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A recent question about the necklace of adaptation reminded me of an old question of my own that I've never been able to answer: Can a character wearing a necklace of adaption swim?

It might seem a bit of an odd one, but - Well, here's the two sides of the argument, as I see it:

On the one hand, the necklace surrounds whoever wears it with breathable air. Breatheable air isn't really a medium most adventurers can swim through, so it seems reasonable that an adventurer who puts on a necklace and then jumps out of their boat would find themselves surrounded entirely by air on all sides - and so immediately falling to the lake bottom, the water beneath them continually replaced with more empty air for them to fall through. (Presumably, they'd also emit a great plume of bubbles once underwater as air escaped from their continually-replenished personal air supply.)

On the other hand, the bubble is described as a "shell" of air; Maybe the intent is that a "shell" surrounds the adventurer like some kind of suit, and "sticks" to them instead of bubbling up? If that's the case, I feel like maybe the adventurer would float and able able to swim as normal - or rather, to "fly" inside their bubble - since force would transfer from them, to the bubble, and thus to the water that surrounds it, and vice versa. But that also seems weird, since you'd expect the shell of air to also repel other objects, including adventurer's own clothing and equipment and the ground, and that seems like too important a detail to leave out of the object description.

As a GM, I tend towards simulationist play styles where players are rewarded for coming up with creative uses for magic items - but to do that, I need to have some idea as to how those magic items work.

Is there any text that clarifies how a necklace of adaptation does its thing? Can an adventurer wearing one swim, or are they instead able to walk along the lake bottom? Either option sounds plausible and useful. Which, if any, is correct?

I'm tagging this with 3.5e and Pathfinder because those are the games I'm currently running, but I'm perfectly willing to adapt answers from other editions if there's nothing more immediately relevant. Or from published novels set in official campaign settings, for that matter.

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  • \$\begingroup\$ Hmm. I'm honestly not sure why this attracted downvotes. If anyone has an idea, please let me know. \$\endgroup\$ – GMJoe Dec 10 '15 at 6:27
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As said by others, the problem doesn't arise if you think it's a bubble head scenario or a thin suit of air. The problem seem to arise when you think of the air around you as something more like the shape/size of the "core" aura of Dragon Ball characters.

So let's go through things:

  • Bubble head: Good solution, but unrealistic: the necklace protects the wearer from toxic fumes, so a bubble head would not protect you from acid fumes that would burn the rest of your skin. Unrealistic interpretation, discarded.

  • Thin suit of air: If this is the case, then you'd be able to swim normally.

  • DB-like aura: now things get interesting. There are two options about HOW the necklace works, and they affect the result dramatically:

    • Option 1: The necklace magically transmutes the medium around the wearer into clean fresh air: This is bad. You are basically creating a space devoid of water that is now air, the density changes a lot, you fall down (and, since your maximal speed in air is greater than in water, you'd slam on the ocean floor and take a lot of dmg if you jump out of a boat).

    • Option 2: The necklace basically makes you "wider": only fresh air and no other medium can exist in 30cm around you. This is actually interesting: you have just gained a LOT of water floating power! As per Archimede's principle, you are now moving a lot more water, which is heavier than air, so the upwards resulting force is stronger than without the necklace! Since you can float without it, you can float even better with it! Though normal swim movements would likely be impaired by the unusual situation, but compensated by your increased surface (your increased surface acts like flippers). In this case I'd rule out that you swim at your normal swimming speed, but are twice as hard to sink.

Bottom line: it depends on how you define the necklace's working! Or, even better, take note of these ideas, then let the player describe the act and punish/reward him accordingly :)

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  • \$\begingroup\$ I did think about the whole "acrid fumes" thing, but didn't think it was necessarily relevant. It's magic after all, maybe the charm expands and shrinks as required? \$\endgroup\$ – Miller86 Dec 2 '15 at 10:50
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    \$\begingroup\$ I know it depends on how the necklace works; I'm asking if "how it works" is explicitly stated anywhere. As is, this answer is just restating the question. (I don't want to diss your excellent analysis of the possibilities - But do you know if there's anything that suggests one possibility over the others?) \$\endgroup\$ – GMJoe Dec 2 '15 at 22:41
  • \$\begingroup\$ @GMJoe no harm done :) No, I don't think that it's stated explicitly, but I'd definitely rule out the bubble-head version for the mentioned reason. The thin-suit version is also a bit stretched: if the vapors are super hot/cold, a thin amount of air may not be enough to block the harm, you need more of a buffer. So I'd go with the aura version. Regarding how the aura works (as per answer's analysis), I doubt it's specified in such a detail. \$\endgroup\$ – Diego Martinoia Dec 3 '15 at 11:27
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Compulsory flippant answer

Here is your problem:

Magic does not follow the rules of science. That is why it is magic!

