Using the Rules Better: Perception and Investigation
There’s no end of confusion and controversy about what Wisdom(Perception) and Intelligence(Investigation) checks mean in D&D 5th Edition. It seems like everyone has a different take on the issue. Well, I have a different take as well… the difference is that mine is actually useful in practice, rather than just a lot of vague declarations about how the skills are different in some conceptual way. If you want to learn how to use Perception and Investigation effectively in your games, instead of just thinking deep thoughts about their underlying meaning, this article is for you.
How We Walk the Party Line
First off, I fully realize that the skills are Wisdom(Perception) and Intelligence(Investigation), but I’m just going to call them Perception and Investigation, because that’s what everyone says anyway, and it uses fewer pixels. That being said, the fact of the matter is that nobody really seems to have a useful take on how these skills are supposed to be different. That’s not to say that there aren’t plenty of opinions being voiced out there. There are many, and some of them are being voiced very loudly indeed. Most of them just aren’t useful, by which I mean able to be used by actual DM’s when running actual games.
We don’t need qualitative analysis here, or cleverly worded statements about how to think about Perception and Investigation. We need to know how these skills need to be used, because thinking about what they mean doesn’t make games run. A lot of DM’s just let players use whichever one they happen to have whenever they need a check for noticing something in an area, and that’s understandable: you get a lot of vague declarations of how Perception and Investigation are different, and how they differ, but those declarations don’t provide a system through which the skills can actually be used.
Before we go any further, let’s take a look at the biggest and most important of the vague declarations. We might even capitalize that and call them the Vague Declarations, because they come straight out of the Core Rulebooks. I’ll paraphrase a little bit, since some of the passages are fairly lengthy, and because if you’re really interested you can always look them up yourself. They’re easy to find, because they are each in a section about how to use ability scores, right there in the table of contents. I think we both know at this point that you probably won’t look them up right now, so here’s what they say:
The Player’s Handbook Says:
“When you look around for clues and make deductions based on those clues, you make an Intelligence(Investigation) check.”
“Your Wisdom(Perception) check lets you spot, hear, or otherwise detect the presence of something. It measures your general awareness of your surroundings and the keenness of your senses.”
The Dungeon Master’s Guide Says:
“A character with high Wisdom but low Intelligence is aware of the surroundings but is bad at interpreting what things mean. The character might spot that one section of a wall is clean and [not?] dusty compared to the others, but he or she wouldn’t necessarily make the deduction that a secret door is there.”
“In contrast, a character with high Intelligence and low Wisdom is probably oblivious but clever. The character might not spot the clean section of wall but, if asked about it, could immediately deduce why it’s clean.”
“Wisdom checks allow characters to perceive what is around them, while Intelligence checks answer why things are that way.”
The italics, as always, are mine.
So, that’s great and all, because now you know just what they mean by Intelligence and Wisdom, and how Perception and Investigation are different. Granted, there’s that little bit in the PHB about Investigation involving “looking around for clues”, but we’re going to conveniently ignore that, because it doesn’t fit with the rest of what’s being said. Maybe it means that you can look around for clues all you want, but you won’t find any without good Perception… yeah, that must be it.
What the rulebooks haven’t told you, either as a player reading the PHB and trying to choose the best skills for a character, or as a DM reading the DMG and trying to figure out how Perception and Investigation are different, is how to actually use the skills in the game. Let’s face it, conceptual grasp of how the game designers intended for the skills to differ is pointless if you can’t actually put the concept into practice. And that’s why we’re here today. We’re going to put Perception and Investigation into practice, and we’re going to do it in a way that makes both skills important, and we’re going to do it in a way that is centered on actually running D&D games instead of just thinking about them.
Player Stupid vs. Character Stupid
I feel strongly about the issue of separating player minds from character minds, which means that we need to deal with that right now, before we get any further into this discussion. Not only is it something that I get worked up over, it’s also something that is going to be really important when we start talking about how Perception and Investigation really work.
