In a hypothetical situation, I want to destroy a castle's walls. To do so I came up with the idea to build a bomb a la Saruman in LOTR. Perhaps my character would have to dig around for records on bomb-making, search for the ingredients, and finally craft this device, as par the course for an RPG. However in retrospect my character might not even know such a thing exists in the first place. Certainly Theoden did not realize that his castle could be overcome by such a device, and made no precautions against it in LOTR. Thus, would undertaking this plan be considered metagaming because it came from knowledge that I knew, outside the game?
In this situation: if you have to ask, it's almost certainly meta-gaming.
This sounds flippant, but it is not. This could also be construed to apply to any meta-gaming question, but I do not intend it that way, I intend it for the narrow class of, "Is it meta-gaming to build X?" and closely related questions.
Meta-gaming, very tersely defined, is the inappropriate application of player knowledge to guide character actions.
In this case, the player knowledge is somewhere on the spectrum of, "There are chemicals that can be made to explode," and "the chemical formula of TNT is and can be made by the following process; see footnotes for procedures to avoid blowing up self." In other words, you the player know bombs exist. You might know a little or a lot about how to build them.
The desired character action is, "The character builds a functional bomb of some sort, by some process."
The thing that makes this sound meta-gaming is that there is no obvious and appropriate link between the character knowledge and the character action only between the player knowledge and the character action.
Conceivably there could be. We don't know much about this game setting. It could be a post-apocalyptic earth with legends of explosives. It could be the Guardians of the Flame universe, which was straight-up fantasy where conventional explosives worked. It could be some homebrew fantasy where dwarven miners are rumored to use such things. On the other hand, it could be homebrew fantasy where explosives just don't work by divine/GM fiat, period.
What causes me to think that this is meta-gaming, and what causes me to formulate the answer as "If you have to ask, it's probably meta-gaming," is that by the phrasing of your question you don't know, either. As you say:
However in retrospect my character might not even know such a thing exists in the first place.
If you're not sure where it is your character is getting an idea, it's probably coming from you the player, and not the character's interaction with the game world. That makes it meta-gaming in my book.
As an addendum, some level of meta-gaming is almost unavoidable. We as players have a rich and detailed first-hand knowledge of exactly one world (the real world) and probably shaky knowledges of other fictional worlds.
It's almost unavoidable to ask questions like, "Hey, does this world have gunpowder?" or "Does this world have xorns I could capture to eat the castle walls?" purely in order to efficiently sharpen our knowledge the game world we're playing in. But you can avoid going very far down those roads by asking your GM and then abiding by his or her answer.
Is it metagaming?
In an RPG context, metagaming "is an "out of character" action where a player's character makes use of knowledge that the player is aware of but that the character is not meant to be aware of."
You know about explosives: I will hazard a guess that you couldn't make a bomb without finding out more than "bombs exist". If you character knows about explosives then this having your character do the same type of research you would do is not metagaming. If your character doesn't know about explosives then it is metagaming.
Of course, at some point in history no-one knew about explosives. The first bombs were used in 1221 but gunpowder had been known and used since the 10th century, 200-300 years earlier. Clearly, knowledge of gunpowder does not mean knowledge of bombs - in logical terms, gunpowder is a necessary but not sufficient precondition for bombs.
The only way to tell if this is metagaming is to ask your DM what the in-world knowledge of bombs is.
Is metagaming bad?
The unspoken assumption in your question is that metagaming is, in some way a bad thing.
All games (not just RPGs) involve metagaming. When the coach of a football team decides her strategies and line-up based on who Saturday's opposition is, she is metagaming - this is knowledge that exists outside the rules of the game. When a player in an RPG decides to cut and run based on their character's hp total, he is metagaming.
Metagaming is built into your game by the mere fact that you are you and your character exists as a pile of numbers on your sheet and in your group's collective imagination. In other words, your character is also you.
So, why is metagaming bad? Or, with more nuance, which types of metagaming are bad and why?
I don't have an answer for you: that's up to you and your group. But please, just think about the question ...
It depends on your setting and your DM.
While lots of ink has been spilled about whether metagaming is good or bad or inevitable, the crux of your question is, "would my character know about bombs in-universe?"
The answer to that question is maybe.
The DMG supports the inclusion of bombs in a campaign. DMG 267 has a long section on bombs, dynamite, and even grenades, detailing their cost, damage, and other effects. Therefore, the developers have considered the presence of explosives in their game, and it's plausible for such things to be knowable ingame.
Of course, that section of the DMG also describes things like alien technology and ray guns, too. It is up to the discretion of the DM to include such items in the campaign. Therefore, only your DM can tell you if your character would know about bombs.
Think outside the box
While bombs as we understand them might not exist in a D&D fantasy world, your character would sure know about explosions, because they are everywhere in D&D. Fireballs and Glyphs of Warding are basically explosions, and the DMG describes a few magic items that can explode.
