What is the source of the "spells do only what they say they do" rules interpretation principle?

Question

Every time somebody asks a question like "can I use X spell for doing Y" the answer is usually "no" because spell descriptions are very short in 5e, and usually they don't explicitly say a spell can do Y.

These answers are based on the "spells do only what they say they do, nothing more" principle.

What is the source of this premise?

Related question: Is there a rule for how to handle creative use of spells?

I'm asking this as a DM. My first thought was "well it is obvious, why should spells do something more". But the more I dig into this topic, the more contradictory arguments I find. I've gathered all thoughts down below, if anyone is interested (upvoted comments indicate that people are).

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DMG examples

The Dungeon Master's Guide has examples of spells doing things out of their originally described scopes:

An area of desecrated ground can be any size, and a detect evil and good spell cast within range reveals its presence. (p.110)

An identify spell reveals that a creature is inside the flask (p.178)

one torch can burn a Huge tapestry, and an earthquake spell can reduce a colossus to rubble (p.247)

Other factors might help or hinder the quarry's ability to escape, at your discretion. For example, a quarry with a faerie fire spell cast on it might have disadvantage on checks made to escape (p.253)

RPG.SE answers

There are highly upvoted answers, implying creative spell usage is a thing in 5e:

Your players are using spells creatively...
That is exactly what D&D 5 encourages.

Open-ended spell descriptions

Some spells have quite open-ended wordings, like Prestidigitation:

harmless sensory effect, such as a shower of sparks, a puff of wind ...

Other spells descriptions aren't very detailed in 5e (compared to systems like Pathfinder), I guess that means it is the DM's job to ultimately say what happens when somebody use a spell in an unusual way.

DMG supports this with its common principle, in Chapter 8: Running the Game (page 235):

Rules enable you and your players to have fun at the table. The rules serve you, not vice versa.

Trusted third-party sources

Some third-party sources encourages stretching spell limitations. See Geek&Sundry "How Watching Critical Role Made Me Better At D&D":

A spell is typically written vague enough that you don’t have to worry about specific limitations unless you’re trying to stretch them. When in doubt, explain to the DM what you want to do and see if they���d be game

See also The Rule of Cool by Matthew Mercer.

Common sense

The strict "spells never do anything their description doesn't mention" principle simply doesn't work. When a player asks "Is Grease flammable?" they already challenge the frame, regardless of the answer. If the DM says "yes", you can ignite the grease. If the DM says "no", you can extinguish flames using the grease.

Of course, since "spells do only what they say they do", DM might say "no" to both assumptions, but this effectively turns a tabletop role-playing game into a pen and paper computer game, boring and awkward. I don't think this is actually RAI.

It seems a DM is supposed to resolve an unusual spell application case, using the intent behind the spell, rather its literal description. For example, it seems reasonable you should be able to use any fire-producing spell to light a torch in a non-combat situation, even when its description doesn't explicitly say that it "ignites flammable things". It heavily depends on the particular DM's style, like many other things in 5e.

What is the source of the "spells do only what they say they do, nothing more" principle?

Answer 1

The rule is an extension of a precedent set by WoTC themselves

The lead rules designer of 5e, Jeremy Crawford, has¹ the power to make official rulings, and frequently does so on Twitter, and in the Sage Advice column on the official D&D site. It's common for him to answer questions with some variation of "if a feature was meant to work that way, it would say so." He has even explicitly stated:

Beware of claims that a rule does something mentioned nowhere in that rule or elsewhere in the core books. There aren't secret rules. (source)

Using this principle, he has made rulings such as:

The Dual Wielder feat doesn't include the benefit of the Two-Weapon Fighting feature. It would say so if it did.
(source)

or

If the grease spell created a flammable substance, the spell would say so. It doesn't say so. (source)

From this, we can derive that barring some explicit clarification from Sage Advice, JC himself, an official errata, or a more specific rule mentioned somewhere else in the game's official material, features in the game are intended to only do what they say. Though, of course, the DM is permitted to make their own rulings and allow spells and effects to do things not directly stated in their description as they see fit.

