844639_68059171sEvery campaign needs a game physics, whether the GM knows it or not. And, in fact, they all have one, whether it’s specified or not, and whether the GM knows that or not, as well.

Boy, that was a short article! Now that we’ve established both need and solution, can we move on to another topic, because this one sounds both geeky and boring? Well no – not so fast, fly-boy.

Why? What’s a “Game Physics” for, anyway?

The Game Physics is what the GM uses to decide anything that’s not explicitly stated in the rule books. It’s also what the GM uses to comprehend and interpret those things that are explicitly stated in the rule books, and the standard of comparison for cases where one of the rules doesn’t work – either producing nonsensical results or being in aparrant contradiction with another rule. It’s the GM’s understanding of how the game world actually works.

The Usual Game Physics

Most GMs don’t explicitly spell out a Game Physics, don’t analyse things to that level of detail, either for themselves or for their players. They make rulings based on one all the time, mind you, but never put together a comprehensive picture of the inner workings of the universe, relying on “the usual game physics” – which is to say, they rely on their understanding of how the real world works, and rule that the book’s description of the various unusual phenomena possible within the game system constitutes the equivalent of the laws of physics for those particular subjects. And, most times, that’s all the players want or need.

From time to time, the GM will make a game ruling (which should get added to the House Rules of the campaign to maintain consistancy). Each such ruling should either be explained by the existing Game Physics or should expand apon it.

For example, it’s very easy to take player knowledge of physics and apply it to the game world. Lever action, harmonic oscillations, centrifigal force, gunpowder and plastic explosives, plastics, rifled gun barrels, electronics, microchips, pocket calculators, etc. The GM is perfectly entitled to rule that any or all of these don’t work in a fantasy campaign in order to preserve the level of technology within the game at an appropriate level. Every time he does so, he is changing the physics of the world in ways he probably doesn’t understand.

So why go beyond that?

An excellent question. There are multiple benefits to a more explicit approach to defining a game physics.

First, it puts players and GM on common ground. They will know right off the bat that certain things won’t work, so don’t bother trying them – which in turn helps them stay in character by only doing things the character expects to work.

Second, if the GM extends his understanding of the game physics beyond that of the characters, he can maintain consistancy of rulings and technology even if the game develops into untapped areas of high-technology. This is obviously valuable in certain genres – SciFi and Superhero being the obvious ones. It means that the players and NPCs are playing by the same ground rules, whether they know it or not – if a PC attempts an experiment which reveals a physical principle that they didn’t know, they will get an unexpected result and an explanation for certain things that may have happened in the campaign’s past. They can even extend the game physics beyond it’s starting point if they are so inclined. Instead of technobabble, we have technology – with limits and failure modes and creative applications.

I would contend that the same is true in any campaign – only the specific subjects change. In a horror campaign, the better the GM understands the “mechanics” of summonings and metaphysical manifestations, the better he can run such games. In a fantasy campaign, the more he knows about how magic actually “works” in the game world, the more he can push beyond the rules as and when necessary – something I touched on in a previous post (A Quality Of Spirit: Big Questions In RPGs).

Third, it makes the job of being a GM easier, and quicker. Instead of having to mull deeply over questions and their implications when they arise, an understanding of the game physics often lets the GM make an immediate ruling without batting an eyelid and get on with the game.

And finally, it adds extraordinary depth and verisimilitude to the campaign. Instead of a shared fictional world, it starts to feel like a real world that the characters happen to live in. This last has been known for as long as there has been science fiction – you have to establish the ground rules before readers can really get into the story. Read any SF novel, and you’ll find that a key element of the first quarter or so of the book is an establishment of the scientific principles that matter to the story. Read a short story, and you’ll generally find it in the first couple of paragraphs, certainly within the first two pages. A side benefit of doing so is that even when contradicted by later scientific discoveries, a story can remain timeless if the story is good enough – examples include the Lensman series (E. E. ‘Doc’ Smith), the Skylark Of Space series (‘Doc’ Smith again), the Incompleat Enchanter series (L. Sprague DeCamp and Fletcher Pratt), the Black Cloud (Fred Hoyle), The Known Space series (Larry Niven), and the list just goes on and on and on from there. Contrast this with any of the… poorer SF of the past century, and you’ll find that either this material is absent, or it’s so abstruse that most readers can’t follow it (or get bored trying).