If you haven’t read my DM Credo, go up to the Getting Personal section of this website. If you skip over the stories from my youth and most of my sanctimonious profundities about how I run my games, and instead scroll immediately all the way down to the bottom, you’ll find this:
I will never intentionally put a player in the position of having to separate his or her own knowledge from that of a character.
What does that mean? It means that I purely hate it when DM’s try to tell their players that, while the player might know something, their character does not know that thing, and that the player is then expected to “play stupid” and make bad player decisions because of the character’s lack of knowledge. Many of those DM’s even have the temerity to call this “good roleplaying”. News flash: it isn’t good roleplaying. It’s just forcing players to compromise their judgement as real and sentient individuals, in order to maintain some ridiculous fiction in which they have to pretend that they don’t know things that they actually do know, or else be guilty of “bad roleplaying”. The thing that makes this doubly ludicrous is that with just a little extra thought and care on the part of the DM, this never even has to happen. There’s probably a whole other article waiting to be written on this topic, but this isn’t that article. Right now we only care about Perception and Investigation. Deep breath.
So, when we get into how Perception and Investigation are different, we’re going to do it in such a way as to let players play the best they can. Even better, the ways in which they’ll be able to use those checks will be perfectly reasonable based on the way that actual people would behave in the sort of situations that would have to do with Perception and Investigation. And, best of all, Perception and Investigation will both be important and useful, but in different and complementary ways, and not just the same thing with a different name.
Getting It Right
I’m going to do this with a lot of example dialogues, because I think that’ll be the best way to show how players controlling characters with different Perception and Investigation skills would actually interact in common D&D situations. But first, two caveats.
A Word About Passives
Everybody knows that there’s Passive Perception. It even has a special place to write it down on the 5E character sheet. Passive Perception is just the stuff your character notices without specifically trying, so the DM can provide a certain level of information whenever a character enters an area. There might be obvious traps, secret doors, faint inscriptions, or whatever else. The higher the Passive Perception, the more stuff the character notices without having to specifically look around for it.
But, you can use Perception as an active check as well. When the character is going to go and specifically look at that wooden chest, the DM might call for a Perception check to be rolled, and determine based on that if things like false bottoms, hidden buttons, or invisible objects are found on closer inspection. Both of these are completely reasonable ways to use Perception, and they happen all the time, no problem.
There is no Passive Investigation, and there can never be any Passive Investigation. If you want Investigation to work at all, it needs to always be a rolled check. A character who wants to use the Investigation skill needs to declare what particular thing will be investigated, otherwise the whole system falls apart.
The ultimate reason for this is that the Investigation skill is used when a character is going to carefully examine a situation and think critically in order to figure out important facts about that situation. You can’t just sort of wander around deducing things, because that’s not how reasoning works. Your brain just doesn’t function that way; you need to have facts before you can start working on conclusions.
If you’re thinking you can actually go around passively reasoning things out, I’m willing to bet that you’re not accounting for the fact that you’re observing things first, and then reasoning based on the observations. And observing things is Perception, and observing things as you wander about is Passive Perception. There is no Passive Investigation, because you can’t make any deductions without facts and evidence, and you can’t obtain facts and evidence (at least in D&D) by wandering around and being intelligent.
What the DM Is Really Saying
When you read through the dialogues I’m going to give, I want you to imagine the characters as real people standing around in an actual location and conversing about what’s going on in that location. I’m writing the dialogues this way because I think it is easier and clearer to think about characters seeing things, and characters hearing things, and characters examining things, and so on, rather than trying to combine player-level thinking and character-level thinking.
Remember, though, that when we’re talking about an actual D&D session, with players sitting around a table (or around the Internet, if you do that kind of thing), all of the information about what the characters see and hear is going to come out of the mouth of the DM. Here’s how these sort of dialogues would actually run in table talk:
DM: [party entering a room, Polly’s passive Perception is 15] “You have come into a abandoned storeroom in the deepest part of the ancient mines, with thick dust and cobwebs that cover everything. Polly, you notice a section of wall that looks much cleaner than the others.”
