Even "Impossible" ones as you mention which have gotten people to go look. Particular examples that come to mind from my real life are:

In July (Northern Hemisphere, nearly sea level, around the 45th parallel on the west coast of the US), I once told my sister, "WAKE UP! WAKE UP! IT'S SNOWING!" and 2 minute later she was running for the door going "SNOOOOOOOW!" before she realized how impossible that was. It wasn't like I took advantage of an ignorant child either, she was 12 at the time.

Camping in the Cascade Mountains I was rough housing with my older brother. He had me knocked down, was dragging me off by my foot. In a sudden moment I pointed behind him and (Oddly convincingly) said, "HEY LOOK! A WHALE!" and he turned to go look at it for just enough of a distraction for me to get my foot free, stand up and get out of arm's reach.

I mean as silly and stupid as it sounds... bluff shouldn't have to be "plausible". And I think that's the sort of things the Bluff skill really is meant for. This isn't telling someone the sky is green and have them going around thinking the sky is green for the rest of their life. It's making them go, "Really? Did the Archmage screw something up?!" and looking out of the window. So the homebrew rules aren't quite as needed.

I would apply those to Diplomacy however, as Diplomacy is long term lying typically and trying to keep someone in the dark about a truth.

[Duke of Urrel]

The question of how to confirm when a NPC is telling the truth is different, because the SRD doesn't discuss it anywhere, to my knowledge. This is not as great a problem as opposing the Bluff check of a liar, because there's nothing stopping a PC from believing a NPC if the NPC isn't even trying to lie. The question is only this: How easy should it be for a PC to discern that an honest NPC is in fact trustworthy, especially if the PC's first hunch is that the NPC is a liar?

The SRD sets the Sense Motive DC for confirming a hunch at 20. Maybe this works the other way, so that if a PC is suspicious of a NPC who is actually honest, making a Sense Motive check at DC 20 clears the suspicion away. Any score less than DC 20 would leave the suspicion intact. If you like, you can make this Sense Motive check secretly for the PC, so that if it fails, the PC's false opinion remains unchanged (because the PC can see no reason to change it).

Here's another idea. Maybe convincing someone that you actually are telling the truth requires Diplomacy skill. So if a truthful NPC makes a Diplomacy check at DC 20 (let's say), the PC's suspicion is dispelled.

Or you could combine these two ideas. If either a PC's Sense Motive check or an honest NPC's Diplomacy check succeeds at DC 20, you can say to the PC: You are confident that this NPC is telling the truth.

These roles can also be reversed. Suppose a NPC is naturally suspicious of the PC, perhaps due to some racial or cultural prejudice. By making a Diplomacy check at a certain DC (maybe enough to improve the NPC's attitude to Indifferent or Friendly), the PC can dispel the NPC's suspicion, at least enough so that the NPC believes the PC is telling the truth in this particular instance.

I consider it my own personal rule that you can use Bluff skill only to deceive, and you can use Diplomacy skill only if you are honest. In other words, when you make somebody an offer and use Diplomacy skill to persuade somebody to accept it, you have to be serious about making the offer. (Yes, there is a Bluff synergy bonus that you can add to Diplomacy checks, but this only reflects your ability to be patient and polite while negotiating with someone who's being such a stubborn jerk that you would much rather wring his neck.) If you're secretly intending to cheat when you make an offer, your offer is a lie, and you have to use Bluff skill to make it credible. (So as you can see, my opinion of what Diplomacy can achieve differs from ArcturusV's opinion.)

[Duke of Urrel]

One more thing. A DM doesn't want to make it too easy for PCs to figure out that an NPC is lying, simply by means of meta-game thinking. Whenever PCs talk with a new NPC who may or may not be untrustworthy, it's a good idea to make some "dummy" Bluff checks even if the NPC is actually perfectly honest. If you make Bluff checks only for deceitful NPCs and never for truthful ones, PCs will quickly figure out whom they can trust and whom they can't, and it shouldn't be that easy.