Can a spellcaster (learn to) cast while polymorphed into non-humanoid form capable of spellcasting?

Question

Some non-humanoid creatures, for example the naga guardian, are capable of spellcasting (either innately or via class levels) despite not apparently being to provide the normal somatic component of having a hand free (since they have no hands). Others instead are incapable of speech and yet can cast spells with verbal components.

If a typical spellcasting humanoid character is polymorphed (or polymorphs herself) into one of these forms, is she able to mimic that race's ability to provide somatic/verbal components that their form apparently lacks the ability to produce normally? If the answer is no by default, is there any for a way for a character to learn a race's spellcasting style so they can cast while polymorphed into that race? Note that this is not about learning to cast spells without needing somatic/verbal components while in humanoid form.

Answer 1

No study is required

If you polymorph into another race and that race is capable of spellcasting, then you are also capable of spellcasting. From the Transmutation (Polymorph) spell school rules:

While in such a form, you cannot cast any spells that require material components (unless you have the Eschew Materials or Natural Spell feat), and can only cast spells with somatic or verbal components if the form you choose has the capability to make such movements or speak, such as a dragon.

On the example, a dragon can speak and provide somatic components for spells, so changing into a dragon will allow you to cast spells normally.

Note that Somatic components, in general, require a hand:

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.

That is not true for every creature, as they can provide somatic components with other parts of their bodies if they lack hands. At least, that is the intent of the designers. The Magic rules were written considering the characters are all humanoid, which usually have two hands. But when taking monsters into consideration, some rules will be different and exceptions will show up.

For humanoids, somatic components include hand gestures. For things with other shaped bodies, somatic components include whatever gestures their body naturally makes, be that paw or leg movements, tail wagging, squirming bodies, or whatever.

That said, the spellcasting technique cannot be learned from one creature to another, because the members required will be different from your form. How would you cast spells using your tentacles if your form does not have tentacles?

But whenever you are polymorphing into another creature, you innately can use all your spells if that creature type is known for being able to cast spells. If the creature normally cannot cast spells (like animals), then you might need the Natural Spell and/or Wild Speech feats, which is (as far as I know) exclusive to druid characters. Otherwise, it's impossible to cast spells on this new form, as described under the Transmutation (Polymorph) rules.

Answer 2

No, and here's why:

Ultimately, it plays up to the in-house rules of the GM. When Polymorphed (or Shapeshifted), as mentioned above by a previous user, you essentially are that creature, endowing yourself with all the inabilities/abilities it possesses. As an in-house rule I would say no to learning the spell before becoming the creature (GMing a few campaigns myself). The implications are pretty staggering if you consider that simply because - let's say as a dragon - you learned to fire-breathe because it is inherent in that creature, that is by no means grounds to keep it when you shift back to being whatever race you were. I would have to wager Magic/Spells are the same way. Creatures may feel Spells and Magic vs. thinking of them as academically as the other races do, hence their innate ability to alter or skip components in some cases. Sorcerers are much more adept at it and "feel" magic a bit more as well, but ultimately academia is the way they hone their craft.

TL;DR I would say while in that form, yes you may cast those spells, but outside of that "learning" another race's spells could require intense study, if possible at all.