Polly Perception: “OK, that looks kind of suspicious.”
Everyone Else in the Party: “Yeah, really suspicious.”
Isaac Investigation: “I go over to the wall and give it a good look over.”
DM: “You start examining the suspicious clean wall. Give me an Investigation check.”
That’s what’s actually being said around the table, but I think it would be confusing to interject a lot of “DM Says:” into the dialogues, so I’m removing that step in order to avoid confusion. All Perception check results are going straight into the characters’ brains, just as if they were actually there making the observations, and that’s how they’re going to talk in the dialogues.
Especially remember, though, that when we’re talking about players at a D&D session, the results of the Investigation checks will also be coming out of the mouth of the DM. Players will be able to make decisions and plans based on that information, but the players won’t be the ones actually articulating the deductions that their characters made, any more than the players will be the ones narrating what their characters saw.
The DM is the window into the world, and that’s how all of the information from Perception and Investigation checks will be conveyed to the players, even if it seems like that’s not how it’s working in the dialogues. It might help you to imagine the DM narrating information in between the different characters talking, because that’s how they’re actually getting the facts to put into their sentences.
What’s more, we don’t want to tell the players to turn off their brains and not try to make deductions from the information that they get. People’s brains work that way, and you can’t get them to stop. Remember this?
Moving onward, then.
Perception and the Information Gap
Perception is about being observant, and when you’re observant, you notice things. Characters with high Perception (passive or rolled) are going to take in details of environments, objects, or even monsters and NPC’s. And those details are going to become part of the knowledge of not just the characters, but of the players of those characters; remember, we absolutely don’t want the players to have to pretend to not know something that they (the players) know, but that their characters don’t know.
“The character might spot that one section of a wall is clean and dusty compared to the others, but he or she wouldn’t necessarily make the deduction that a secret door is there.”
That’s one of the most idiotic things that the PHB has to say, and there are some real whoppers in there. Why is this statement so inane? Because even if the character wouldn’t make the deduction about a secret door, the player would absolutely make that deduction. You can’t stop the player from making the deduction; they just sort of do it automatically as soon as you tell them about the clean section of wall.
This seems like a really big problem, because of what use is a skill like Investigation, which is all about characters making deductions, if the players are going to be making deductions on their own? This is where we have to be very clear that players are not characters. Characters don’t have normal brains, because brains are very complicated and we need something much less complicated for D&D. We need small numbers that are easy to add and subtract, or we get into trouble. That’s why we break up a character’s entire mind into just two ability scores (with a third to cover personality). Think back on this:
“A character with high Wisdom but low Intelligence is aware of the surroundings but is bad at interpreting what things mean.”
“In contrast, a character with high Intelligence and low Wisdom is probably oblivious but clever.”
So there’s a type of character who is observant, but also kind of dumb. And there’s a type of character who’s smart, but also kind of spacey. And, of course, there are all points between, but for the sake of examples, I’m going to be sticking with the end points.
Demonstration by Dialogues
This is where we’re going to look at some character-to-character interactions, so remember as we go through that the participants in the dialogues are meant to be characters, not players. Still, bear in mind that the players are controlling their characters, and that I fully intend for the players to know just as much as their characters, and to be using that knowledge with their player-brains, no matter what their character-brain-stats or character-skill-stats might be. Off we go.
The Ideal Case: How It Ought to Be Done
This is the best-case scenario, and it happens when you have some characters with good Perception, and also at least one character with good Investigation. If you were waiting for me to actually state how I think the Perception-and-Investigation relationship should work, here it is:
Polly Perception: [passive Perception entering the ancient storeroom] “Hey, guys, there’s this piece of wall here that looks really clean. Isaac, come check this out!”
