What ways are there to disrupt spellcasting in 5e?

[CorporateSlave]

The whole ‘fail with a CON’ save is an unnecessary piece of this... *if* you are allowed to use your readied action to go ‘mid-cast’ or even (in most cases) ‘before casting begins’; things like Stunning Fist can come into play without the creation of new mechanics

Indeed, I probably should have written "Concentration check," since that is how/why spells fail in 5e. I was just thinking of what a Concentration check is mechanically.

[ThePolarBear]

The problem you guys are having is you are ignoring what each other is saying. The trigger the other side is using is not 'casting a spell'; it is 'starts to cast a spell'.

Sorry, what?

The quote from the post i replied to:

Some posters have claimed that the if trigger for the Reaction is "that guy casts a spell", then the Reaction can't happen until the spell casting has finished.

If the trigger is "that guy casts a spell", then "that guy casts a spell" has to finish, right? When does it finish?

Start is a valid trigger unless the DM decides otherwise

If it is, please, tell me what is perceivable about "start". I'm all ears. Because without contextualizing what is starting, you are NEVER going to provide anything that is perceivable. We can conceptualize it, but again, the request is for something that is perceivable, not a conceptualization. The trigger at that point is the actual, perceivable occurrence that is linked to what "start" means in context. Because THAT is the perceivable occurrence.

I UNDERSTAND that for someone "starting" is a valid trigger. Not a single person has, however, moved on the next step - except me in the example of the race.
And again, i've stated, before ANY rebuttal, that things like "goes for the purse" or "chants weird sounds" are valid triggers. But you'll have to agree that neither really encapsulates in and of itself what "starting to cast a spell" can mean: i can start chanting before going for the purse: if the trigger is "goes for the purse", the spell is well underway the process of being cast at that point.
It doesn't help that we do not have a common ground based on factual experience for casting a spell, so we can't really conceptualize it as well as other things.
And this compounds further on with other rules (or lack thereof) on how to deal with the resulting situation. For how it is, even if you were to dislodge a material component from the hands of someone... there is something that prevents simply picking it back up and continuing? What if that material component was not even needed?

[Naanomi]

Indeed, I probably should have written "Concentration check," since that is how/why spells fail in 5e.

Even that seems to be a whole separate issue, inventing a disruption mechanic at all... when existing mechanics can disrupt spells already *if* the timing issue is addressed. You have to decide the timing possibilities of Readied Action before the merits of a disruption houserule even becomes a possibility

[jh12]

Or to come at this from a less aggravated place, in order for me to answer the core question of this thread, I need information that 5e intentionally does not provide. Maybe others are happy to answer from "the rules" as their only basis, in a vacuum, but I am not.

Does it bother you that a character can make the same number of attacks in a turn, regardless of whether they are swinging a polearm at someone 10 feet way from them or thrusting a dagger at someone standing right next to them?

[CorporateSlave]

Even that seems to be a whole separate issue, inventing a disruption mechanic at all... when existing mechanics can disrupt spells already *if* the timing issue is addressed. You have to decide the timing possibilities of Readied Action before the merits of a disruption houserule even becomes a possibility

Except in RAW the timing issue is already addressed. It has been removed, and is not relevant. (Remember back in AD&D 2e? Casters had to stay off the line because any little old hit would disrupt their spell as it was being cast, because it took a specific duration that was interruptible by the game mechanics as written (1 Round spells took the full round, anything else that happened during that round could disrupt them while being cast). That's gone in 5e. Just like spell failure while wearing armor - now you just need to be proficient. Just like not being able to move (or limiting to 5' of movement) while casting - now you still get full movement.)

Some people are insisting timing must still be relevant because (presumably) they miss this feature of older editions, and it makes more sense to them. But 5e only makes timing relevant when it comes to spells with a casting time longer than 1 Action in Combat.

Timing matters? Counterspell works just as well against a 1 Action casting time spell as it does against a 1 Reaction ("fraction of a second") spell...like another Counterspell. Such differences in timing! Omitted from the RAW in favor of just having the desired in game effects.

