Can a player character that has his arms chopped off still cast spells?
Note: Follow up to this question
Role-playing Games Stack Exchange is a question and answer site for gamemasters and players of tabletop, paper-and-pencil role-playing games. It only takes a minute to sign up.Sign up to join this community
It's not just a flesh wound. The core rules on Pathfinder's magic system specify the default requirements for casting spells with somatic components:
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.
These rules were originally intended for humanoids and other creatures with at least one hand. This restriction doesn't apply to other types of creatures, as answered in the previous question. Their bodies are different, and so they have other means of producing "precise movement."
Unfortunately, this isn't the case for humanoids who formerly had arms and hands. When they lose the ability to perform precise movements, such as when they are pinned, they effectively lose access to that hand. This condition prevents them from casting spells with somatic components. A caster with the Still Spell metamagic feat can cast without somatic spell components, although the +1 spell level increase may put them at even more of a disadvantage.
*Footnote: There is third-party material with rules for lost limbs, which state that a spellcaster can perform somatic components with a mostly-missing arm, but they must pass a potentially difficult caster level check to succeed. As third-party rules, they are not part of the core rules-as-written.
The official Paizo material for the Skull and Shackles adventure path introduces an optional rule system for prostheses for amputated limbs. The closest mention to this issue is in regards to hook hands, which let you perform routine activities. For a spellcaster, performing a somatic component under normal circumstances is "routine", so this should not be a problem.
However, if the whole arm is prosthetic, then it's unclear. The Pirates of the Inner Sea book (also Paizo) says the following about prostheses:
People who lose hands, arms, legs, or feet in combat sometimes replace them with prostheses: realistic simulations of their missing limbs. Usually carved of wood and painted to match the wearer’s skin tone, these items have limited functionality, allowing a person missing a leg to walk at half speed, or enabling a person missing an arm to hold a shield in a fixed position, but little more.
At this point, it's up to the GM. "Limited functionality" can be interpreted in different ways to have varying implication. It's up to the GM whether the caster with a prosthetic arm can flail and wiggle the limb accurately enough to constitute as proper somatic components.
Without arms, you can cast spells without somatic, material, focus and divine focus components. You can also cast spells that normally have somatic components (the vast majority of spells)... by taking the Still Spell feat (cost 1), using a higher-grade spell slot (cost 2), and increasing the casting time if you're able to cast any spell you know rather than preparing your spells in advance (potential cost +1). To cast the many spells with material components, you can also take the Eschew Materials feat (cost 3) to ignore material components worth 1 GP or less. You still won't be able to provide focus components, divine focus components, or costly material components (cost 4), especially if you have no means of preparing your spells (potential cost +2), such as being unable to open any spellbooks you might have (implied).
It's a huge hit to your power, but that's what you get for being placed in a situation that chops off your arms.