What does the Rules Aren't Physics quote mean?

Question

In the new rules it says:

Rules Aren’t Physics. The rules of the game are meant to provide a fun game experience, not to describe the laws of physics in the worlds of D&D, let alone the real world. Don’t let players argue that a bucket brigade of ordinary people can accelerate a spear to light speed by all using the Ready action to pass the spear to the next person in line. The Ready action facilitates heroic action; it doesn’t define the physical limitations of what can happen in a 6-second combat round.

What is the example meant to illustrate? Is heroic action defined? Is it saying only PC's can ready? Or can ordinary people ready actions? Is it saying they can pass along a spear over a large distance in one round but we should not make assumptions about it going at the speed of light or in fact the spear having been "accelerated" which is a real world term not a dnd one? Or are they saying that you shouldn't allow a spear being passed along with many ready actions, i.e. that you should only allow a reasonable number of such ready actions to work?

(To me the example clarifies very little of what it means that "Rules Aren't Physics".)

Answer 1

The Bucket Brigade is just an example

The objective of the quote is to clarify that you should not approach the rules with a mindset that they should follow real world physics, or even model the game world on a physics level - The first sentence says all you need to know:

Rules Aren’t Physics. The rules of the game are meant to provide a fun game experience, not to describe the laws of physics in the worlds of D&D, let alone the real world.

There are many, many questions of people that fell into that trap on this site, for example:

• How much weight can the standard 50' rope hold?
• Does Mage Hand measure weight as mass or as force?
• Will this arrow fly 4800 ft?
• What does Banishment do to falling momentum?
• Is a fly-by of a ship possible in the astral sea with enough INT
• Shape-Water Vacuum Bomb

the list goes on and on.

All the rest of the paragraph is just providing an example that muddling real world physics and game mechanics leads to weird results, namely the Peasant Railgun (Would the Peasant Railgun work in 5e D&D?). I think they chose it to illustrate this as it is one of the better known examples for this kind of thinking, and on top of that is pretty hilarious.

Answer 2

My answer to the 5e 2014 version of this question is edition/system agnostic and answers this question, so I will reproduce it below. About this new quote from the 2024 rules, I will say that it is not making any particular rule. It isn't telling us how the Ready action works, or how many Ready's you should allow, or how fast things can go. It is guiding the expectations of DMs and players away from assuming the rules are supposed to reliably simulate real world physics, as explained in my reproduced answer. The point is that the DM is responsible for managing those situations where applying the rules strictly and literally allows for physically impossible scenarios. It isn't telling you how to manage these situations, it's just telling you that the rules aren't going to do it for you.

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"D&D is not a physics simulator" is shorthand for a more thoughtful thesis.

As you have observed, "D&D is not a physics simulator" is an oft repeated response to people who seem to bring expectations about the behavior of real-world physics to the table of play. At face value, the saying really is not true, but no one intends this phrase to be taken at face value, it is just shorthand for something more meaningful.

Obviously, D&D does make some attempt to simulate physics. In real life, things fall down due to gravity. If D&D were not making some attempt to simulate this, we would not have rules for flying, falling, and fall damage, but of course, we do. The rules for falling and fall damage are simulating the real world phenomenon of gravity. So what do we really mean when we say this?

The rules of D&D often fall short of meeting our expectations about real world physics.

When we approach the game armed with an expectation that the rules will produce consistency with Newtonian Mechanics, that expectation will not be met because Newton's Laws of Motion are not part of the rules of the game. We're here to play D&D, not crunch numbers using Newton's kinematic equations, so the rules for falling are far more simple than \$\Delta x=v_0t+\frac{1}{2}at^2\$:

When you fall from a great height, you instantly descend up to 500 feet.

Now, the closest thing to a proper reference for this idea found in the game rules comes from the introduction to the Dungeon Master's Guide:

The rules don’t account for every possible situation that might arise during a typical D&D session. For example, a player might want his or her character to hurl a brazier full of hot coals into a monster’s face. How you determine the outcome of this action is up to you.

There is a physics problem and a medical problem associated with hurling burning coals at a person, and one could theoretically try to simulate the resulting injuries reliably if they were armed with sufficient knowledge and experience. But the rules of the game don't try to do that. The rules admit that they cannot account for everything and instruct the DM to make a ruling and move on. It is a natural corollary of this quote from the DMG that the rules will fail to meet your expectations about real world physics. And that is what people mean when they say "D&D is not a physics simulator".

Answer 3

Both Thomas Markov's and Nobody the Hobgoblin's answers are really good but I want to try and expand on what they say.

