Is it possible to benefit from multiple Shield spells?

Question

The Shield Spell allows you to use the Shield Block reaction, which ends the spell and prevents you from casting it again for 10 minutes. But what if you know the Shield spell from multiple different features? For example, An Elf might know Shield as an Innate spell from Otherworldly Magic, while also having it as a prepared Wizard spell, while also learning it a third time when he takes the Sorcerer Dedication feat. Furthermore, I don't see anything that would stop him from preparing the same cantrip multiple times with his Wizard cantrip slots, so he could conceivably have five Shield spells prepared as Wizard Cantrips.

If this character uses Shield Block, preventing him from casting Shield again for 10 minutes, does this prevent him from casting any of his Shield spells, or does it only prevent him from using that one Shield spell?

Answer 1

No.

Shield says

After you use Shield Block, the spell ends and you can't cast it again for 10 minutes.

It does not say you can't cast a specific variety of Shield again, or that you can't cast that slot of Shield again. It says the spell (Shield) ends, and you can't cast it (Shield) again. There's not any qualifier on that statement, simply "use Shield Block, you can't cast Shield for 10 minutes".

Which is fair - as a spellcaster using cantrip slots, using Shield is cheap from an investment perspective. Yeah, you've gone the extra mile with the extra cantrip slots, but they're not necessary. Combats in Pathfinder 2e are expected to last around 4-6 rounds. Even if you didn't go the extra mile, if you could prepare 5 cantrips of Shield and cycle them, you're effectively giving yourself 5-25 temporary hp every round, and you're pretty likely to not run out. Additionally, your shield has the roughly same hardness as the top-of-the-line Sturdy Shield for a given level, but since you're casting it you don't have to worry about the shield's hardness or BT - you'll always get the best benefit if you can cast it, without ever needing to worry about repairs.

If you want to use a shield, however, there's nothing stopping you from actually picking up a real shield. Verbal and Somatic Casting Actions don't need a free hand, and there's no such thing as shield proficiency (though you may want to invest in Shield Block as a General Feat) or spell failure for using one. You could also hold a physical shield and just cast the Shield spell until you actually have to use its block, then switch to raising your physical shield.

Answer 2

The rule for this is in a rather obscure place in the book (the sidebar, pg 444 of the Core Rulebook), but unfortunately means no. And this applies to all duplicate effects

(Emphasis mine)

Duplicate Effects

When you’re affected by the same thing multiple times, only one instance applies, using the higher level of the effects, or the newer effect if the two are the same level. For example, if you were using mage armor and then cast it again, you’d still benefit from only one casting of that spell. Casting a spell again on the same target might get you a better duration or effect if it were cast at a higher level the second time, but otherwise doing so gives you no advantage.

Since it is a personal targetted spell you can't gain it by casting afterwards, you might be able to get it by activating an item, but I'm yet to find a case that isn't a Cast a Spell action, which would fall under the effects of the Shield spell preventing you from casting it again, regardless of origins.

Answer 3

It's unclear, but I would say yes, you can benefit from multiple copies of Shield (with some caveats).

As you've pointed out, if you play an Elf Wizard who takes the Otherworldly Magic and Sorcerer Dedication feats (taking the Draconic bloodline or any other one with arcane as its spell list), you can have Shield as your OM cantrip, both SD cantrips, and you can prepare Shield as all of your cantrips for the day if you wish.

Determining whether casting one copy of Shield prevents you from casting the others after using the Shield Block reaction is difficult as Shield is the only spell in the list that has the "can't cast again for X minutes" restriction and there's little precedent for this situation that I've been able to see, but consider that preparing multiple copies of a levelled spell allows you to cast that spell in its entirety once for every copy you have prepared on a given day, treating each copy as its own distinct spell. Now let's look at the wording of the Shield spell:

You raise a magical shield of force. This counts as using the Raise a Shield action, giving you a +1 circumstance bonus to AC until the start of your next turn, but it doesn't require a hand to use.

While the spell is in effect, you can use the Shield Block reaction with your magic shield. The shield has Hardness 5. After you use Shield Block, the spell ends and you can't cast it again for 10 minutes. Unlike a normal Shield Block, you can use the spell's reaction against the magic missile spell.

I would say "the spell" and "it" refer only to that specific copy of Shield, and that each one would have its own 10 minute timer after the reaction is used. I unfortunately can't back this up with a passage from the rulebook because there's nothing in there about whether multiple copies of a spell are considered the same spell for this purpose, but I'd point out that if you have multiple copies of the same buff spell on one target (Wind Walk for example), Dispel Magic only removes one copy of it even though it ends "one ongoing spell" indicating that each copy is considered separately and the same should apply for Shield.

As Isaac pointed out, the AC bonus wouldn't stack regardless since it's a Circumstance bonus and typed bonuses only apply the highest of those active, and you'd only get to use Shield Block once per round assuming you hadn't used your reaction for anything else, until you'd used it once for each copy of Shield you cast.