What happens to a medium whip's reach when Enlarge/Reduce Person changes its size category?

Question

What happens to a whip when it is under the effects of enlarge person or reduce person?

As far as I know whips are the only melee weapon with a range. I am not asking about weapons with reach as those are understood.

There are two whips, the normal whip which is a exotic one handed melee weapon, and the scorpion whip which is a exotic light melee weapon. A whip's damage is 1d2 Small, 1d3 Medium, and 1d4 Large. A scorpion whips damage is 1d3 Small, 1d4 Medium, and 1d6 Large. I could also calculate HP, weight, and price but again those are easy to figure out.

What I don't know is how the 15 foot range is affected. Under the weapon descriptions, nothing is mentioned for either Small or Large variants of the weapons, granted it's assumed the description is talking about Medium versions since most playable races are Medium, and most rules are written for Medium.

My thought is that the whips' reach is affected by the character's natural reach. So Small, Medium, and Large (long) characters can all reach 15 feet. Tiny characters could reach 10 feet. Large (tall) and Huge (long) characters could reach 20. So basically the whip is granting an extra 10 feet of reach to your natural reach. However I have no proof or evidence of this, and because I have an interest in this, I am also biased towards this answer.

Answer 1

James Jacobs says a typical whip sort of triples a creature's reach

Paizo creative director James Jacobs says in this 2012 post that a whip triples a typical Medium or bigger creature's reach and allows attacks by typical Tiny creatures from 10 ft. away and, perhaps, by extension by typical Diminutive creatures from 5 ft. away.

While Jacobs isn't a source for errata, he's cited in a 2012 thread to which received several FAQ votes before the Paizo staff felt no response was necessary. This, of course, contradicts the statistics for the balor but otherwise seems playable enough.

Answer 2

No one knows.

For regular reach weapons, your reach is doubled—so when you get bigger and your natural reach increases, your reach-weapon reach increases proportionally.

But whips are a weird exception: it just says it has a 15-foot reach. You could be overly literal and interpret that to mean that whips always have a 15-foot reach, no matter the size of the whip and wielder, but that’s remarkably inconsistent with every other weapon in the game, not to mention pure nonsense with respect to how whips work (then again, not being able to threaten with a whip is if anything even more nonsensical—“attacks of opportunity” are literally the only thing a bullwhip can actually be said to be good for in combat).

So no one thinks that the reach should stay at 15 feet. The question is, what does it become?

The first Google hit for this question is this Paizo thread, and literally the first two responses assert two completely different interpretations:

• The whip gives you +5 ft. more than you would normally have with a reach weapon. So if a Large creature normally threatens up to 20 ft. with a reach weapon, with a whip it threatens 25 ft.

• The whip gives you triple your natural reach. So if a Large creature normally threatens up 10 ft. without a reach weapon, it threatens 30 ft. with a whip (instead of 20 ft. with a regular reach weapon).

There is nothing in the rules that covers which of these two options is the case, and to my knowledge no Paizo developer has ever commented on the problem (James Jacobs has, but he is the creative director, not a rules manager—YMMV on his authority here). Ultimately, they may be ignoring the issue because whips are nearly unusable and so it probably shouldn’t ever come up.

Answer 3

You could take the route that increasing or decreasing the size of a whip alters is reach in 5 foot increments. This, a small who has 10 foot reach, large has 20 for, etc. It makes the whip stats on the balor fit, makes size small matter, gives tiny creatures a viable (sort of) reach weapon, etc. Given I've never seen a consistent ruling on whips, it's as good an option as any, I think.