The way the text says "Don't let players argue that [...]", and "[The Ready action] doesn't define [...]", to me, appears to imply not only that the rules do not cover these scenarios as their answers said, but also that these scenarios are outside the scope of the game entirely, the fact that they can be described under the framework of the rules is a bug, not a feature.

In short: They are not telling you what happens in these scenarios. What they are doing is telling you these scenarios do not happen and giving you, the DM, explicit, ultimate authority to arbitrate scenarios where rules appear to conflict with "common sense", and implying that "common sense" (or "genre expectations") should overrule any such scenarios. They are informing you that that rules arbitrate gameplay but do not define how the world works or where the limits are.

They are saying that rules, especially when interactions between different rules cause emergent behaviors, aren't unbreakable laws of the world; and that it is wrong to assume that something just works "because the rules allow it". Other limitations apply to the game world beyond the rules, and the rules are only there to allow you to interact with the world, not to create a 100% accurate simulation.

In long:

What do they mean by "Rules are not physics"?

The rules of the game are meant to provide a fun game experience, not to describe the laws of physics in the worlds of D&D, let alone the real world.

This part is essentially a disclaimer, stating that rules are an abstraction that won't always accurately reflect what would happen in a given situation. With this they acknowledge that following the rules will sometimes lead to scenarios not compatible with the laws of physics (real or fictional). Reality doesn't actually work in sequential 6-second increments, et cetera.

Don’t let players argue that a bucket brigade of ordinary people can accelerate a spear to light speed by all using the Ready action to pass the spear to the next person in line

This part is describing a specific (in)famous case where following the rules leads to such an scenario. But it starts with "Don't let players argue [that this must happen]", this is explicitly saying "no, this argument is not valid". This is the core of the message they're conveying.

Yeah, according to the rules you can give a guy a spear, have 1.180.285.267 guys stand in line Readying an action to "hand the spear to the guy in front of me when the guy behind me hands it to me" and have it travel 5.901.426.335 feet in 6 seconds, which would mean it's travelling at a whopping ~99,999999983% of the speed of light (if my math is correct, I did ignore decimals). But this does not work because no matter what the rules say, passing an object from a person to the next takes time, a person can't handle an object moving at relativistic speeds, and an object can't be moved FIVE BILLION FEET by very coordinated ONE BILLION people in JUST SIX SECONDS.

The Ready action facilitates heroic action; it doesn’t define the physical limitations of what can happen in a 6-second combat round.

And this final part is telling you what the purpose of the rules is, by using the Ready action as an example. It explicitly says that a rule does not have the authority to decide what happens.

The rules aren't there to tell you what is possible, and using rules as a substitute for "physics" results in scenarios that here are implicitly defined as not supported by the system and you, as a DM, have both the responsibility and authority to prevent these scenarios. The rules are there to tell you how to do the things that are possible, to facilitate the interaction with a world defined by their published material and our collective knowledge of the genre, and not to define the world you're playing in.

So if nothing in the Ready action is explicitly saying "accelerate this spear to 99,999999983% of the speed of light, then you can't accelerate it to 99,999999983% of the speed of light, even if applying the rules in a particular way would allow it to happen.

Answer 4

What does the Rules Aren't Physics quote mean?

The phrase "Rules Aren't Physics" underscores a crucial distinction in RPGs: game mechanics don’t aim to recreate every nuance of real-world physics. Instead, they provide a playable framework for determining outcomes in a way that feels reasonable, without needing exhaustive calculations or bogging down the pace.

Game rules often simplify complex phenomena—similar to how introductory physics ignores friction or air resistance to teach foundational concepts without overwhelming students. These simplifications allow players to focus on storytelling and strategic choices rather than exhaustive simulations of reality. While the rules may not capture every parameter, they offer a balance that keeps the game flowing and engaging.

As a Game Master (GM), this approach invites flexibility: if a particular outcome feels implausible or disrupts the narrative flow, it’s fine (and recommended) to adjust outcomes subtly to preserve immersion and maintain the excitement. Ultimately, the rules are a tool for creating dynamic and immersive stories, not a rigid physics engine, nor should they confine the outcomes. That's why we have GMs!

Good luck!

Answer 5

In particular, it's a reference to the Peasant Railgun.

For historical context, the quote in the question references the "peasant railgun," a gimmick thought up on D&D forums which goes back at least as far back as 2008.

The theory is that you assemble a line of peasants, and each readies an action to pass a spear up the line. Since one combat round takes six seconds, the logical reasoning is that with enough peasants, the spear can be moved so fast that it exceeds the speed of sound, which would make it a deadly projectile.

