The basic rule

Objectives for this tutorial

  • Learn about the three modes of play
  • Understand the basic rule of a D&D game
  • Understand how to use the basic rule

The three modes of play

In the first tutorial, you learned how a Dungeon Master performs three main sorts of activities: setting the scene, reacting to characters, and refereeing the game.

Similarly, players experience a D&D game in three different modes: exploration, social interaction, and combat. A fun game lets characters experience all three modes of play. Each mode of play can transition to another mode of play. Exploring a corrupted forest might lead to a fight with a dark satyr. When the satyr suffers a grievous wound, the game might tmove from combat to social interaction.

Regardless of the mode of play, the DM continues to perform all three activities of setting the scene, reacting to characters, and refereeing the game. Setting the scene and reacting to characters come from the DM’s imagination and understanding of the game world. Refereeing the game, however, relies partly upon the rules of D&D.

The basic rule

Dungeons & Dragons has a lot of rules to cover the there modes of play. Some rules only apply to combat. Some rules apply everywhere. The great part, though, is that all of the rules really come from one basic rule. This rule covers most actions in the game and forms the basis for many other rules. Once you learn the basic rule, you are ready to referee a D&D game.

So how does the basic rule work?

If a character wants to attempt something where success or failure is not guaranteed, the player (or the DM in the case of an NPC) rolls a twenty-sided die, adds the modifier of the relevant ability, and compares the total to a Difficulty Class. If the roll is equal to or higher than the Difficulty Class, the character succeeds at the task.

For a player, this rule is very simple. The player rolls a twenty-sided die and adds the modifier that you, the DM, tell the player to add.

For you, the DM, the rule is a little more involved because it involves your judgment about the situation and the action being attempted. First, is the outcome in doubt? If the outcome is not in doubt, then you can describe what happens. This is useful for simple tasks that normal people do every day, where success is guaranteed. It’s also useful when the action clearly will fail. For either guaranteed success or guaranteed failure, react with an appropriate description of what occurs.

When the outcome is not already known, you should use the basic rule to find out if the character succeeds or fails at the action being attempted. You need to make three decisions: set the difficulty of the task, choose the relevant ability to the task, and check for special circumstances.

  • Decide the relevant ability: Choose the character’s ability most suited to help him or her succeed at the task. The abilities are Strength, Dexterity, Constitution, Intelligence, Wisdom, and Charisma. For instance, a character attempting to recall how long a dragon’s natural lifespan is will use her Intelligence ability score’s modifier on the roll. You can find the ability’s modifier on the character sheet.
  • Decide the Difficulty Class:
  • Decide if special circumstances exist: If something makes the situation especially favorable to the character attempting the action, then the character has advantage on the roll. This means that player or DM rolls two twenty-sided dice and uses the higher roll in the mechanic. Similarly, the situation abnormally disfavors the character attempting the action, the character has disadvantage on the roll. In this case the player or DM rolls two twenty-sided dice and uses the lower roll in the mechanic.


Let’s say a character in your game is trying to convince a guardsman to let her inside a town. The gate was just closed for the evening, the guardsman sees this sort of exception-wrangling every week. Most of the time it’s related to some shady scheme. The character spins a sad tale about injuries she sustained on the road, making her late to arrive, and how she needs a healer’s ministrations.

Will the guardsman let the character into town? As DM, the answer isn’t clearly success or failure. If it were, you would react. Since the outcome isn’t known, you referee by using the basic rule. You decide three things.

1. The relevant ability is Charisma, because the character uses her personality and words to sway the guardsman.
2. The Difficulty Class is 10 (moderate), because this small town mistrusts strangers after dark but isn’t under some sort of greater threat.
3. There are no special circumstances.


When the outcome is in doubt, when it is not guaranteed that the character will succeed or fail,

1d20 + modifier >= DC means success;
2d20, take the higher with advantage,
2d20, take the lower with disadvantage.

Overview of the example game

The participants in this portion of an example D&D game are

  • Desiree, the Dungeon Master running the game
  • Erika, a player controlling the character Freya. Freya is a fierce and formidable fighter.
  • Quinn, a player controlling the character Rozh. Rozh is a larcenous, laconic rogue.
  • Vince, a player controlling the character Wyst. Wyst is a wily but weak wizard.

Script from the example game


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The basic rule

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