Isaac Investigation: [rolls Investigation on the wall] “Yeah, this totally looks like a secret door. The hinges must be on the other side, unless it slides up and down. No handles, so there should be a mechanism of some kind to get it open. Everyone, take a look around.”
Polly Perception: [rolls Perception on the area around the door] “Look, here’s a mysterious slot next to the clean wall. Isaac, what do you think?”
Isaac Investigation: [rolls Investigation on the slot] “I’m thinking this is where we can get at that mechanism and spring the door open. Who’s got the thieves’ tools?”
Roger Rogue: “Thieves’ tools? Everybody stand back, I’m on the job!”
That’s how you work it, DM’s. Maybe Isaac Investigation can’t notice things on his own, but as long as there’s at least one Polly Perception in the group (and there’s always at least one; Wisdom is almost never a dump stat, and Perception is a popular skill to take), it doesn’t matter. The observant characters direct the deductive character’s attention to whatever they find, and then the deductive character figures out how it works, or what it means, or how to solve the problem.
That doesn’t mean that the players have to pretend that they don’t know that there’s probably a secret door or something when they see that suspiciously clean wall. The players are going to start deducing that in their player-brains as soon as the DM says that the wall is clean. But, it doesn’t matter, because until the Investigation check is made, neither the characters nor the players truly know how to handle the situation, because that information is locked up in the DM’s brain until it’s time for it to be shared.
Second Case: Playing It Without Investigation
In this second dialogue, we’re going to see how a situation might play out if there’s nobody with Investigation in the party. Remember, Investigation is just an Intelligence check with a modifier, so anyone with decent Intelligence can try to figure out how things work and what things mean even without Investigation proficiency. But, maybe you have a party where you have no Intelligence-based spellcasters, and the fact is that Intelligence is a useless stat unless it’s your spellcasting stat or you’re doing Investigation. So, it’s possible that this sort of thing could happen:
Polly Perception: [passive Perception entering a room] “Look at this over here. This piece of wall looks really clean, and there are some really obvious deep scratch marks on the floor in front of it. I bet it’s a secret door, because it looks just like they always look.”
Druid Dave: “Anyone have an idea how to open it? I sure don’t. I wish we had someone smart to figure this stuff out.”
Molly Muscle: “Ah, screw it. Everyone stand back, I’m going to just rip this thing out of the wall.”
Does Molly’s plan work? Maybe, but it depends on whether there’s actually a secret door there, and there might not be. Yeah, Polly Perception saw some very clear indications that there’s a secret door, and now all of the players have done some deducing in their player-brains that there might be a secret door there.
But, there might not be a secret door at all. And if there is, maybe it’s the kind that Molly Muscle can just break open, but maybe it isn’t. Without the Investigation aspect, both the players and the characters are just guessing as to what they ought to do next. And, if you think about it, that’s exactly what people would do in a situation where they find something but don’t know how it works: they just sort of guess as to what to try next. Maybe it’ll work, and maybe it won’t. Something like this could even happen:
Polly Perception: [passive Perception entering a room] “Look at this… there’s a hole in this wall.” [rolls Perception on the hole] “Sure looks deep and dark in there. I wonder what it’s for…”
Druid Dave: “I bet it’s to let lethal gas, or a flood of water, or acid or something through into the room to kill us.”
Roger Rogue: “I think there’s probably some treasure or something inside there.”
Molly Muscle: “Got to be a switch or a lever or something in there, to open up a secret room or something.”
Reckless Roxanne: “Deep dark hole in the wall? Sounds like someone ought to just stick their hand and entire arm inside there and fish around. I’m going to do that right now!”
Now Polly has found something pretty non-specific, unlike the clean wall with scratches that had all the earmarks of a secret door. There’s just a mysterious hole in the wall, and without anyone to investigate it, everyone has their favorite guess as to what it’s for and what they should do about it. And that also goes for both characters and players, because the players are going to form a guess once they hear about the hole, and that’s fine. One of them might even be correct, and it’s even possible that they’ll do the right thing through sheer dumb luck.
