D&D 5E Can you still cast spells while polymorphed/true polymorphed?

[airwalkrr]

The spells would seem to imply both no and yes. On the one hand it says your statistics are replaced with those of the new form, leading me to believe you lose any of your own spellcasting ability and gain spellcasting of the new form. On the other it mentions that you cannot cast spells if the new form lacks a mouth, hands, etc., leading me to believe that you retain spellcasting ability (otherwise why would this even be necessary)? Then there's the thorny issue of "I polymorph myself into the form of the party cleric to dole out extra healing." Such absurdities lead me to believe spellcasting was not intended to be included in the term "statistics," so what does "statistics" include? Is it just the ability scores and form? Does it include resistances and vulnerabilities? Special attacks like breath weapons? E.g. could I polymorph into a fire-breathing dragon whose CR is equal to or lower than my level, or would I lack the ability to breathe fire?

Sorry if these seem like noob questions. I am only a couple months into actually playing 5e with my group.

 

[Gilladian]

In my opinion, not having gone back and carefully read the spells, I would say that if a person takes on a form with digits and vocal cords, he or she can still cast his or her normal spells. No additional spells, no spells that the form would be able to cast. Just like the polymorphed person gains the movement of the new creature (i.e. flight if they have wings) but not the supernatural or extraordinary abilities (no breath weapon, no petrifying gaze, no paralyzing touch). So no, you cannot become a cleric and cast spells as a cleric. You become a humanoid who LOOKS like that cleric, and may sound like him, etc... but cannot cast his spells.

 

[Sunseeker]

If you can satisfy the requirements of the spell, yes. IE: wiggle your fingers properly and speak the magic code-words, then yes.

You DO NOT gain the spellcasting abilities of the creature, only it's physical form. So you could pose as the party cleric to ruin his reputation at home, but you couldn't start casting divine spells.

 

[DaveDash]

I'm pretty certain that you basically put aside your character sheet and take the stat block of the monster you've changed into, you most certainly cannot cast your own spells.

You have the wording wrong for polymorph, it basically says you flat out cannot cast spells OR take any other action that requires hands or speech. Polymorph is limited to beasts, and beasts cannot cast spells.
True Polymorph is a little more loosely worded, and if you true polymorph into something that can cast spells naturally, you gain its ability to cast spells (not your own).

If you polymorphed into a T-Rex, you put aside your character sheet and take the stat block for the T-Rex. That is now your character.
If you True Polymorphed into an Adult Red Dragon, you put aside your character sheet and take the stat block for the Adult Red Dragon. If that Dragon was a spellcasting variant, then you'd be able to cast it's spells.

Shapechange *I think* lets you cast your own spells as the new form, although it's a bit ambiguous, provided that your new form is capable of speech, hand motions, and such.