The following are considered to be the most important rules of all d20 games, sometimes called the Ten Commandments of D&D. They’re required reading for anyone new to D&D, but don’t feel like you have to memorize it all before you sit down to play for the first time. Some people take years to learn them!

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1. Rule #1:

Have Fun! – Whatever that means to you. This isn’t a normal game with an arbitrary “win” or “lose” condition… you “win” whenever you’re having fun and you “lose” when you’re not. That’s all there is to it. Any rule that violates Rule #1 is overruled!

2. The Social Contract

This is a game of collaborative storytelling. Since we’re all here to have fun (see Rule #1), we must work together to make sure that the game is as exciting, challenging, and wonderful as it possibly can be. Conflicts of interest will arise and it is the responsibility of all players to resolve these conflicts and ensure that the game is fun and fair for everyone. This is especially true of the Game Master, a player willfully given power by the other players to give form and structure to the story. Players that don’t participate in the action or storytelling of the game or that don’t attempt to resolve conflicts are in violation of the Social Contract.

All players must agree on the terms of the Social Contract for the game to work. See the current proposal from the Game Master here, and decide carefully if you’d like to make any changes.

3. The Core Mechanic

This is a game of choices and consequences. Players choose to take certain actions within the story and these in turn have consequences on the story. Whenever the consequence of a choice made by a player is in question, either because their chance of success or failure is unclear or because their chosen action itself is unclear, then the Core Mechanic comes into play. First, if all players are willing, the choice in question is put to a Vote. All players, including the game master, get one vote. A majority decides what the consequence of the choice will be.

If there is no clear majority after the Vote, or if even a single player does not want to put the choice in question to a Vote, then the consequence is resolved with a Check. This process is described below:

1. The Game Master chooses a number (called a Difficulty Class or DC) that reflects the absolute difficulty of the Player’s chosen action.
2. The Player rolls a twenty-sided die, called a d20.
3. The Player adds to their roll any relevant modifiers as determined by the Game Master or other rules. The total is called their Check Result.
4. The Game Master compares the Check Result to the DC.

If the Check Result is equal-to or greater-than the DC, then the Player’s action is successful; a successful Check results in the player’s choice having the intended consequence. If the Check Result is less-than the DC, then the Player’s action is a failure; a failed Check results in the player’s choice having a consequence determined by the Game Master or other rules.

Once the consequence of a player’s choice has been decided by a Vote or Check, the decision is final and the story continues.

Example A: Grok is a half-giant who’s been locked in a barred cell. The player controlling Grok chooses to have him pull on the bars with all his might, claiming that “No simple bars can hold back the mighty Grok!” The Game Master disputes the claim, saying there’s probably some bars that could hold Grok, but that he’s willing to put this action to a vote. After some discussion, the majority of players vote that the bars of this cell were not designed to hold half-giants, and so Grok is indeed mighty enough to break the bars and escape.

Example B: Grok has gotten himself into trouble again, but this time in a cell built especially for him. When the player controlling Grok tries to break the bars, the Game Master argues that he probably can’t do so and that he’s not willing to put the action to a vote. Thus, Grok is forced to attempt a Strength Check. The Game Master consults the rules and decides on a Strength Check DC of 30. Grok rolls a d20 and it comes up as an 11. He then adds his Strength Modifier of +10, since that is the type of the Check. Since Grok’s total of 21 is less than 30, he fails to break the bars and escape.

4. Simple Rules, Many Exceptions

This game is as consistent and complete as possible. In theory this keeps the game both fair and fun. In practice too many complex rules makes the game neither fair nor fun. As a compromise, we do our best to keep the rules as simple as possible, but to provide as many exceptions to these rules as needed. This helps maintain the consistency of the game and make it easy to learn, while giving players the option to break the rules when they feel that contributes to a more complete experience.

Because this is collaborative storytelling (see The Social Contract), conflicts of interest are inevitable and frequent – thus there are simple rules to help resolve the most common conflicts (such as those rules that define which modifiers apply to a certain Check), and then there are thousands of exceptions to help resolve less common conflicts (such as those rules that define whether a player can initiate a certain action). Players are responsible for knowing the simple rules, while the Game Master is also responsible for knowing many exceptions.

