perform/deception and spells

[Desamir]

More-over, the exact same spell can be cast by two creatures in drastically different ways:

"Most spells require the chanting of mystic words. The words themselves aren't the source of the spell's power; rather, the particular combination of sounds, with specific pitch and resonance, sets the threads of magic in motion." (PHB 203)

The quote contradicts your statement. "The particular combination of sounds, with specific pitch and resonance" means that any given spell with verbal components requires a specific pattern of sounds to cast.

[djreynolds]

Seeing the other thread about trickster clerics and counterspell got me thinking...

Would anyone allow a deception or perform check to bluff casting a spell to draw out counterspells and other reactions?

Yes I love that idea, skills in combat. I let players use them all the time

More idea you got the better.

I let a valor bard spin his sword, performance vs insight, and for the rest of the turn everyone else got advantage, and the enemy was dazed... like a cool hypnotic wave

[Unoriginal]

"Copying a spell into your spellbook involves reproducing the basic form of the spell, then deciphering the unique system of notation used by the wizard who wrote il. You must practice the spell until you understand the sounds or gestures required, then transcribe it into your spellbook using your own notation."

So it seems that the gestures and sounds really are dependent on the spell

[Zorku]

Nah, by raw it clearly falls under this:

Spoiler: PHB175

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V a r i a n t : S k i l l s w i t h D i f f e r e n t A b i l i t i e s
Normally, your proficiency in a skill applies only to a
specific kind of ability check. Proficiency in Athletics,
for example, usually applies to Strength checks. In som e
situations, though, your proficiency might reasonably
apply to a different kind of check. In such cases, the DM
might ask for a check using an unusual com bination of
ability and skill, or you might ask your DM if you can
apply a proficiency to a different check. For example,
if you have to swim from an offshore island to the
mainland, your DM might call for a Constitution check
to see if you have the stamina to make it that far. In this
case, your DM might allow you to apply your proficiency
in Athletics and ask for a Constitution (Athletics) check.
S o if you’re proficient in Athletics, you apply your
proficiency bonus to the Constitution check just as you
would normally do for a Strength (Athletics) check.
Similarly, when your half-orc barbarian uses a display
of raw strength to intimidate an enemy, your DM might
ask for a Strength (Intimidation) check, even though
Intimidation is normally associated with Charisma.

The "action economy" could be covered within RAW too:

Spoiler: same page

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Pa s s iv e C h e c k s
A passive check is a special kind of ability check that
doesn’t involve any die rolls. Such a check can represent
the average result for a task done repeatedly, such as
searching for secret doors over and over again, or can
be used when the DM wants to secretly determine
whether the characters succeed at som ething without
rolling dice, such as noticing a hidden monster.
Here’s how to determine a character’s total for a
passive check:

10 + all modifiers that normally apply to the check
If the character has advantage on the check, add 5. For
disadvantage, subtract 5. The game refers to a passive
check total as a score.
For example, if a 1st-level character has a W isdom of
15 and proficiency in Perception, he or she has a passive
W isdom (Perception) score of 14.
The rules on hiding in the “Dexterity” section below
rely on passive checks, as do the exploration rules
in chapter 8.

5th is a lot more flexible than older versions. it doesn't need a specific way to do it because there are lots of reasonably ways to identify a spell being cast.

I don't follow exactly what connections you're drawing here.

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Taking the subtle spell metamagic into account, any ways of recognizing that someone is casting a spell, other than VSM components, exist by DM fiat (a glowing aura is hardly subtle, but there's some wiggle room if you can perform the mental contortion required to come up with some other reason to call this 'subtle' instead of 'unrestrained.')