More temperate rules based answer

Notwithstanding, the default assumption in a FRPG is that the rules of science work until the rules of the game tell you they don't.

  1. People in the real world can swim in water therefore people in the FRPG can swim in water. People have, on average, a specific gravity of 0.98 compared to 1.0 for fresh water or 1.025 for sea water, which is why we can swim Human Swimming. Specifically, a living human (i.e. with air in their lungs) will float and this is why divers use weight belts. Now, the deeper you go the denser the water gets so for any object there is a depth where they have neutral buoyancy - for things like steel and rocks this depth may be lower than the ocean floor but there is a cool adventure idea here of the layer of the shipwrecks - sailing at the point of neutral buoyancy.

  2. People in the real world can't breath water therefore people in the FRPG can't either. As a consequence of this there are the conditions "drowning", followed by "unconscious" followed by "dead".

So, along comes a Necklace of Adaptation which changes the rules of science by adding some rules of magic. What it says on the tin is (DMG p.63):

Necklace of Adaptation: This necklace is a heavy chain with a platinum medallion. The magic of the necklace wraps the wearer in a shell of fresh air, making him immune to all harmful vapors and gases (such as cloudkill and stinking cloud effects, as well as inhaled poisons) and allowing him to breathe, even underwater or in a vacuum.

Adopting the WYSIWG principle, it does what it says and nothing else.

You are wrapped in a "shell of fresh air"; the only sensible definition of "shell" (Oxford Dictionaries) in this context is "something resembling or likened to a shell because of its shape or its function as an outer case" where the self-referenced definition is "the hard protective outer case of a mollusk or crustacean". Interesting that it doesn't note that some reptiles have a shell too.

The specific gravity of air (compared to water: typically this is usually referenced to air but we have to keep the same units) is 0.001225. So when you add air to anything you make it more buoyant; this is in fact how ships and submarines made of steel actually float. Since floating = swimming, the necklace will make it easier to swim but harder to dive.

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  • \$\begingroup\$ I guess if the OP really wanted to rule that there should be some additonal buoyancy, you could point out the "This necklace is a heavy chain with a platinum medallion" bit in the description and wave your hands around and say that it balances it out. \$\endgroup\$ – Tophandour Dec 2 '15 at 1:44
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    \$\begingroup\$ You’re not really answering his question, though, since the description does say that the necklace “wraps the wearer in a shell of fresh air,” and you’re not even commenting on that line. \$\endgroup\$ – KRyan Dec 2 '15 at 1:45
  • \$\begingroup\$ @KRyan I agree. This answer merely "states the obvious" rather than tackling the text within the question. \$\endgroup\$ – Ruut Dec 2 '15 at 2:18
  • \$\begingroup\$ Agreeing with KRyan, here: The "allowing to breathe" thing is just one part of the effect description, and you're missing the bit that I'm actually asking about. The point about the laws of physics applying unless otherwise specified is good, but we can't know what effect the laws of physics would have until we know exactly what the necklace does - and so that's what I'm asking about. \$\endgroup\$ – GMJoe Dec 2 '15 at 2:38
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I would say this is a house-rule situation. Two suggestions for the ruling

Bubble Head

As the description only specifies "the wearer" and not anything further, it could be reasonably assumed that instead of a shell of air around the entire character, the shell of air actually just actively exists around the head, or even just the mouth and nose. Hence, the necklace is basically just a scuba mask, and the character can swim as normal.

Diving without a suit

If you prefer it to be a "walk along the bottom" solution, the shell of air extends a very short distance from the character. In this case, the weight of the character and assorted equipment means that the character can walk across the bottom of the body of water. Due to water resistance, the character acts as if on land but slower, rather like being in a heavy diving suit.

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    \$\begingroup\$ If you covered only your head in a breathable bubble, you'd die in a vacuum pretty quickly (and inhaling would make things worse). \$\endgroup\$ – Clockwork-Muse Dec 2 '15 at 13:10

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