If a spell has verbal and/or somatic components, are they absolutely vital for its casting?
Let me give a clear example: suppose a wizard is trying to cast Detect Magic on a creature they are speaking to, but they don't want the creature to notice the spell is being cast. Detect Magic has both verbal and somatic components, so the wizard might comply with the somatic portion by just forcefully gesticulating as one would in an energetic conversation. But they might not be able to actually speak out the proper incantations.
Another situation: a sorcerer has both her hands tied behind her back and is trying to cast Acid Splash. She can't perform the somatic portion of the spell, but she can easily speak out the incantations.
In these situations, can the spells simply not be cast? Or can the spells still be cast, but with some kind of penalties added? And if the answer is the latter, which penalties should I consider?