By my own sensibilities there's a good deal of variation between both caster and spell type, in terms of exactly what kind of magical -stuff- gets kicked up into the air (maybe some glowing lines left behind by the caster's fingers, or just that atmospheric pressure thing that everyone in fightan' anime seems able to sense,) so for particularly flashy casters you're probably not gonna falsely convince somebody that you're casting a big spell just by miming it, but having any of the prestidigitation and minor illusion type cantrips would convince me that the caster can pretty much replicate enough effects to make this worth rolling a deception check. For sneakier types, especially anybody that performs assassinations or otherwise takes contracts involving subterfuge and/or misdirection, I'd expect very muted magical displays, if any, so putting on your striped shirt and playing pantomime should be enough there. Your standard mage that participates in duels or anything like warfare probably has a few arcane tells that show a spell is coming, but nothing over the top, and that whole ordeal is rather fast paced anyway so the absence of those effects wouldn't be an enormous indication that no magic was happening, save for those who can feel the arcane plucking at the weave, but that's easily achieved by casting a cantrip. You've got some leeway in how strong you expect that arcane sense to be, but because you've got to cast detect magic to recognize stuff that's already in effect I expect it to be pretty weak overall.

I rather like the idea of this all coming together as an improvised action, so for balance purposes I'm inclined to say that casters can recognize what spell is being cast, and if they don't know the spell directly they can tell how big it is (plus I feel cheated when other DMs hit me with some strange description of magic missile where I'm forced to guess if casting shield will get me out of a fairly big hit.) As an improvised action we can take a little bit of everything in order to override that kind of knowledge with an effect that's close enough to fool the enemy caster. This takes a dice roll and eats up action economy so I'm probably going to be happy with the effect it has on combat, but it doesn't make every combat a pain in the ass to resolve, with DM and character hiding what spells they are casting from each other until people declare how they react (which is way more new-ish player friendly than when I see people running it like that,) and we've established lots of little moving parts that can be leveraged to break this tactic if it becomes too dominant in combat, for unforseen reasons.

[Vogonjeltz]

The question is: does counterspell stop the spell from being cast at all, or does it unweave it in the process of resolving? Visually I like the idea of it fizzling the Fireball before it detonates and the like... which would imply someone might 'see what is coming' for a quick counterspell

Well, the spell is used, so technically I suppose it fizzles before it can take effect.

Now, it is still up to individual DMs, but with an arcana check (say, Spell Level +12?) I'd say that someone could identify the spell being used.

I agree, I'm only saying it's not a game rule to allow it, but a personal DM choice. (I expect that difference gets lost sometimes in arguing that point).

The quote contradicts your statement. "The particular combination of sounds, with specific pitch and resonance" means that any given spell with verbal components requires a specific pattern of sounds to cast.

I disagree, it specifies that it's not the words being used, so you could say Abracadabra and I could say Bibbity Bobbity Boo...and we'd get the exact same spell result so long as how we say those words is correct for the spell.

It's not what we're saying, which is the most obvious thing to any observer, but the method of saying it. Now, if you had someone with perfect pitch I suppose they could recognize an exact patter on the fly...but that is insanely rare.

[Naanomi]

Well, the spell is used, so technically I suppose it fizzles before it can take effect

What I meant was we can look at the counterspell process in two ways:

1) I see someone start talking funny and wiggling their fingers, I cast counterspell and their process crumbles; wasting the Spell energy for their upcoming Fireball with nothing happening at all

2) Someone throws a tiny Fireball across the battlefield, and moments before it bursts I cast counterspell and the ball of fire bursts into harmless sparks instead of a massive explosion

The spell (particularly the range limitations) make me think (1) is more likely the 5e counterspell mechanics, I'm just saying that (2) looks cooler and fits the classic 'wizard duel' visuals more; and would give more reason to suspect that recognizing the spell is a reasonable idea (though 'faking spell casting' it probably easier with (1))

[Desamir]

It's not what we're saying, which is the most obvious thing to any observer, but the method of saying it. Now, if you had someone with perfect pitch I suppose they could recognize an exact patter on the fly...but that is insanely rare.

You wouldn't need perfect pitch, you'd just need the ability to recognize a tune or a rhythm. To continue the music analogy, if you know how to cast the spell yourself, you know how to "play the tune" and you'd easily recognize someone else playing the same melody.

Same thing if the spell has somatic components--if it's perceptible, you may be able to recognize it.

To clarify, I'm not saying this is supported or refuted by anything in the game rules, I'm just suggesting that it's plausible from an in-world perspective.