[CorporateSlave]

Does it bother you that a character can make the same number of attacks in a turn, regardless of whether they are swinging a polearm at someone 10 feet way from them or thrusting a dagger at someone standing right next to them?

Yeah, right? Things like this are exactly why I am quite happy to take the rules for what they are...game rules...and not need to insist there must be some five levels deep Inception grade real world practical justification for them. God help you playing chess with that guy! :small wink: I'm just not worried about the specifics of why a werewolf doesn't get cut as badly by a weapon that isn't enchanted magically, or why after just the right Long Rest the Fighter wakes up able to Action Surge and make four attacks when 8 hours ago he used to only be able to make two. It's a game. If you're not happy with the game, there is also something called "real life" you can go out and live. That's way more precise!

[Aimeryan]

Look, if somebody wants to ask JC about this and it ends up in a future SA Compendium as official ruling that "sure, you can ready an Attack for the start of spell casting and possibly interrupt the casting if the caster fails a CON save." then great, that's now the RAW and lets roll with it!

The bolded parts together will not be RAW, although it wouldn't be against RAW for a DM to rule that way. Readying an attack for the start of spell casting will be RAW, but whether or not that does anything but damage is up to the DM. Readying a spell that could possibly interrupt the casting is possible, but I've had difficulty finding useful applications for it (you could just cast the spell on your turn).

I'm not ignoring it (although a lot of what I have written is ignored because there is apparently not a good way to counter it), I'm saying that per the RAW you can make whatever valid trigger you want. You want to say "starting to cast a spell" ok, fine. But since the rules don't break down 1 Action spell casting in that manner, the in game effect will be that the spell will not be interrupted and it will be cast, followed immediately by the effect of your attack (or whatever Readied Action you were using).

The rules don't state actions are atomic. There are also numerous examples where actions can be interrupted in one form or another; counterspell, shield, absorb elements, movement, etc. For spells specifically, counterspell is probably the strongest example of both perceiving spells while occurring and then stopping the casting - and it doesn't even require you to be ready for it.

Since spells don't require concentration to cast (unless longer casting time), damage wont break it (can't break what doesn't exist). A grapple to hold their arms/hands/mouth should be doable, but would require DM ruling.

[Max_Killjoy]

If the trigger is "that guy casts a spell", then "that guy casts a spell" has to finish, right? When does it finish?

Except that that is not the trigger some posters want to use, as you yourself note in the rest of your post. (Furthermore, I'd argue that even "casts a spell" only "necessitates" waiting for the casting to finish because of the contrivance in the rules that Reactions don't happen until the trigger finishes.)

The trigger that they want to use is "starts to cast a spell". At least as described (in the setting/fiction level text at least) in the PHB, casting a spell does take a certain amount of time, involving complex movements and words of some kind for most spells cast by at least some classes.

At the risk of broken record... the unanswered question is, how long does "casting a spell" last (in time, not in "actions") and then whether that's enough time for another character to recognize that the caster started, get off their own attack, and attempt to interrupt the caster before the caster actually finishes the process of casting the spell.

[Spiritchaser]

Yeah, I know, but it is also an opposed athletics check, and skill rules are described in a notoriously limited way. What you can do exactly is up to the table conventions and DM, and I can imagine quite some would allow an opposed athletics when grappling to restrain a targets arms and / or prevent speaking.

Personally (and this is purely a house rule I have), I allow a grappler the opportunity to attempt to disrupt somatic or verbal components of a casting by a grappled target, opposed by the target’s casting stat. I don’t consider this to be a counterspell at all, so the spell is not wasted, just impossible to cast.

This has the effect of making snuggleguts the prodigy Barbarian with expertise in athletics very scary for casters.

It hasn’t actually increased the prevalence of subtle spell, partly because I just don’t use it against players all that much, and not many of my players seem to want to play a sorcerer.

[Aimeryan]

...please, tell me what is perceivable about "start". I'm all ears. Because without contextualizing what is starting, you are NEVER going to provide anything that is perceivable. We can conceptualize it, but again, the request is for something that is perceivable, not a conceptualization. The trigger at that point is the actual, perceivable occurrence that is linked to what "start" means in context. Because THAT is the perceivable occurrence.