The logical fallacy is that this assumes the D&D rules are sufficient to simulate the rules of physics in a realistic manner, or that the laws of physics must be applied to D&D. D&D is an abstract set of game rules, not a physics simulation, and players should not assume otherwise. See the question Is there a citation for "D&D is not a physics simulation"? for more discussion.

The peasant railgun is used an example of something absurd, but technically possible by the rules, such that the DM should probably not allow it. The rules were never written with mass-combat in mind, only party-scale heroic adventuring, so they don't make sense at huge scale. Actually, the peasant railgun in particular commits a sort of paradox:

• Accelerating the spear is possible by rules-as-written, but not by the laws of physics
• Dealing massive damage with a fast-moving spear is possible by the laws of physics, but not by the D&D rules

Another example: Suppose I offer a free booklet. Someone appears and demands one million booklets, since they're free, so by my own rules I must comply. In practice, it doesn't work that way!

Answer 6

In some games, Rules are Physics

The physics of a world define what happens when an object is dropped, a person is stabbed, or almost anything that goes on in a world. A game where rules-is-physics is one where the rules of the game is the only thing that determines what happens in a game.

In most board games this is the assumption; the rules define what you can and cannot do, and anything the rules let you do happens.

If in a board game, the rules say you can sell a chicken for 2 gold and buy a chicken for 1 gold and do it as many times as you want, you get as much gold as you want by doing the cycle.

D&D isn't a board game

D&D is primarily a role playing game of improvisation. The players create characters in an imaginary world shared with the DM. The DM describes the world. The players describe what their characters do. The DM describes the result.

The basis of D&D was the DM making up rules on the spot most of the time. Random numbers and dice were used as it was a fun way to keep things unpredictable. When a player wants to check a chest for traps? Well, the DM says "roll 1d6", the DM says "on a 1 or 2 you find a trap, otherwise you miss it".

Those rules got invented by the DM, then written down; having a record of rulings meant the world was more consistent. Over time, the written down rules got polished. What more, the DM would sometimes write rules down before the situation occurred.

Early D&D was gonzo

It had piles of mechanics and optional rules and suggestions for how to resolve a situation. Spells were vague about what they did; a spell that put you to sleep would just say that, and there was no "sleep status" to refer to. They were asleep; what did that mean? Well, guess. Maybe they'd fall down and hit their head and wake up, maybe noise would wake them up, maybe they'd be easy to kill -- but if it was a giant, maybe not.

Complex charts still existed, but honestly people picked and chose which rules to use in their games.

D&D developed towards Rules as Physics

Over time the rules got polished and covered more and more cases. Around the 3e era, there was a tendency for RPGs to create "universal systems". And the d20 system of 3e really tried that. DCs for most actions were codified, from changing an NPCs opinion with diplomacy (take a -20 to do it in a single action) through to jumping distances and the hardness/HP of materials based on inches of thickness.

In practice, it did a mediocre job of it, as game rules trying to act as physics for a world always falls apart. But if you didn't push it, you could feel like it was a complete set of rules for how the world worked.

A popular D&D webcomic, "Order of the Stick", started off as a set of jokes about D&D rules as rules of physics (and that remains a part of the storyline).

4e and reskinning

In the 4e era, reskinning became core. An ability did certain mechanical effects on the world. The flavour text could be ignored or rewritten. The prone condition, when applied to a snake, led to the snake suffering from the same mechanical effects as applied to a titan; the DM was supposed to reinterpret prone to mean some in-world effect that gave the same mechanical effects instead of a gelatenous lying on its side (or whatever). Maybe it was jiggling.

This was a partial break from rules-as-physics; in that the rules happened, and the DM was supposed to improvise the physics, tell a story around the rules.

Modern D&D

In the 5e 2014 and 2024 era, the game rules were made a lot more similar to early AD&D and pre-AD&D rules. We had some remants of the 3e/4e era with defined conditions.

You can see this in a number of spots. The rules for the grid? They were optional. The core rules were actual distances; the grid rules were ways to quickly adjudicate on a grid to simplify things.

In this situation, the rules of D&D are meant to help the DM. The prone condition and attacks that knock something prone are supposed to give the DM advice on what happens when someone is tripped.

If you trip something like a gelatenous cube, even though it doesn't say "immune to prone", the DM is supposed to say "well, knocking it over does X", regardless of what the prone rules say. The action - knocking it over - occurs, but the DM determines the effects.

Similarly, the Ready action exists in order to help the DM decide what happens when someone prepares to do something in response to the situation changing. If the result of the Ready action mechanics makes no sense, the DM is supposed to make it make sense.