Another possibility is that they’ll do the right thing based on player deduction. What I mean by that is that even when their characters don’t have the Investigation skill, which allows examination of evidence and deduction as a game mechanic, the players themselves do have the capability to examine evidence and make deductions. What this means is that eventually a player will make a deduction that none of the characters could possibly make, and the party will act on that deduction. This seems very problematic: if the characters couldn’t come up with the solution, how can we allow the players to do it? Head on back to Getting Personal, and find this:
I will recognize that the ability scores of characters have no bearing on the abilities of players. I will never require a player to “be stupid” at the table just because a character has low stats. I will never allow a player to claim a “smart character” as justification to solve riddles or puzzles just by rolling dice.
What does all of that mean? It means that the player with the barbarian with the Intelligence dump stat doesn’t have to sit quietly while the party solves the kind of problem that smart people solve. Players aren’t characters, and they can’t be limited by the constraints that bind their characters, nor should they be. If you still think allowing smart players with stupid characters to examine, and solve, and deduce is a bad thing to do, think about this one: what if a particular player was really clumsy? I’m talking about tripping over one’s own feet, can’t walk and chew gum at the same time clumsy. Would it make any sense at all for me to penalize the Dexterity stat for that player’s character just because the player was a klutz? Take the flip side, too. If I had a player whose character had a low Charisma stat, should I give the player a hard time for having good personal interactions with the other players?
Obviously both of those cases are ridiculous. Players shouldn’t be bound by their characters’ statistics, and that goes for both physical and mental stats. It also goes for proficiency, for that matter. Requiring players to exercise bad judgement and ignore the conclusions and deductions that they reach themselves, just because their characters have low Intelligence, is lousy DMing. It forces players to limit their participation in the game, just because their characters are the “wrong type” for a particular game situation. That means they’re just sitting around while the other players have a good time dealing with something, and that’s not at all enjoyable. Decreasing the enjoyment the players get from the game has to be done only for really good reasons. This isn’t one of those reasons.
Are there times when a character’s stats will get in the way of a player’s plans? Sure. If Charisma is your character’s dump stat, you shouldn’t be planning to do a lot of smooth-talking of NPC’s, no matter how eloquently you can phrase things yourself. But that’s not what we’re talking about here. Characters with low Intelligence will not be getting useful information from rolling Investigation checks, but that doesn’t mean that the players of those characters need to shut down their brains. Like it or not, the DM can’t stop the players from thinking, and smart DM’s won’t even try.
If you feel like dumb characters benefiting from smart players is somehow cheating or metagaming or whatever your latest dirty word is, just get over it. Human beings think, and you can’t stop that, and you shouldn’t try to constrain it either.
Player deduction will happen. Just as long as the DM realizes that no information needs to be supplied based on player questions and conjecture, it’s fine. If the party doesn’t have someone who can do Investigation, the DM doesn’t have to tell them what observed evidence means, or how to manage a trap, or how to open that secret door, or whatever. Let the players talk amongst themselves and decide whatever they decide. It does nobody any harm to let them speculate, and even to let them act on their speculations. It’s just a more complicated version of confused people guessing what will work the best, because without direct DM input based on character attributes, both the characters and the players are just casting about for the best thing to try.
Whatever happens, the second case ends with either the party figuring out the right thing to do without the Investigation skill, or else failing to figure it out. There might be danger involved with trying the wrong thing, and not solving the problem might be obstructive to their progress through the adventure, but ultimately either they’ll do the right thing and move onward, or they won’t do the right thing and get killed or stuck. As the DM, you just have to let this one flow.