I UNDERSTAND that for someone "starting" is a valid trigger. Not a single person has, however, moved on the next step - except me in the example of the race.
And again, i've stated, before ANY rebuttal, that things like "goes for the purse" or "chants weird sounds" are valid triggers. But you'll have to agree that neither really encapsulates in and of itself what "starting to cast a spell" can mean: i can start chanting before going for the purse: if the trigger is "goes for the purse", the spell is well underway the process of being cast at that point.
It doesn't help that we do not have a common ground based on factual experience for casting a spell, so we can't really conceptualize it as well as other things.
And this compounds further on with other rules (or lack thereof) on how to deal with the resulting situation. For how it is, even if you were to dislodge a material component from the hands of someone... there is something that prevents simply picking it back up and continuing? What if that material component was not even needed?

Ahh, I see what you are having difficulty with. OK, so the ready trigger is for something you perceive, not a universal truth of life. An example:

The situation is you are going into space in a rocket. You can see out of a window.
'I will shout in delight when I have got into space' - the Ready action.
As you rise up you see the atmosphere get fainter and fainter, until you can't see it anymore - you perceive yourself now being in space, the trigger is met, you whoop in glee. The truth is, however, that the Kármán line (the official point at which you get into space) has actually not yet been reached. It doesn't matter, the trigger is what you perceive, not some unperceivable defined point.

For spell casting, this is when your character perceives the spell casting has started - which is up to the DM to narrate.

[Max_Killjoy]

Ahh, I see what you are having difficulty with. OK, so the ready trigger is for something you perceive, not a universal truth of life. An example:

The situation is you are going into space in a rocket. You can see out of a window.
'I will shout in delight when I have got into space' - the Ready action.
As you rise up you see the atmosphere get fainter and fainter, until you can't see it anymore - you perceive yourself now being in space, the trigger is met, you whoop in glee. The truth is, however, that the Kármán line (the official point at which you get into space) has actually not yet been reached. It doesn't matter, the trigger is what you perceive, not some unperceivable defined point.

For spell casting, this is when your character perceives the spell casting has started - which is up to the DM to narrate.

And could very well require a check of some kind to correctly judge when the spell casting starts.

(Which as an aside gives some added "cookie" to characters who study and understand magic despite not being spellcasters... that "ranged Rogue" with the Arcana skill gets to use it.)

[CorporateSlave]

The rules don't state actions are atomic. There are also numerous examples where actions can be interrupted in one form or another; counterspell, shield, absorb elements, movement, etc. For spells specifically, counterspell is probably the strongest example of both perceiving spells while occurring and then stopping the casting - and it doesn't even require you to be ready for it.

Exactly! There are several specific exceptions to the general rule that an Action continues from start to finish. It is apparently very counterintuitive to many people here, but in 5e one of the core philosophies is that spells/abilities/etc can allow you to break general rules of game play. These exceptions do not change the general rules...they function as exceptions on their own.

To put it another way, the fact that by RAW Counterspell can interrupt a spell as it is being cast does not provide any evidence that there is another way to interrupt a spell that is being cast. It only states that Counterspell can do this. That's what "specific beats general" means.

The PHB (and everything else) would have to be a lot longer and wordier if they had to list every way in which something is not doable. They get around this using specific beats general.

The rules don't state Actions are atomic? Well, do they state that Actions are not atomic and always interruptible? No. Do they have a bunch of spells and abilities that allow specific interruptions? Yes. The only Action that the RAW explicitly states is not generally "atomic" is the Attack action, as it states if a PC can make multiple attacks as part of the Attack Action, this can be broken up by movement or interrupted by an OA (if applicable). Movement can be interrupted by RAW, but Movement isn't an Action in 5e.

[PhoenixPhyre]

At the risk of broken record... the unanswered question is, how long does "casting a spell" last (in time, not in "actions") and then whether that's enough time for another character to recognize that the caster started, get off their own attack, and attempt to interrupt the caster before the caster actually finishes the process of casting the spell.

Here's the thing. The only honest answer they could give to that question is "it varies, but significantly less than 6 seconds." Not all spells are the same (even with the same cast time in actions). Not all actions are the same length, even if the action is the same.