In a nutshell, it takes the flash-bang-wizardry out of the picture and lets a story be judged on its merits as a story. Applying the principles to an RPG brings the same benefits to the game.

The Downsides

It can be a lot of work doing a comprehensive game physics (it can also be a lot of fun). But the real downside is that it can be harder to impart a sense of wonder.

I would contend that modern audiances/players already find that harder to tap into, another subject that I’ve written about in the past (Are Special Effects Killing Hollywood?).

So it can be argued that adding additional impediments is the last thing that you should be doing. It can also be argued that part of the GM’s job is fitting the game to the expectations of the players, and that modern players mandate a modern approach – and GMs should be grateful that there are ANY side benefits in doing so. I’d love to hear other people’s thoughts on this subject!

The Conservation Of Counterintuition

Another common approach is to rule that if a phsyical law seems counterintuitive, or just too difficult for the GM to understand, or requires higher mathematics, it just doesn’t work. That means that most GMs draw the line at Relativity – anything more complicated (including relativity itself) is out, anything less complicated is in. This is true even in modern and sci-fi campaigns. Any technology appropriate to the game era that relies on those physical priciples still works, but the physics are different because the complicated stuff just isn’t there.

Of course, different people will have different levels of understanding of physics; what seems obvious to me may not be obvious to them, and vice-versa. But as a rule of thumb, this one principle is enough definition of a simple game physics to make it useful.

The Metaphilosophical Properties of Genius

When I first started GMing, this was the game physics that I came up with, and it’s still perfectly servicable. It derives from the fact that physics and chemistry and science in general used to be known as “Natural Philosophy”. The concept is that the state of knowledge contemporary to any time period is a complete and accurate description of the way the physics of the time period actually works, but that occasionally individuals come along of sufficient intellect to (literally!) reshape the world with a deeper understanding. Thus, heavy objects fell faster than light ones until Gallileo performed his famous experiment to prove that they fell at the same speed.

I even evolved a house rule: 5 points of intelligence above whatever constituted “genius” permitted one breakthrough with sufficient effort. On that basis, Sir Isaac Newton gets an INT on the D&D scale of about 60, Nicola Tesla gets a score of about 45, and Gallileo rates a 40. If you had a little less than this, and spent twice as long on it, your theory might also be correct – but would take decades or even centuries to become accepted.

Evolving a unique game physics for your campaign

Okay, so (assuming that I’ve convinced you that having one is worthwhile), just how do you go about constructing a game physics for your campaign?

Well, you start with one of the three foundations described above.

You then go through the rulebooks of the game you are running and add explanations (in terms of physics) for anything they permit that the foundation physics doesn’t cover. It might be “magic works”. It might be “the gods are real.” It might be that “morality has measurable physical effects” (lawfully-aligned weapons doing extra damage to chaotically-aligned targets and so on). It might be “FTL is possible”, or “superpowers exist”, or “time travel is possible”.

Each time you add such an item to your game physics, re-examine the central concepts of rules and genre and cross off anything that is now explained. For example, one theory as to the nature of divinity might also cover the “morality” question above, while another did not.

These explanations can be as extensive or simple as you like – a single sentence, or multiple pages.

At every stage, you have the option of deciding that this part of the game rules simply doesn’t work in this particular game – decisions that can have significant repercussions; see, for example, Garry Stahl’s article on removing alignment from his campaign. D&D without magic, or without gods, would be no less significantly altered.

You can also explicitly remove selected parts of a subject, or give them additional explanation that radically reinterprets them. D&D without Necromancy is an example of the first; the treatment of Illusions in my Shards Of Divinity campaign is an example of the latter, one which I’ll blog about some other time.