Third Case: Complex Observations and No Investigation
There’s a third case as well, and that’s when a lack of Investigation brings the whole endeavor to a halt. Think about this:
Polly Perception: [passive Perception entering a room] “Take a look at this ancient and mysterious altar. It has all of these strange runes around it. Weird.” [rolls Perception on the altar] “And all of the runes have tiny holes in the middle. Really weird.” [rolls Perception on the floor near the altar] “There are some scratches here, but they’re just kind of swirly, except for the ones that are scribbly. Extremely weird.”
Druid Dave: “Sorry, guys, I got nothing here.”
Roger Rogue: “I could start in with the thieves’ tools… but where to start? There have to be a couple of dozen of those holes.”
Molly Muscle: “Looks to heavy to shove or lift, and that’s basically all I can do. Maybe I could hit it with something blunt? Unless something sharp would be better…”
Reckless Roxanne: “If I could only find a way to hurt myself with this thing… maybe I could trip over someone’s foot and hit my head on that sharp corner?”
If you have a really intricate set of details, your players are going to bog down almost immediately because there’s no obvious answer, and also no ready-to-go deductions forming in their player-brains. This is when the players start trying to throw their best statistics at the problem, but it’s all very hit-or-miss. The characters are mystified, and the players are also mystified. Something that’s interesting about this type of situation is that the complexity might not have anything to do with the solution, and it’s entirely possible that all that altar really needs is a good shove from Molly Muscle. The overall point here is that there can be things in a D&D game that really cry out for someone with Investigation, or at least decent Intelligence, and that creates a bit of an awkward situation when there isn’t anyone like that around.
No Investigation? No Problem. (Sort Of.)
This section is mostly for you DM’s reading this article, because figuring out how to handle tough situations in the game is ultimately the DM’s job. If you have a situation where some Investigation (or at least Intelligence) is needed to figure out something complex, but you don’t have that capability in your party, one way to handle it is just to let the characters try whatever they can think of, until either something works, or they give up and go do something else, or they set off a trap and get killed. Essentially this is the same shooting-in-the-dark as in the mysterious hole example. Even if the observations are very complex, as in the altar example, it’s the same thing; the difference is only superficial, because the players don’t automatically and swiftly develop theories and deductions. Instead, the guessing is just guessing, instead of guessing that attempts to be justified by conjecture.
If you’re going to go this route, letting the players try to come up with a solution on their own without an Investigation check, be very flexible. If the players try the right thing but don’t quite make the DC (as in rolling a 12 on a DC 15), let them succeed anyway. If they come up with a solution that’s pretty close to the right one, good enough. If they develop a really interesting and creative solution that doesn’t solve the problem, you might even consider changing the “official solution” so that the creative solution is the right one. The overall point here is to recognize that if they guess almost-right, but not quite close enough (think about that missed DC), and they fail, they probably won’t try that method again, and the fact that they hit on the right way to handle the problem will never matter.
Another way to handle the Investigation dilemma is just to not include elements in your game that require a skill that the party doesn’t have, but I think that’s pretty much a cop-out. It’s like not having monsters who resist non-magical damage, just because your characters don’t have magical weapons. Give the players some credit for being smart and creative, and let them have opportunities to show that off. Removing challenges makes things very boring, and it’s also a sure-fire way to get your players into that we-can’t-lose attitude, that soon becomes that what-we-do-doesn’t-matter feeling, that then destroys your game. Don’t kill your game over some complicated treasure chests.
Something that you can and should do is make sure that the players understand that not every puzzle can be solved (at least not by them, or not by them right now), and also make sure that they understand that not every puzzle needs to be solved. If the players are going in with that completionist mindset, and they feel like they have to explore every room and fight every enemy and solve every puzzle, they should probably be gently guided into realizing that you, the DM, don’t think that’s how it works. Or you can just flat-out tell them that they should not expect a 100% success rate, because that’s a ridiculous performance standard for anything, D&D included. Depends on your style, I guess.
