The Air-Breathing Mermaid Problem

Every now and then when playing RPGs you stumble upon a mechanic that solves a problem you didn’t know you had. This situation is called the Air-Breathing Mermaid Problem, based on a meme that goes something like this:

A game has mermaids, they are introduced in the core book. The entire book makes you believe mermaids can breathe both air and water - there is nothing to contradict this assumption. However, when a supplement comes, you suddenly discover that you have a new power that lets mermaids breathe air. You were just given a solution to a problem you didn’t know you had.

The same problem can manifest itself in different ways. You could have a poorly checked book that only lists offhand penalties to using a weapon in an ambidextrous merit that removes said penalties, or come from a specific character focus that brings a mechanic to a focus that would otherwise have been glossed over by the GM.

In our recent game of Fellowship, we had a character playing the Angel playbook. One of the core powers of that playbook, is that it can speak with the language of all things, and with some equipment, it can also understand any spoken language. Since our game is about exploring space and talking with aliens, was it not for this move, it would be a default that we can communicate with the aliens through some sort of babel fish or what have you, but with the powers that playbook introduces, either only that player can talk to most aliens, they translate for everyone and we mostly ignore that rule, or we ignore that rule and everyone can speak freely.

While this example is pretty specific, it could be similarly applied to any system that features a way to learn languages - if one player invests heavily into being a polyglot, it can either punish everyone else for not speaking the language, or punish the linguist for wasting so many points on languages.

In most other situations, it’s rather uncommon to come across the Air-Breathing Mermaid Problem, but it could be a good design decision to try avoiding small mechanics and extra powers that solve very specific problems. Sure, being ambidextrous can be fun, but are offhand penalties important enough to warrant their own exceptions to the rule? Is it important that a mermaid can’t breathe air? If the answer is no, maybe it’s best not to solve problems nobody is having…

I wonder how much early simulationist RPG material could be trimmed using this “pattern”; calculate the “cost” of an given power or rule. :thinking:

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From the referenced history of gaming - Origin of 'Air-Breathing Mermaid Charm' - Role-playing Games Stack Exchange

The ‘Air-Breathing Mermaid Charm’ is a useful descriptor for a certain kind of negligence in writing of RPG books, and particularly their rules. Usually it means approximately the following phenomenon: a mermaid write-up says nothing about breathing (making it easy to assume that the setting’s mermaids, being half-humanoid-half-fish, can breath both in air and water, much like mermaids in various other works of fiction), and then later a Charm says that it enables air-breathing for mermaids (i.e. it solves a huge, blatant problem that wasn’t made know to even exist beforehand).

But I would like to know whether this is an actual race in some of the books and an actual Charm, or is it a purely apocryphal example that is very loosely based on various less catchy-sounding Charms in the game? If the former, what book(s) is the example from? If it’s the latter, what canonical examples is it based on?

And answer:

No, it wasn’t an actual charm. It’s a meme/out-of-game jargon.

I suspect that the origin of this phrase was a thread on the old White Wolf forums that have now been deleted, since I can’t find the original post with Google.

In essence, the idea of the Air-Breathing Mermaid Problem is a criticism of a mechanical widget (spell, power, piece of gear, etc) that allows a character to do something that would have generally been held to be implicitly possible without it, which is usually added in a supplemental book - the archetypical example of which would be a hypothetical spell that allows mermaids to breathe air. Before the spell was published, the general assumption would be that mermaids would be perfectly capable of breathing air as well as water, but afterwards, it implies that no, mermaids can’t breathe air unless they cast the spell first.

It can then be rephrased as “Air-Breathing Mermaid [Mechanical Widget]” like the “Air Breathing Mermaid Charm” you were asking about in the Question, to refer to the specific type of mechanical widget that you’re referring to.

An example of this sort of thing in Exalted is the 2e supplement Oadenol’s Codex introducing expanded rules for magic item creation, which included a number of minimum stat requirements to do so, as well as rules for how different qualities of crafting workshops interact with the process. In the 2e core rules, there was a Charm named Craftsman Needs No Tools which negates the penalties for not having tools; in Oadenol’s Codex, it specifies that it only counts as a particular level of workshop (imposing penalties on rolls to craft magic items), and then introducing a new Charm that negates these new penalties.