¹ _{While this status was subsequently backed away from (official rulings only now apply to the Sage Advice Compendium as posted by WoTC, not the tweets from J Crawford), it was true that his ruling was authoritative when this question was asked, and answered; that change in state does not change the overall point.}

Answer 2

I think your issue is more with the nature of discussing the game on the Internet than it is with how the game actually works, should work, or anything of the sort.

We on the internet can only tell you that spells do what they say they do, because we are not DMing your game. We cannot change or expand upon the rules and say “this is part of what the spell does.” We do not have that authority; the DM of the game does, and we aren’t that.

So since we lack that authority, we can only tell you what the books tell you. Anything and everything beyond that is up to your DM (or you, if you are DMing) and not something we can tell you.

Answer 3

This is really the D&D expression of a much broader principle (or, WotC does not hide elephants in mouseholes)

If you look at the history of interpreting organized sets of rules (which is what RAW interpretation of game rules is), you are really looking at the history of law. In a common-law system (like that in the US), judges are tasked with making interpretation decisions about the meaning of statute that are analogous to the rulings us DMs make at our game tables (only with more impact than what we do, of course). To aid them in their efforts, a set of canons of statutory interpretation has evolved over time -- these are the base principles that judges use when reading statutes.

One of them, and the one that Crawford has reframed into our context, is stated most succinctly as "Congress does not hide elephants in mouseholes", or as SCOTUS has put it:

Congress, we have held, does not alter the fundamental details of a regulatory scheme in vague terms or ancillary provisions-it does not, one might say, hide elephants in mouseholes.

(Whitman v. American Trucking Association, 531 U.S. 457 (2001))

So it is with WotC and D&D 5e -- just as Congress is assumed not to hide fundamental alterations of regulatory schemes in ancillary provisions, the D&D 5e team themselves appear to operate under the assumption that their own writings don't try to hide fundamental changes to the workings of D&D in vague text or minor corner-case rules, and the principle that "spells only do what they say" is just a specialization of the general rule that they're trying to instruct us in:

WotC does not hide elephants in mouseholes! (at least as far as D&D goes)

Answer 4

This is how spells are intended to work

According to the developer's commentary, here is the intent behind the rules.

A month later after the question was posted, Jeremy Crawford tweeted:

A spell's text details the spell's effects—the only thing the spell does. Any additional effects are up to the DM.

It seems the spell description covers the basics — a spell does the only thing described in the spell's text, regardless of the situation; it's the DM who might introduce additional effects. This explains why DMG has examples of such "additional effects".

Answer 5

I think an additional reason that should be taken into consideration is for general rulings applicable to organized play.

Having somewhat consistent approaches to organized play is important, and having vastly different rulings on similar spells between DMs in an environment that is designed to support carrying characters from one city to another, changing DMs but carrying everything achieved from previous adventures requires a certain amount of verisimilitude in rulings. The Adventurer's League (and its predecessors) pushes that RAW rulings are of particular precedent in order to create this sense of some continuity. They restrict what can be played, how items can be gained, and more for the sake of consistency.

This means that in situations that are more grey, someone has to be able to make a ruling for play as a whole, and it is likely to be the most restrictive probability. This doesn't, of course, stop you from being able to run a game that is much more loose (and both Jeremy Crawford and Mike Mearls are more loose when they run games from what I've seen), but it does set a standard baseline.

Yes, this is more of a why and not a what, but it is likely a major influence in the what as well.

Answer 6

It is the third sentence of the “Casting a Spell” section in the Player's Handbook.

In the introduction to the "Casting a Spell" section of the Player's Handbook, we see:

Each spell description in Chapter 11 begins with a block of information, including the spell's name, level, school of magic, casting time, range, components, and duration. The rest of a spell entry describes the spell's effect.

So when we ask the question "Is X an effect of spell Y?", the rules tell us exactly how to answer that question: read the spell description.

Answer 7

The Player's Handbook starts off the spellcasting section with this statement:

A spell is a discrete magical effect, a single shaping of the magical energies [...] into a specific, limited expression.

In other words, spells produce a limited magical effect. That limited magical effect is specific, and is described precisely by the spell description.

The conclusion we must then draw is that spells only do what they say they do.