Example: Normally a player’s character can only attack on that player’s turn. However, exceptions exist for so-called “attacks of opportunity” which are granted to a player’s character when another character performs an action that would obviously put them at risk of being attacked. This could be when your Fighter stands ready to swing his sword as the Wizard casts a spell, or the Ranger draws her bow, etc.

5. Specific Beats General

If a new or specific rule contradicts an old or general rule, then the newer, more specific rule wins. Simple rules tend to be the older, more general rules, and the exceptions tend to be the newer, more specific rules. This is what allows the exceptions to break the rules as described above (see Simple Rules, Many Exceptions). “Specific” in this sense refers to rules that apply to a smaller number of cases, or that apply less often, than “General” rules. “New” in this sense refers to rules that were published more recently than “Old” rules. This means that the rules published for Pathfinder take precedence over the rules published for D&D 3.5, which themselves take precedence over the rules published for D&D 3.0. Thus, it’s important to know relatively when rulebooks were published, and whether there has been an update to their rules (in later editions, errata, or in house rules). Again, the Game Master is responsible for knowing the specific rules and the edition in which they were published, while the other Players are responsible for knowing the most up-to-date general rules.

Example A: As above, normally a player’s character can only attack on that player’s turn. That’s the general rule, but a set of specific rules (exceptions) exist for attacks of opportunity – or attacks that can be made during another player’s turn when they attempt a risky action. Each of these rules covers one case where the defending player’s risky action is shown to trigger, or provoke, an attack of opportunity – this is what makes them specific and not general rules. Many rules use the word “normal” or a variation on it to differentiate general rules from specific rules.

Example B: In the D&D 3.5 Player’s Handbook it states that if a player selects to play as a character of the Human race, then that character receives no bonus to an ability score. However, in the Pathfinder Core Rulebook it states that if a player selects to play as a character of the Human race, then that character receives a +2 bonus to the ability score of the player’s choice. Which is correct? Answer: choose the Pathfinder rule for the ability score bonus of the Human race because it is the most recently published rulebook to address that particular rule.

6. Fluff vs. Crunch

The intention and mechanics of the rules should make the game more fun, not less. Rules provide the form and structure of the game, enabling and inspiring the player’s actions – they are not meant to disable or limit the player’s actions. Whenever a rule is in question, either because a player feels that the rule is not clear (such as when it is an old, specific rule and there is a new, general rule in play) or because one, but not all, of the players feels the rule is not fun, the following process is used:

1. All players read the printed text for the rule, including examples and descriptive text.
2. Each player decides for themselves which parts of the rule are “fluff” (defined as flavor or descriptive text that instructs the player as to the intent of the rule) and which parts of the rule are “crunch” (defined as the technical or mechanic text that instructs the player how the rule works).
3. Players now participate in two rounds of Voting. In the first round, players vote on whether they feel that the intention of the rule is clear, given the “fluff” of the rule. In the second round, players vote on whether they feel that the mechanics of the rule are clear, given the “crunch” of the rule.
4. If the majority feels that both the intention and mechanics of the rule are clear, then the most strict interpretation of the rule is applied.
5. If the majority feels that the intention of the rule is clear, but that the mechanics of the rule are unclear, then the most open interpretation of the rule’s mechanics is applied within a strict interpretation of the rule’s intention.
6. If the majority feels that the intention of the rule is unclear, but that the mechanics of the rule are clear, then the most open interpretation of the rule’s intention is applied within a strict interpretation of the rule’s mechanics.
7. If the majority feels that both the intention and mechanics of the rule are unclear, then the players collectively create a new house rule that would be most fun for everyone. House rules are considered the newest, most specific rules and require unanimous consent from all players before being created.

The Game Master is responsible for maintaining the consistency of the rules interpretations and the list of house rules. The Players are responsible for informing the Game Master when they wish to dispute a rule, or they aren’t sure if they are applying a rule correctly.