The same applies to all of the other 5e rules; the DM runs the world, the rules are meant to help the DM determine what happens. When the rules don't make sense, the DM is supposed to decide what happens instead of blindly following the rules.

Answer 7

What is the example meant to illustrate? Is heroic action defined? Is it saying only PC's can ready? Or can ordinary people ready actions? Is it saying they can pass along a spear over a large distance in one round but we should not make assumptions about it going at the speed of light or in fact the spear having been "accelerated" which is a real world term not a dnd one? Or are they saying that you shouldn't allow a spear being passed along with many ready actions, i.e. that you should only allow a reasonable number of such ready actions to work?

It is not my intent to hurt your feelings, but the purpose of the paragraph is to invite people who react just as you are to calm down and worry less. Allow me to simplify the new rules quote in a way that might make more sense:

Dungeons & Dragons is a game. Just a game. The so-called "rules" presented here serve no purpose other than to provide some basic structure so you and your friends can have fun. But there are days when people really think that everything should be defined, that every rule can be ennumerated, that every moment of gameplay can be circumscribed, or that every issue should be explicable in-universe. Such people have missed the point of Dungeons & Dragons entirely. It's a game and you're meant to have fun. If you're the game master and you're reading this paragraph, remember that 100% of all questions, issues, and discussions can be and should be resolved by you. It's not about having memorized all the rules and the nearly infinite discussions involving them. It's about making a decision in favor of having fun and moving on. What you're reading is not written in stone and not intended to be. These are just guidelines designed to get you started. Nothing more.

The authors of the paragraph you quote are, frankly, mocking the people who worry so much about whether the "rules" are complete or make sense that they'd actually wonder if it's possible to use a quirk in the rules to accelerate a spear to relativistic speeds.

Such people have forgotten why they're playing the game. Or, perhaps, they've simply stopped having fun playing and are now having fun picking apart the obviously and intentionally imperfect rule system. To simplify the paragraph to a single sentence:

Please stop believing the rules in these manuals are absolute or should be.

Answer 8

'Heroic action' means responding to in-game challenges with genre-appropriate choices, not using meta-game exploits

What kind of game is this?

In the introduction to the PHB (5), we are told what kind of game this is:

There’s no winning and losing in the Dungeons & Dragons game—at least, not the way those terms are usually understood. Together, the DM and the players create an exciting story of bold adventurers who confront deadly perils. Sometimes an adventurer might come to a grisly end, torn apart by ferocious monsters or done in by a nefarious villain. Even so, the other adventurers can search for powerful magic to revive their fallen comrade, or the player might choose to create a new character to carry on. The group might fail to complete an adventure successfully, but if everyone had a good time and created a memorable story, they all win.

The purpose of the rules in a D&D game is to provide the structure necessary to cooperatively have "a good time" and "create a memorable story". The "Three Pillars of Adventure" (PHB 8) describe three areas in which the players and their characters can be challenged; exploration, social interaction, and combat. The point of "heroic action" is that it is action that confronts challenges, that has a chance to fail, and that, if it succeeds, represents a victory of spirit or ideal. Using Readied actions to accelerate a spear to light speed, even if 'permitted' by the rules, does none of these things. If run with no chance to fail and used to overcome some in-game challenge, there is no victory of spirit, just a breach in the suspension of disbelief by begging the question of why no one in the world has done this before.

This is not a simulationist game; the rules do not exist to approximate reality.

Nor is it a competitive game, where finding an interesting rules interaction allows one to 'win' and is celebrated as clever play (at least until it gets banned).

Rather, this is a cooperative story-telling game, where the rules exist to permit the resolution of emotionally engaging conflicts.

Combat is the most structured element of a D&D session, with creatures taking turns to make sure that everyone gets a chance to act.

The purpose of a combat turn is to be fair, to permit everyone to have a turn. The purpose of the Ready action is to permit your character to wait until the time is more appropriate for them to act, which both respects their intentions and the principle of everyone getting a turn.

Rules aren't physics

The purpose of the quote is to illustrate the intent of the rules. The rules do not exist to model an in-game reality, nor to be exploited so was to win, they exist to permit the resolution of emotionally satisfying conflicts. If your players are using the rules as written to describe to you how the world works, particularly if they are doing so to create exploits that run contrary to fantasy logic, they are misapplying the rules. If you permit them to do so, you are misunderstanding the purpose of the game.

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Note: I have used PHB 2014 quotes here both because that is what I have access to, and because it is my contention that the intention of the rules has not changed. Comments and edits that update these quotes will be appreciated.