You're asking the abstraction to provide information that it intentionally cannot provide. In computer science terms, you're asking for the value of a private class member. If they wanted to give this information, they'd have to rewrite the entire system from ground up, because everything would break. The minimum resolution of the game clock is 1 round, which is approximately 6 seconds. Anything below that is imperceptible from the point of view of the players. And might depend entirely on the situation, the spells, the traditions of the spell caster, the setting's exact take on magic, etc. So not giving an answer to that question is the only honest thing they can do. Anything else would be false and would break the system. Is that unsatisfying to you? Sure. But that doesn't make it wrong. It just means you don't like it.

[CorporateSlave]

At the risk of broken record... the unanswered question is, how long does "casting a spell" last (in time, not in "actions") and then whether that's enough time for another character to recognize that the caster started, get off their own attack, and attempt to interrupt the caster before the caster actually finishes the process of casting the spell.

Also at the risk of broken record...the question is answered, and the answer is; for the sake of simplicity the 5e RAW has omitted the need for specific timing, and unlike earlier editions, does therefore not allow by RAW 1 Action spells to be interrupted except by certain spells or abilities.

I know you don't like that answer because it isn't detailed or realistic enough. Few if any 5e rules are very detailed or realistic...it's a game. If you don't find appealing to the authority of the game rules as a satisfactory answer, perhaps you should be writing a new game rather than playing this one?

[Naanomi]

Real scenario: invisible Shadow Monk is standing within reach of two spellcasters; Combat has begun, and she has won initiative. She doesn’t know if either spell caster will actually join combat, but wants to be ready to stop one of them if possible... so she wants to ready her action to get the jump on either one of they start to cast a spell (with the intent on using stunning fist to stun them).

Second real scenario: The party is escorting a prisoner across hostile territory, he has tried to escape a few times but has been compliant. The party rogue has been tasked with watching over the prisoner. The party is anbushed, the rogue wins initiative, and declares that if the prisoner tries to escape he will knock him unconcious. Escaping the ropes has been determined to only take a single action with a (admittedly difficult) DEX check.

The viability of both is dependant on the answer to the same question: can you respond with a Ready Action when someone attempts an action (or rather, the obvious visual cues of them attempting that action to someone specifically looking for them) but before the action takes place? Independent of specific time an action takes or anything like that, just a simple ‘can a readied Action pre-empt a declared action’ and... if not, what should the players above have done to accomplish their goals?

[Aimeryan]

Exactly! There are several specific exceptions to the general rule that an Action continues from start to finish. It is apparently very counterintuitive to many people here, but in 5e one of the core philosophies is that spells/abilities/etc can allow you to break general rules of game play. These exceptions do not change the general rules...they function as exceptions on their own.

To put it another way, the fact that by RAW Counterspell can interrupt a spell as it is being cast does not provide any evidence that there is another way to interrupt a spell that is being cast. It only states that Counterspell can do this. That's what "specific beats general" means.

The PHB (and everything else) would have to be a lot longer and wordier if they had to list every way in which something is not doable. They get around this using specific beats general.

The rules don't state Actions are atomic? Well, do they state that Actions are not atomic and always interruptible? No. Do they have a bunch of spells and abilities that allow specific interruptions? Yes. The only Action that the RAW explicitly states is not generally "atomic" is the Attack action, as it states if a PC can make multiple attacks as part of the Attack Action, this can be broken up by movement or interrupted by an OA (if applicable). Movement can be interrupted by RAW, but Movement isn't an Action in 5e.

Bolded, agreed. However, that is not what we are discussing. You state there is a general rule that actions are atomic - where? I would love to read it, please. If there is no general rule, how can you require an exception? There is nothing to except.

Counterspell neither requires, nor states, any exception to perceiving that a spell is being cast. You perceive a spell is being cast, you can choose to use Counterspell as a Reaction. The Counterspell then comes in between the opponents Action, thus proving that Actions are divisible - not that we need that proof, since there is no general rule that they are not. Whether or not it succeeds at interrupting the spell is superfluous to what we are discussing.