Therefore, if your character wants to go about making a huge explosive, he might not go the real-world, chemical route. Maybe he could look up some way to make a one-time use magic item that detonates a particular powerful fireball, or even a custom spell that's able to cause a wall to collapse (the Stone to Mud spell, perhaps?). In this way, your character can successfully research a way to take down this wall using 100% ingame knowledge.
Again, however, if/how this works is up to your DM to decide.
The question is:
- Does your character know explosives exist?
- Does your character know which substances to mix in what way to create an explosive?
- Does your character know how to safely handle these substances in order to make them explode at the right moment?
Depending on your setting and character background, the answers might be:
- No, there is no way your character could know that, so you can't do it.
- Yes, your character would definitely know this, so you can do it.
- Your character might or might not know. Do an Intelligence check to find out. Keep in mind that if you need an Intelligence check for the 2nd or 3rd, the DM might not tell you if you succeeded in your roll, so you might not get the results you expected.
It's up to the DM to decide the answer to each of these questions.
If your character has no idea that such a thing is possible, yes. Depending on the characters knowledge and the setting, I might or might not allow it.
I would argue that there are certain technological advances required in the civilization where this bomb is to be built before you can even consider doing it. At the very minimum there needs to be black powder or something similar. You would need to be able to create or find the required ingredients. You would need specialized tools and equipment to produce it in large enough quantities.
If it does exist, that would be reflected in the world in some way. Civilizations are shaped by massive leaps of technology like gunpowder. One option would be that perhaps only a certain civilization knows about it and guards the knowledge, or it's dangerous enough to create/handle so that only desperate fools use it.
If it doesn't exist, it's not really in the scope of a DnD adventure to create it from scratch. In theory I guess your character could dedicate decades inventing it, weaponizing it, and then engineer an explosive device, but I doubt that's what you have in mind.
If in that world, there is magic or gunpowder that can be used to make explosions,
why wouldn't a PC try to imitate that?
If anything like that is known to exist in-world the I would rule that it is not meta-gaming to try to make something similar. It would take time, resources, and ability checks but as a DM I would give the character a chance.
"Is it meta-gaming?" depends on two thing:
- The world (is concept known to exist?
- The character (Would your character know if it exists, and if not, would the character be smart enough to think of new concept like that? In the second case, a very high Intelligence check would be called for (Using Ability Scores, PHB, Chapter 7).
No, it is not metagaming.
Contrary to other people's opinions here, I'm going to have to go with a pretty firm no.
What happened here seems to be more a case of a shortcut rather than actual metagaming. You have tremendous knowledge of your world and comparatively little of the campaign world you're playing in. Your character on the other hand knows nothing of our world and a lot about the campaign world.
However, there are places where your knowledge overlaps. Your character would know that explosions exist. After all, they're an adventurer and have been exposed to things like fireballs (which make things explode), Alchemist's Fire (which makes things explode), Glyphs of Warding (Which make things explode), swamp gas (which explodes), lamp oil (which can explode but rarely does) and so on.
In a relatively civil environment, it's surprisingly easy to make something explode. A typical D&D campaign has a lot of things that can go BOOM under the right circumstances.
Saw mill: if it gets too dusty: BOOM.
Flour mill: not careful and someone lights a match? KABOOM.
Swamp: Swamp gas has a tendency to catch fire and/or explode.
Mines have a tendency to collect gas that, you guessed it, explodes.
- D&D has the Alchemy toolkit which lets you do basic chemistry like combining an acid with a base to produce hydrogen gas which explodes.
Hell, get a big bottle of dwarven rotgut, add a fuse of some description and you've got everyone's favorite home explosive: the molotov cocktail.
Long story short, there are a LOT of ways that things can explode and adventurers are prone to needing ways of killings things, so they're very likely to have at least heard of explosions. All that's left to do is figure out how to build one with the means you have.
What happened here?
Some might say you'd be metagaming. What I'd say is that your character went over the options in their head and concluded that Perhaps an explosion is what it takes to destroy the castle wall. It sure is quicker than the traditional method. Let's do some research.
Don't forget that one of the ways of taking down a castle wall in medieval siege warfare (upon which fantasy warfare is loosely based) was digging a tunnel underneath the wall, loading it with flammable goods (Pitch, wood, oil, occasionally pig fat or even pig carcasses) and setting it on fire. Surely some sort of alchemical solution can do the same thing, but faster?
Give this problem to a smart or practical character and you're bound to end up with explosives of some sort as a solution. Sure, maybe not something as stable as gunpowder or TNT but stable explosives are for suckers.
As per Robotnik's suggestion, it should be noted that all of the above only works for a character with a reasonably cosmopolitan background. A druid hermit who's lived in the woods all their life isn't going to come up with any of this (unless he has previously weaponized swamp gas).
Yes, it would be meta-gaming, but you have to ask yourself 2 questions:
- Why is meta-gaming bad?
- Is it possible to even play the game without meta-gaming in any way?
Ultimately it depends on your group composition, attitude, and DM whether such things are acceptable or not.