Example: This rule is difficult for new players to understand, so here’s a longer example. In D&D 3.5, a prestige class is a class with requirements. A rule states that a character must meet the requirements of the prestige class both to enter the class, and to continue advancing in the class. Keep this in mind and consider the Ur-Priest, a prestige class with the following “fluff” and “crunch:”

Ur-priests despise gods. However, a small number of
them have learned to tap into divine power and use it for
their own needs without praying to or worshiping a deity.
…
A member of any class can become an ur-priest, even—
and in fact, especially—an ex-cleric.
…
REQUIREMENTS
To qualify to become an ur-priest, a character must fulfill all
the following criteria.
…
Special: The character must have no ability to cast divine
spells. If such spellcasting ability was previously possessed
(as with an ex-cleric), that ability is forever forsaken.
…
CLASS FEATURES
…
Spells per Day: An ur-priest gains the ability to cast a
number of divine spells.
…

The “fluff” (all the items before the listed requirements and class features), clearly shows that the intent of the prestige class’s special requirement (that the character have no ability to cast divine spells) is meant to emphasize that normal divine casters (such as clerics) must forsake their ability to cast spells before they can advance in the class. However, the “crunch” of the rule, which includes the requirements and class features, is problematic because its interaction with the general rule (that a character must meet the requirements to enter and CONTINUE TO ADVANCE in a prestige class) is unclear. When the Ur-Priest “gains the ability to cast a number of divine spells” does it then no longer qualify for its own requirement that “the character must have no ability to cast divine spells?” Such a case, where gaining levels in a class prevents you from gaining more levels in that class, is unprecedented in the rules.

In this case we apply the process described above, namely we apply the strictest interpretation of the intention of the rule: the Ur-Priest is a divine spellcasting prestige class intended for characters that do not already possess divine spellcasting and this restriction is not intended to prevent Ur-Priests from advancing in levels; and then we apply the broadest or most open interpretation of the mechanics of the rule: the Ur-Priest may continue to advance after they have gained divine spellcasting because this class feature does not explicitly state that it prevents advancement in the prestige class.

This may seem like common sense, but not all applications of the Fluff vs. Crunch rule are this straightforward.

7. Open-Ended Gameplay

The main feature of roleplaying games is that players can do whatever they imagine. There is nothing you can’t do in a tabletop or live-action roleplaying game, and nothing is unprecedented. That’s what makes these games unique.

However, just because there isn’t a rule to apply to what you want to do, or a specific case is omitted from a general rule, that does not mean that you may automatically choose the most open interpretation of your choice. A rule or house rule must exist for every action that is available to players in the game; if a rule or house rule does not exist for a given action, that action is not available to the players. Just because the rules don’t say you can’t do something, that doesn’t mean you can. In general, if a player proposes an action which is not explicitly covered by the rules, then the players should either substitute an existing precedent rule or they should create a new house rule to apply to the action.

The inverse of this rule is also true. Just because the rules say that you can’t do something, that doesn’t mean you can’t. In other words, every rule that prohibits a player from doing something in the game has an exception of some kind. All a player needs to do to overcome the limitation is to find the exception. If no exception currently exists, then it is the responsibility of the players to create a new house rule to that effect.

Example: The Wizard Gnome studies an Adamantine Golem before casting a spell. The Game Master tells the player that the Golem is Immune to Magic, which blocks any spell or spell-like ability that is affected by Spell Resistance. The Wizard realizes that this immunity would block the majority of her prepared spells, and she struggles to find a way to defeat the Golem. Eventually, she remembers that even though creatures are normally summoned on the ground, the “crunch” for Summon Monster 7 states only that “Creatures cannot be summoned into an environment that cannot support them” and that the Mastodon’s normal environment is “cold or temperate forests and plains.” The “fluff” is silent on whether creatures were intended to be summoned on the ground or in the air (since some of the listed creatures are naturally airborn, etc.). Since the battle is taking place on a temperate plain, the Wizard reasons that she can use her spell to summon the Mastadon anywhere in range (this is, after all, an environment that can support it). She notes that the “crunch” for Summon Monster 7 does not state whether the creature must BE supported – only that it must be summoned into an environment that CAN support it. Thus she chooses to summon the Mastodon above the Adamantine Golem’s head in an attempt to crush it with the creature’s sheer weight.