[Unoriginal]

"Because those are the rules" is never an actual answer, it's just a way to avoid addressing the real questions via an appeal to authority

Try to answer this: why is it forbidden to use your hands in football/soccer unless you're the goalie?

(and an avoidance that 5e seems deliberately built on.)

"The game is the game, not real life, and the DM can rules whatever they wish to rule" are very much some of what 5e is built on, indeed.

Again, feature, not but.

Bolded, agreed. However, that is not what we are discussing. You state there is a general rule that actions are atomic - where? I would love to read it, please. If there is no general rule, how can you require an exception? There is nothing to except.

Counterspell neither requires, nor states, any exception to perceiving that a spell is being cast. You perceive a spell is being cast, you can choose to use Counterspell as a Reaction. The Counterspell then comes in between the opponents Action, thus proving that Actions are divisible - not that we need that proof, since there is no general rule that they are not. Whether or not it succeeds at interrupting the spell is superfluous to what we are discussing.

Actually the Counterspell still comes after the "cast a spell" action.

It comes before the *effects* of the spell, since it blocks them, but the casting is very much completed (as proved by the spell slot being spent and the caster not being able to use their Action to do something else).

[Max_Killjoy]

Also at the risk of broken record...the question is answered, and the answer is; for the sake of simplicity the 5e RAW has omitted the need for specific timing, and unlike earlier editions, does therefore not allow by RAW 1 Action spells to be interrupted except by certain spells or abilities.

I know you don't like that answer because it isn't detailed or realistic enough. Few if any 5e rules are very detailed or realistic...it's a game. If you don't find appealing to the authority of the game rules as a satisfactory answer, perhaps you should be writing a new game rather than playing this one?

That's not an answer to the question, it's a rules-embedded refusal to answer the question.

At least I can point to this thread the next time some nitwit tries to claim that D&D is a "simulationist" system, which it never has been in any way.


(As for why I'm caught up in 5e discussion, as part of helping someone else with a project, I was asked to familiarize myself with 5e, with the reassurance that "a lot of the stuff that bugged you about D&D is gone"... which turns out to not be the case. I have not played any version of D&D since the mid 90s, and then washed my hands of the whole thing after reading the 3.whateveritwas PHB.)

[NaughtyTiger]

Try to answer this: why is it forbidden to use your hands in football/soccer unless you're the goalie?

wait, wait, I got this... Foot is in the name of the game!!! Handball is a completely different sport!!! yay me, i got one right!

@ProsecutorGodot, doesn't count cuz I am not weighing in the actual absurd discussion.

[Unoriginal]

That's not an answer to the question, it's a rules-embedded refusal to answer the question.

At least I can point to this thread the next time some nitwit tries to claim that D&D is a "simulationist" system, which it never has been in any way.

You're the one asking for a simulationist answer, though.

Also, it can be argued that D&D 3.X tried to be a simulationist system, at least to an extent. Didn't work out well.

4e and 5e did away with that idea entirely.

(As for why I'm caught up in 5e discussion, as part of helping someone else with a project, I was asked to familiarize myself with 5e, with the reassurance that "a lot of the stuff that bugged you about D&D is gone"... which turns out to not be the case. I have not played any version of D&D since the mid 90s, and then washed my hands of the whole thing after reading the 3.whateveritwas PHB.)

Well, I'm sorry you ended up not liking 5e. I hope you find systems you like more, if you don't have some already.

[ProsecutorGodot]

wait, wait, I got this... Foot is in the name of the game!!! Handball is a completely different sport!!! yay me, i got one right!

@ProsecutorGodot, doesn't count cuz I am not weighing in the actual absurd discussion.

I'm not judging, just watching with popcorn in hand at this point.

[Max_Killjoy]

Try to answer this: why is it forbidden to use your hands in football/soccer unless you're the goalie?

The generally agreed-upon answer there is that it was an attempt to make the game safer (and more socially/legally accepted), as previously the ball could be handled or carried, and players would go to extreme lengths to dislodge the ball. Other variations of "football" -- see rugby, American "gridiron", etc -- all developed different ways of addressing this question over time.