Once the rules and genre conventions are fully dealt with by the game physics, the next step is to think about anything else that makes this particular game, and game world, unique, and make sure that they are also covered by the game physics. An example of this is the Cyphergate in Johnn’s Riddleport campaign-in-development.

The final step is to go over the compiled Game Physics and create any house rules that are needed to put a game mechanics interpretation on the principles you’ve devised.

How Much Should You Tell Your Players?

Your first house rule should usually be that there is a Game Physics and that it will be used as the basis of any rulings that you are called apon to make as GM. The Game physics determines what is possible and what is not.

My players have come to expect a fleshed-out game physics lurking in the background of my campaigns, so I don’t need to include this, but WOULD need to warn them if it was not the case.

After that come any house rules that result.

I DON’T necessarily tell the players what the game physics actually are – how many characters would actually know that? Instead, I let the players seek to deduce the physics from their interaction with the world. I might let the occasional principle dribble out in response to particular skill rolls if they are relevant, but that’s as far as it goes.

How Much Should your NPCs know?

Another trick that I’ve found useful is to rate each line in the game physics in terms of how abstruse the knowledge is on a scale of 1-4. This permits me to edit copies of the game physics into formats describing the knowledge level of commoners, educated laymen, well-educated nobility, experts/sages, and GM only. Anything beyond their level of understanding is replaced with a dumbed-down version or the simple statement “it works”.

Commoners in an uneducated society get nothing more than the foundation rule and “it works” for everything else. And – for authenticity – I’ll sometimes insert deliberate fallacies and misunderstandings and superstitions. Experts will get only one or at most two of the advanced principles, in all other respects they are at the level of educated laymen; Sages also only get one or two advanced principles, and are considered to be at the level of well-educated nobles otherwise.

I find it easiest to go from most educated to least educated – the GM knows it all, so he gets the actual game physics, everyone else will have less than that. When inserting falsehoods and fallacies, I will work back up the heirarchy, adding comments such as “The common supersitition is (blah blah blah)…”

The result is a “bible” for the roleplaying of different levels of education within society that ensures consistancy. After you’ve used them for a while, the consistancy of format that results from editing a copy of an existing document makes finding what you’re looking for second nature, and you will often not even need to refer to these “bibles”.

Going Further

Another key point that’s worth remembering is that the game physics can always be revised or extended. It represents the combined level of understanding of a collection of contemporary experts, and is not necessarily gospel – and is certainly not the last word. Thus, if any problems arise within the game physics, those physics should evolve to encompass a solution and an explanation. This may move the game physics a little closer to the real world, or it may make it stranger.

It can be very useful to have some knowledge of how certain physical laws were proven, as these will inform you of how things will be different in your world. For example, you might decide that sound and light travel at the same speed – in that case, you would hear the thunder at the exact same time as you saw a flash of lightning, and would hear the axe chopping the tree in perfect time with the motion of the axe-head striking the wood. (I don’t know why you’ld bother with that one, personally, but it’s just an example).


The obvious ramifications have already been mentioned, in the earlier section detailing why a Game Physics is worth having. But there are also some more subtle consequences that are worth mentioning.

The first of these is that each game physics lends a subtly-different flavour to each different campaign. Even though they use the same core rules, my Shards Of Divinity campaign is distinct from my Fumanor Campaigns, which was different from my Rings Of Time campaign. While some of that derives from the characters and some from the differences in adventures, some of it is a spice from the game physics.

Secondly, there is a continuity of such flavours from one campaign in the same game world to another; it’s not just as shared history that connects the two Fumanor Campaigns that I currently run with the predecessor campaign, they feel like they’re taking place in the same world.

Thirdly, the game physics can form a common foundation amongst several GMs, permitting a shared world experience that I can’t believe would be possible any other way.

And finally, it makes it easier to keep one campaign distinct from another – an absolute necessity when you run as many of them as I do!

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