Effectively the Gnome exploited an ambiguity in the wording of her spell to attempt to defeat the Golem. This may or may not be acceptable to the other players, but more importantly, it doesn’t help her to defeat the Golem because there are no rules for actually calculating the damage the Golem would take. A precedent rule might be the Table for Damage from Falling Objects, but objects and creatures are typically treated separately by all game rules. According to the Open-Ended Gameplay rule, creative gameplay like this should be encouraged, but players cannot simply perform any action not expressly forbidden by the rules. In this case, the Player controlling the Gnome has a responsibility to use existing rules that bypass the Golem’s Immune to Magic trait. Because other options exist, such as using Summon Monster 7 normally and casting other spells that aren’t affected by Spell Resistance (or the Transmute Metal to Wood spell, an explicitly stated exception to the Golem’s Immunity to Magic), other players have no obligation to agree to a new house rule that will cover this new application of the Summon Monster 7 spell. Of course, players can elect to make a new house rule anyway, or to dispute the Gnome’s interpretation of the spell.

8. Round Down

When performing calculations, round down any fractional values by default. Round down even if the remainder is 1/2 or more. This helps to keep the game more balanced.

The spirit of this rule applies to other aspects of the game as well. If a rule or action by a player would potentially unbalance the game, play on the safe side rather than taking a risk by choosing the strictest interpretation of the rule, or have the player change their action to reduce the potential for imbalance.

9. Multiplying

When performing calculations, apply multiplications differently for abstract values than for real-world values. For all values that correspond to real-world measurements, such as distance or time, multiply as normal in the game’s calculations. However, if a value corresponds to a game-abstraction, such as damage, use the following process:

1. If only one multiplier applies to an abstract value, multiply as normal to generate the resulting value.
2. If two or more multipliers apply to an abstract value, subtract one from all multipliers other than the first one, then add the multipliers together, and finally multiply the sum with the abstract value to generate the resulting value.

This helps to keep the game more balanced. The spirit of this rule applies to other aspects of the game as well. The rules should not emphasize the accumulation of force multipliers at the scope of game mechanics. Instead, tactics and strategy should provide the greatest benefit for players in their attempts to overcome challenges.

Example A: A double damage multiplier (×2) and a double damage multiplier (×2) applied to the same attack’s damage results in triple damage (×3, because 2 + (2 – 1) = 3, not quadruple damage (×4, where 2 × 2 = 4).

Example B: A creature whose size doubles (thus multiplying its weight by 8) and then is turned to stone (which would multiply its weight by a factor of roughly 3) now weighs about 24 times normal (because 24 = 8 × 3), not 10 times normal (where 10 = 8 + (3 – 1).

10. Stacking

No bonus may be stacked indefinitely. Stacking refers to the act of adding together bonuses or penalties (modifiers) that apply to one particular Check, dice roll, or statistic. Generally speaking, most bonuses of the same type do not stack. Instead, only the highest bonus applies. Most penalties do stack, meaning that their values are added together. Penalties and bonuses generally stack with one another, meaning that the penalties might negate or exceed part or all of the bonuses, and vice versa.

This helps to keep the game more balanced. The spirit of this rule applies to other aspects of the game as well. Any combination of rules that results in an easily exploitable, potentially infinite bonus to a check, roll, or other action of benefit to a player is not allowed. When these infinite exploits are discovered, a house rule must be created to prevent the exploit.

Example: Our example human has a base speed of 30 feet. In chainmail, that drops to 20 feet (see Table 7-6 in the Player’s Handbook).

The character has two enhancement bonuses to speed (+10 feet from the boots of striding and springing and +30 feet from the expeditious retreat spell). Since they’re both enhancement bonuses, they overlap, and the character can use only the higher bonus. Obviously, the +30 feet from the expeditious retreat spell is the speed bonus to use, but how does that interact with the reduced speed from the chainmail?

Always apply increases to a speed before making any adjustments for armor or encumbrance (see Tactical Movement, in Chapter 8 of the Player’s Handbook). The expeditious retreat spell adds +30 feet to our human’s base speed of 30 feet, which yields a speed of 60 feet, which chainmail reduces to 40 feet (see Armor and Encumbrance in Chapter 2 of the Dungeon Master’s Guide). The boots are still working, however, so when the expeditious retreat spell ends the character still has a slight speed increase. The character’s base speed is still 30 feet, +10 from the boots, which chainmail reduces to 30 feet (also from Armor and Encumbrance in Chapter 2 of the Dungeon Master’s Guide).

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It’s not absolutely necessary to memorize all these rules before beginning your first game of D&D. Just know that you’ll be responsible for following them, and if you forget one you’ll be gently reminded.

If you forget one on purpose you’ll get a book thrown at you!