Watching Out for Sherlock Holmes
There is one final case that we need to talk about in order to round out this article, and that is what happens when you have Sherlock Holmes in your party. I suppose it’s possible that someone reading this might not have ever seen Sherlock on BBC, or Elementary on CBS, or any of the (stupid) movies, or the old Public Television series, or listened to the really old-school radio dramas with Basil Rathbone, or even actually read the books and stories by Sir Arthur Conan Doyle.
If that’s you, then the thing that you need to know about the fictional character Sherlock Holmes is that he is a wildly successful late 19th-century British detective who solves the most difficult and exotic mysteries, with flair and panache and a certain adorable arrogance. He has vast knowledge about all things to do with crime, but that is secondary to the fact that he is capable of making the most thorough imaginable examination of the evidence, and then drawing the most complex and ingenious deductions from his observations.
In other words, and to match the terms we’re working with in D&D, Sherlock Holmes has high Perception and high Investigation at the same time. He notices everything, and then he uses his observations to figure out what everything means. You could have a character like this, probably a rogue with high Intelligence, proficiency in Investigation, decent Wisdom, and double-proficiency in Perception from that Expertise class ability rogues get.
The problem for a DM with this kind of character is that it short-circuits the party involvement in figuring things out. When we had Polly Perception working together with Isaac Investigation, there were two characters playing off of each other’s strengths, and that’s a really good way for things to work. There are even some side benefits, like that it takes up some time going back and forth, which makes it easier to make the evidence and the conclusions match up in the players’ minds. It also allows the players who aren’t directly involved in the observing-and-deducing to come up with their own unspoken personal guesses in their own personal minds, which gives them a little extra interest when they find out whether their idea was right or not. But, when you have a Sherlock in the party, all of that goes away:
Sherlock Holmes: [passive Perception entering a room] “I observe that there are a series of holes bored into the wall on the left side of the room.” [roll Perception on the holes, and then roll Investigation based on the Perception] “There are no noticeable scratch marks here, which indicates that these holes are not meant to fire arrows. Likewise, I observe no mildew that would indicate that water or other liquids are meant to pass through the holes. Based on a faint smell of sulfur, I conclude that these holes are meant to fill this room with a suffocating and toxic gas.” [stop for a breath] “I noticed a pressure plate here in the floor as we entered.” [roll Investigation on the pressure plate] “If someone places a wedge or pointed tool here under the edge of the plate, it will stop the trap from triggering and flooding the room with lethal fumes.”
Dr. Watson: “Astonishing, old man, astonishing!”
This degree of show-stealing would quickly become tiresome for everyone involved, but that’s not the worst thing about it. The worst part is that the character isn’t actually doing the observing and deducing, and neither is the player, either of which would actually be pretty impressive and entertaining. That’s why there are four novels, five books of short stories, and a large handful of television shows and movies and even radio shows, which are all basically about Sherlock Holmes solving mysteries this way. In D&D, it doesn’t work that way, because all of the observations and deductions are pretty much being managed by the DM, who is the one at the table with all of that information. The only one with all of that information, in fact.
So when you make a Perception check, the DM tells you what you see. And when you make an Investigation check, the DM tells you what you discovered. And when you have one character doing both of those types of checks, the DM basically sits there and expounds upon the mysteries of the dungeon, with possibly some pauses so the Sherlock Holmes player can roll some dice. And while this is going on, all the other people at the table are basically doing nothing except for waiting for Sherlock and the DM to tell them what they need to do in order to handle the situation that Sherlock and the DM have figured out for them.
Except Sherlock hasn’t really done anything to figure anything out. Sherlock just has character stats and abilities and skills and class features that ruthlessly shanghai the DM into revealing all of the details and solutions. So now you have the DM just telling the players what the characters need to do in order to fix this problem, solve that puzzle, disarm the trap, open the door, or whatever. At this point I hope everyone realizes that creating a situation where the DM just tells the players what to do, and then they do it, is a really bad idea. Especially if it happens over and over again, every time there are observations to make and a conclusion to draw.
