How does a light shield impact your ability to cast spells with a somatic component?

Question

Im trying to understand the somatic component of spellcasting, in pathfinder, and how it relates to shields. The core rule book has this to say about bucklers:

You can cast a spell with somatic components using your shield arm, but you lose the buckler’s AC bonus until your next turn.

This about a light shield:

A light shield’s weight lets you carry other items in that hand, although you cannot use weapons with it.

And this about heavy shields:

A heavy shield is so heavy that you can’t use your shield hand for anything else.

Assuming all your other hands are otherwise unavailable, this seems clear that you can cast spells that have a somatic component while wearing a buckler and cannot while wearing a heavy shield. However, the rules don't seem as clear about light shields. How does a light shield impact your ability to cast spells with a somatic component?

Answer 1

Light shields prevent you from using that hand for spellcasting.

Each entry there tells you what you can do with that hand when a shield is equipped on that arm/hand:

Buckler: Anything, including casting spells (but with some consequences).
Light shield: Hold items.
Heavy shield: Nothing at all.

Light shields let you hold items in that hand that aren't weapons, and that's it. Spellcasting doesn't qualify.

Answer 2

You cannot provide somatic components with a light shield

As opposed to his previous comment on the subject, here is another (direct) claim from James Jacobs (Paizo's Creative Director) that you cannot use a light shield's arm to provide somatic components. So, while his first statement may have been right by 2010, either JJ changed his stance on the subject, or simply changed his mind and that previous statement is no longer valid from 2013 and on (I checked all of his posts mentioning "light shield").

Can a Cleric wielding a light shield on each arm cast spells with somatic components?

Nope. That's what bucklers are for.

Alternatively, they released the Shielded Mage feat on the Armor Master's Handbook, which fixes that exact problem:

You have learned how to cast spells from behind the safety of a shield.

Prerequisites: Shield Focus, base attack bonus +3 or fighter level 1st.

Benefit: You reduce the arcane spell failure of any shield you use by 15% (to a minimum of 0%). Using a shield does not prevent you from completing somatic spell components with the hand wielding the shield.

Note that the feat doesn't mention the type of shield it grants it's benefit to, meaning that you may even cast spells holding a heavy shield if you take the feat.

Answer 3

You cannot use a hand holding a shield to perform somatic components. The buckler is a specific exception which states that you can cast a spell while holding it and lose the shield bonus to AC.

In any other case, you fall back on the following rules (emphasis mine):

A somatic component is a measured and precise movement of the hand. You must have at least one hand free to provide a somatic component.

You need a free hand to cast, and a hand holding a shield is not free.

Strapping a shield to your arm to gain its shield bonus to your AC, or unstrapping and dropping a shield so you can use your shield hand for another purpose, requires a move action.

Since your hand is not free, you can't use it for anything unless specifically stated. This means using a weapon or casting a spell for a buckler, carrying an object for a light shield, and nothing for a heavy shield.

Answer 4

James Jacobs (Paizo Creative Director) has declared that light shields leave the hand they are equipped in free for spellcasting. The silly juggling maneuver is no longer necessary, but this does make bucklers all but pointless for spellcasters.

From his post:

A light shield allows spellcasters to use their hand to cast, and lets you carry an object; the only thing it actually prevents is wielding a weapon.

Answer 5

The wording is ambiguous, and anyone claiming any one answer as the actual correct answer is overstating their claim.

The light shield says it can hold things, but cannot wield weapons. The basic rules for shields don’t cover the subject in a general way; what you can and can’t do with a shield in your hand is left up to the individual shield’s description—in this case, that you can hold things, but cannot wield weapons. Anything that isn’t one of those two things, isn’t covered. We don’t know whether or not it should be allowed. Are somatic components more like just carrying things, or more like wielding a weapon? Actually, they’re pretty unlike either of those things.

So it could go either way, and the rules, as written, do not tell us. A GM has to make a ruling. In a notable case, Paizo’s creative director, James Jacobs, thinks somatic components should be allowed with a light shield, which could be an argument that this was the intent. But he also hedged that claim a lot (“I believe...”), and in any event he’s the creative director and not a rules authority—he’s been known to get the rules wrong all the time. So, by his own admission, he’s not as strong an authority on this subject as you might expect based on his employment at Paizo.

Answer 6

The absolute best answer is Creative Director James Jacobs' response on the Paizo.com forums:

Switching a held object from one hand to the other doesn't require an action, so the end result is the same whether or not you use the light shield hand to lay on hands or your weapon hand after switching your weapon to the off hand, and then back to your weapon hand.

The fact that allowing you to use your light shield hand to do so without so many fiddly steps is why I'd say it's fine to let it work that way.