If someone has Reduce/Enlarge Person cast on them, does equipment picked up later (after the initial casting) resize?

Question

The rules for enlarge person and reduce person say "All equipment worn or carried by a creature is similarly [reduced or enlarged] by the spell." Does that happen once at the beginning of the spell for the duration of the spell or do other things picked up later also change in size?

Which one of the two is it, and wouldn't the latter have really strange consequences, such as if you pick up a friend all their equipment (but not the friend itself) would become while you carry it/him?

Inspired by this question.

Answer 1

The enlarge happens only at casting time.

RAW explanation

Both spells explicitly state that "Any [enlarged, reduced] item that leaves an [enlarged, reduced] creature's possession (including a projectile or thrown weapon) instantly returns to its normal size." Since they don't mention any size change when entering such a creature's possession, it's safe to assume they intentionally didn't include it because they didn't intend it to happen.

Game balance explanation

Essentially you have covered the reasons why this is the way the spells ought to work for balance purposes. A lot of funky behavior is possible when items are enlargeable; however, enlarging a person is far less useful if you can't enlarge their weapons, clothing, and armor, as well. Presumably, instead of drawing the line at "worn or held", and having the tricky "backpack grows, contents don't" situation, they include everything carried and not just held.

Game physics explanation

For a "realistic" justification of this behavior, think of it as a magic field initially shrink-wrapping the creature and its possessions, enchanting it, and then dissipating. When an item exits the shrink-wrapped area, it returns to its mundane size and the shrink-wrap shrinks to its new shape. Picking up an ally, then, won't add the ally or his gear to the shrink-wrap.

Answer 2

All items wielded by the character are enlarged, regardless of when they're picked up

As per the text of Enlarge Person

All equipment worn or carried by a creature is similarly enlarged by the spell

Now let's look at the pathfinder spell rules, specifically the Duration header And the spell has a duration that is not instantaneous, so the duration is a timed duration

Timed Durations: Many durations are measured in rounds, minutes, hours, or other increments. When the time is up, the magic goes away and the spell ends. If a spell's duration is variable, the duration is rolled secretly so the caster doesn't know how long the spell will last.

And it affects a creature directly, so

Subjects, Effects, and Areas: If the spell affects creatures directly, the result travels with the subjects for the spell's duration. If the spell creates an effect, the effect lasts for the duration. The effect might move or remain still.

Therefore, we know that the "equipment (...) carried by the creature" effect moves with the creature, and lasts for the duration of the spell, meaning that any items picked up by the creature after the moment of casting are also affected by the spell and enlarged.

Answer 3

I tend to agree with @TheRubberDuck. It is all in the nuance, and the verb tense, of the spell as written:

All equipment worn or carried by a creature is similarly enlarged by the spell.

So, all equipment worn or carried by a creature at the time of casting is similarly enlarged by the spell. The magic has been cast at this point, there is no new casting of the spell happening, or transference of the spell as a character roams around and picks things (or people) up. Also note:

Any enlarged item that leaves an enlarged creature’s possession (including a projectile or thrown weapon) instantly returns to its normal size.

So if your target character/creature holds onto another, secondary character/creature while he is being Enlarged the spell could arguably affect the secondary creature, but only while being held by the target of the spell.

I would argue the same for Invisibility, for instance. If a half-orc let a halfing ride on his shoulders and was made invisible, they'd both be invisible, but once the halfling left the half-orc they would visible again. The wording in Invisibility is a little clearer, emphasis my own:

Items dropped or put down by an invisible creature become visible; items picked up disappear if tucked into the clothing or pouches worn by the creature.

So, when an invisible creature picks something up and hides it on their person it doesn't become invisible itself, it becomes invisible because of it's circumstance hiddin within and invisible creature's garments. With regards to Enlarge, I'd apply the same logic--the spell doesn't pass on to something picked up.