Designer Talk: Can, May, and Must

Designer Talk

Designer Talk

When writing rules text, you might wonder whether to use “can,” “may,” or “must.”

When writing for the Pathfinder RPG*, “can” and “may” are interchangeable game terms meaning “the acting creature has a choice of whether or not to do this.” You can use either one.

For example, in the cloak of the manta ray, it doesn’t matter if you say “The wearer can release his arms from the cloak without sacrificing underwater movement if so desired” or “The wearer may release his arms from the cloak without sacrificing underwater movement if so desired;” they mean the same thing—the wearer has a choice whether or not to release his arms from the cloak.**

“Must” is different, in that the creature is required to do or have something in order to utilize the effect. Compare:

Can: The wearer can sacrifice his own soul as a standard action, healing 100 hit points to all creatures within 20 feet. This kills the wearer instantly.

Must: The wearer must sacrifice his own soul as a standard action, healing 100 hit points to all creatures within 20 feet. This kills the wearer instantly.

The first is clearly an option—a very grim option, but definitely a choice by the wearer. The second is not an option—if you’re the wearer, you have to do this, perhaps because it’s a martyring item.

Examples of magic items using “must” are:

  • eyes of charming (“Both lenses must be worn for the magic item to take effect.”)
  • maul of the titans (“The wielder must have a Strength of at least 18 to wield it properly”)
  • pipes of the sewers (“The piper must continue playing until the rats appear”)
  • various items that require a saving throw (“must make a DC 23 Will save or…”), and
  • various items that require minimums to be able to craft it (“creator must have 5 ranks in the Acrobatics skill,” “creator must be a 10th-level cleric”)


Can and May in Spells

The thing about spells is you’re choosing to cast them. Therefore, everything in the spell that happens automatically already has the “can” or “may” implied in the very nature of being an I-choose-to-cast-this spell. Therefore, you should avoid using “can” or “may” in spell text. Examples:

“You can create a ball of fire that deals 10d6 hit points of damage.” Incorrect!
“You create a ball of fire that deals 10d6 hit points of fire damage.” Correct!

The only time you should be using “can” or “may” in a spell description is if there’s an optional element to the spell that the caster can choose to implement. Example:

“You create a ball of fire that deals 10d6 hit points of fire damage. You can exclude one 5-foot-square from the area of the spell.” Correct!


If you make sure you’re certain whether the acting creature has the option to do something or is required to do something, then your word choice is clear.

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* Other publishers may have their own preferences about which word to use. For example, it looks like Numenera corebook prefers “can” for rules text (“you can apply one level of effort to a roll”, “you can reload and fire in the same action”) and tends to use “may” outside of rules text to mean “there is a possibility that” (“a jack may have an ability that makes her better at speed rolls,” “appropriate camouflage or other gear may count as an asset”). When writing professionally, it’s always a good idea to ask the publisher about this, just in case the publisher has a specific design or style rule about which word to use.

** Magic items in the PFRPG use third-person nouns and pronouns (“the wearer,” “the user,” “the creature,” “he,” “she,” “his,” “her”), which means you often must pick a gender for the hypothetical creature you’re writing about. This third-person perspective is a legacy issue inherited from the D&D ruleset. Different types of rules text in the PFRPG use different perspectives (for example, feats and spells use second-person “you” rather than third-person “the character” or “the caster”), but that’s a lengthy discussion for a different blog post…


4 thoughts on “Designer Talk: Can, May, and Must

  1. So true, but linguistically it drives teacher Alex INSANE that they’re interchangeable because of their practical difference in meaning.

    Not that anyone ever remembers that can asked for ability and may asks for permission anyway….

    Great article as always, Sean!

  2. In game rules, I prefer to use “can” to mean “is possible” and “may” to mean “you have the choice of doing this”. It’s a very small distinction that I only seriously bring to bear on technical, precise games. (I used this distinction on Thunderstone but don’t bother on King of Tokyo.)

    • Oh, I’m just explaining how it is in the Pathfinder RPG (which is based on the WotC periodicals style). I’m *not* saying it’s the definitive way of doing it, or that there was a deliberate choice to do it that way…

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