Is it incorrect to use Passive Insight to tell Players what their Characters already know about NPCs?

Question

I have a party of 4 noobs, 1 is a pro on other games but new to 5e (like myself - but I haven't played in years), 3 are actually playing their first characters ever. Ages run from 13 to 50 (I love a challenge).

I don't like telling players what they can and cannot do if the rules do not explicitly state it, but I also hate to bash new characters for new player naivety. I also try to keep house rules to a minimum (just to make it easier for them to learn the basic rules). So I kind of "chose" to read the Passive Insight score as a social version of the Passive Perception which can "determine whether anyone in the group notices a hidden threat" (PHB Ch.8).

One of the PCs, a 1st-Level Rogue, was setting a trap for a Slaver Ship Captain & Crew to aid the City Guard. To add to the tension, I had the Captain make a snide reference to the human cargo as 'commodities.' The Player, morally offended, snapped back, "shut up you freaking idiot." Caught off-guard, I asked for his Passive Insight and responded, "With your knowledge of the underworld, you know insulting him like that in front of his men will require a violent show of authority. You can say that, but are you sure you want to?"

A little later the same Player went to strike a final blow to a surrendering NPC while others were striking to incapacitate. I did the same thing, ending with, "Your character has been around enough to know that executing a defenseless man in front of the guard would be murder. They might not notice, or they might let it go, but maybe not. Do you want to kill him or knock him unconscious?"

I'm willing to let the Players do the wrong thing and suffer consequences, I just want them to know the consequences ahead of time. The worst part is that I already know the score - it's on the inside of my screen along with his AC & HP, I'm only asking to make it come from his character's mind instead of my mouth. Of course, I fear that come will across as passive-aggressively robbing them of agency - which is why I've only done that about 3 other times in 13 sessions so far.

My question is, am I actually within the rules by doing this?

Bonus question: Is this a actually a spineless way to force character behavior while pretending like I'm giving them free will?

Answer 1

This is within my reading of the rules, although the choice of Wisdom might not be the best choice of abilities to key this off of. Whether it's a good idea or a covert means of control is a personal judgment, but I have some helpful guidelines I use.

I'll address all of these below.

Is this within the rules?

This depends on how strictly you want to interpret the rules, and how much leeway you think strict rules give you. I think the key section of the PHB is on page 175:

Using Each Ability

Every task that a character or monster might attempt in the game is covered by one of the six abilities. This section explains in more detail what those abilities mean and the ways they are used in the game.

Standard uses for each stat are given immediately afterward for each of the six skill. In each section, though, a passage like the following exists:

Other [Ability] Checks: The DM might call for an [Ability] check when you try to accomplish tasks like:

(For some reason the formatting is off for Constitution checks, but the text is there.)

So I think it is pretty clear that the typical usages given in those long passages are not meant to be exhaustive, but are merely the most common and easily codified. The rest are up to the DM's interpretation and judgment.

I suppose someone could take the attitude that anything not spelled out directly in those examples is off-limits, but I think that's a bad way to read the rules.

Is Wisdom The Right Passive Skill?

It is one of two good choices. The other is Charisma, and while I personally would use Charisma, I don't think Wisdom is so obviously superior that using Wisdom is wrong.

The uses of Wisdom involve observation and understanding of the world around the character, and the typical uses and examples-- animal handling, observing undead, observing threats-- seem to favor the physical world or the natural world. But, Insight (under Wisdom) does explicitly call out dealing with creatures, detecting lies, etc.

The uses of Charisma, however, all center on social and personal interactions, making an informal and fuzzy distinction between the physical world and the social world. They examples you gave all seem to me to be social interactions, and I would tend to trigger than on Charisma.

Is This Backdoor Railroading?

It definitely can be. However, I can't recall the last time I played in a game, 5e or other, where the DM did not use some sort of approach like this at least once in a while. I do this, and I make no apologies for it.

I justify this to myself by remembering that when I GM, especially in a homebrew world, part of my job as GM is to set the tone of the game: It is my affirmative choice to run a world that (say) embraces or rejects a wandering murderhobo motif on the part of the characters. And while I can (and do) address this in pre-game talks and session zero exercises, I do also occasionally need to convey this information-- this social knowledge the PCs already hold-- directly.

I don't even roll for it, if I don't want to. An occasional pre-emption and offer of retcon is better, in by judgment, than letting the game world beat up on my PCs because of their players' ignorance, or our collective mismatch or expectations.

That said, the key word is occasional. If I find myself doing this multiple times per session, and many sessions into the game, then either I'm doing something wrong, or my players aren't taking me seriously, because they aren't modifying their overall behavior.

I try to use my heavier-handed DM techniques (and this is definitely one of them) more at the beginning of the game than any other time. I try to consciously draw down the usage of those heavy-handed over time, so that they don't become intrusive, or a crutch, or (as you fear) a way to manipulate the players.

And to keep myself honest, I tell that to the players: "Hey, guys, I may need to pour social knowledge into your heads for the first few sessions, just to establish the scene. But that's lame, so the more you pick up on it, the less I'll do it, and the happier we all will be."

Answer 2

I think it is not only good but necessary to tell the players things that their characters would know as people existing in the world of the game. It is not substantially different from giving them sensory descriptions of their characters' environment. If you give the players more information and they decide to change their proposed action, that's still their decision. If they hear the consequences and decide to proceed anyway, that is also their decision, and you should be ready to let that play out.

Answer 3

You can DM however you want, but...

It is good to let players make informed choice, but informing them after they made their choice and then letting them retcon their action doesn't leave a good taste in my mouth.

2 things I try and avoid in my games is telling players what their characters think/feel, and when PCs observe something I do not explain what it means or how they should interpret it. In my opinion this robs players of their autonomy and insults their intelligence.

Are you within the rules? I think your choice of abilities scores is a little off the mark, and you break the flow of "DM describes the scene -> Players pick actions -> DM narrates the result of the actions".

Is this a way to remove player free will? In my opinion, absolutely. Asking "are you sure?" is inevitably interpreted as "don't do this."

Show, not tell

While you can have the players check for pre-existing knowledge, you may want to instead have them learn while playing. Show that defiance isn't tolerated in the underworld, instead of having the PCs already know it. If you wanted to establish this fact, all you had to do is have an NPC get whipped for not following orders while the PCs watch.

Insight may not be the right stat

Generally Insight is used for figuring out what someone is thinking. Be it whether someone is lying, or predicting their next move.

In the case of the captain, you might use passive insight in this way: "After you insult the captain, he clearly looks infuriated and places one hand on the whip he has tucked in his belt. The crew around the deck hush each other and look on nervously."

Knowing something may fall under intelligence or be local knowledge that everyone knows.

Explicitly telling players things they can plainly observe may not be a great idea either

Your player observed everyone else incapacitating enemies in non-lethal ways. They know the guard is there, and they know their enemy is defenseless. You don't need to tell them "Your character has been around enough to know that executing a defenseless man in front of the guard would be murder." - they know that, everyone knows that!

A better course of action could be to have the guard interrupt the player's coup de grace, or allow the player to do it, but force them to deal with the consequences.