So, as a DM, how do you dodge this particular bullet? I have no idea, except to house-rule the bullet out of existence. Making up house rules to fix game-breaking situations that technically fall within the rules-as-written is always kind of a lousy thing to do, but this is one of the times when you probably need to do it anyway. Remember that one of the reasons we’re playing D&D is for entertainment: that goes for DM’s and players both, by the way, and listening to the DM explain all of the things that the Sherlock character sees and knows is not entertaining. There’s no teamwork, no figuring out a problem, no using individual skill towards a collective accomplishment. It’s just the DM saying, “so, what Sherlock sees is [fill in a detailed description of the area], and he figures out that [reveal all of the deductions and conclusions and secrets and surprises in the area]. What you need to do based on all of that is [explain how the Investigation results have to be used]. So… what do you do next?”
And that’s crap D&D, folks. If you’re a player and you think that a Sherlock Holmes character would be cool to create and play, you’re wrong. If you’re a DM and you have a player who wants to make a Sherlock Holmes character who can both observe minutely and deduce brilliantly, tell them that they can’t, and tell them why. Make sure that they really understand how awful the consequences of having both Perception and Investigation would be. It’s really that simple: characters can either be good at Perception, or they can be good at Investigation, but it’s a bad move to allow any single character to be good at both.
A Summary, and a Closing
Perception and Investigation are easy to use together in your games. It doesn’t really matter what conceptual reasoning you like the best to explain why they are different; you need to be able use the skills in the game. That’s where the rulebooks fall short: they explain all about what Perception is, and what Investigation is, and how you can tell them apart, but they never just come out and say how they can be used together in a way that translates into gameplay mechanics.
The way they fit together is very simple. Characters with good Perception notice things, which means that the DM describes physical attributes of the local area for everyone at the table to hear. At this point, players are generally going to form some thoughts about what might be the reasons for those facts, like beginning to suspect a secret door when the DM describes scratch marks and clean walls. They might even start to think of some things to try, based on those suspicions.
None of that is a problem for the game, because you’ll need the character who noticed the interesting features to point them out to a character with good Investigation, because that’s who can really examine the evidence and figure out what it all means, at which point the DM can narrate the deductions and the details. Without someone to do the investigation, everyone pretty much ends up guessing what to do, and that’s also fine, because that’s what people do when they see something that looks important but that they don’t understand. They fiddle with it, and hope for the best.
The best part is that the players don’t have to pretend that they aren’t thinking human beings. People try to take information and figure out what it means, and that’s just the way our brains work. That’s also pretty much the way a D&D character’s brain would work, actually. Formulating explanations for the things we see and hear happens automatically, and there’s no way to stop it.
But we don’t need to stop it. Maybe in the Investigation step, some of those explanations will be verified by a character who’s good at deducing, and reasoning, and figuring out what things mean. Maybe the investigation will come up with something unexpected. Maybe there won’t actually be an investigation, and everyone will just sort of blunder around until something happens. Any of these are acceptable outcomes.
So throw the conceptual nonsense out the nearest window. Perception is for gathering evidence, and Investigation is for figuring out what the evidence means and what to do about it. If you’re the DM, dole out your Perception information first, and then let the players figure out what needs a closer look, or what needs some Investigation. If you play a character with high Perception, take charge of looking for things that seem important, and then call in the character with Investigation to try to figure out what it all means. And, if you play a character with high Investigation, remember that other players are going to be looking at you to figure out what to do next. The DM will provide the information, but you might be the one who has to turn that information into a proposal for action, because you’re the one that the DM is going to be looking at when the deductions are explained.
And that wraps it up. Everyone probably already knows what Perception is all about, and everyone has their own pet explanation for what Investigation means, but you now know how to actually use both of them in your games. And being able to have functional mechanics that you can actually use to drive a game beats hell out of properly conceptualizing abstractions. Every single time.