"The game is the game, not real life, and the DM can rules whatever they wish to rule" are very much some of what 5e is built on, indeed.

Again, feature, not but.

"It's a game, not real life" is just more evasiveness, treating a basic fact as if it were a strong justification. Of course it's not real life, but it's also not just an abstract set of arbitrary rules. There IS a fiction/setting layer that matters -- or why would we be playing an RPG at all? Without that setting/fiction layer, there's no role to play to begin with.

Is this a board game, or an RPG? What is the actual purpose of the rules? What happens when the rules produce results that would be fine in an abstract board game, but fail to maintain the believable connection between in-setting/fiction events and their outcomes that's crucial to an RPG ruleset?

If it only takes about a second to cast a spell, it's going to be hard to interrupt unless you're fully ready to strike.

If it takes the entire 6 seconds of a round to cast a spell, it's going to be very easy to interrupt if you have the movement or range to hit them inside that timeframe.

[Aimeryan]

Actually the Counterspell still comes after the "cast a spell" action.

It comes before the *effects* of the spell, since it blocks them, but the casting is very much completed (as proved by the spell slot being spent and the caster not being able to use their Action to do something else).

That is quite the fiction you have created! Lets check the spell shall we?

Casting Time: 1 reaction, which you take when you see a creature within 60 feet of you casting a spell

You attempt to interrupt a creature in the process of casting a spell. If the creature is casting a spell of 3rd level or lower, its spell fails and has no effect. If it is casting a spell of 4th level or higher, make an ability check using your spellcasting ability. The DC equals 10 + the spell's level. On a success, the creature's spell fails and has no effect.

[Unoriginal]

The generally agreed-upon answer there is that it was an attempt to make the game safer (and more socially/legally accepted), as previously the ball could be handled or carried, and players would go to extreme lengths to dislodge the ball. Other variations of "football" -- see rugby, American "gridiron", etc -- all developed different ways of addressing this question over time.

And if a non-goalie player where to use their hands in soccer, it would be against the rules, yes?



[QUOTE=Max_Killjoy;23800014]
"It's a game, not real life" is just more evasiveness, treating a basic fact as if it were a strong justification. Of course it's not real life, but it's also not just an abstract set of arbitrary rules. [QUOTE=Max_Killjoy;23800014]

It's not abstract, but it is utterly arbitrary.

There IS a fiction/setting layer that matters -- or why would we be playing an RPG at all? Without that setting/fiction layer, there's no role to play to begin with.

And that setting/fiction is just as arbitrary. Why do wizards need a spellbook to learn new spells? Why do Illithids have psychic powers rather than magic? Why is a CR 12 Warlord legendary?

All is arbitrary.

[QUOTE=Max_Killjoy;23800014] What is the actual purpose of the rules?[QUOTE=Max_Killjoy;23800014]

To be able to play a roleplaying game.

What happens when the rules produce results that would be fine in an abstract board game, but fail to maintain the believable connection between in-setting/fiction events and their outcomes that's crucial to an RPG ruleset?

The arbiter, aka the DM, decides of a different version that is more believable to the people involved.

If it only takes about a second to cast a spell, it's going to be hard to interrupt unless you're fully ready to strike.

If it takes the entire 6 seconds of a round to cast a spell, it's going to be very easy to interrupt if you have the movement or range to hit them inside that timeframe.

A spell without a several-rounds-casting-times takes a fraction of a turn to cast, and a turn is what happen within a 6 seconds round from the near-simultaneous viewpoint of the characters depending on the initiative order.

In other terms, it's fast enough that it can't be interrupted.

That is quite the fiction you have created! Lets check the spell shall we?

Nice way to try to accuse me of lying, but:

its spell fails and has no effect
[...]

On a success, the creature's spell fails and has no effect.

It does not say "the creature's spell is blocked mid-way and they don't spend their spell slots", does it?

Counterspell makes the spell ineffective. It doesn't strangle the caster to make them stop or the like.

The spell is cast. It just fails because of the Counterspell.

Now, it's quite true that the casting of Counterspell occures within the time of the process of casting the other spell, but it being simultaneous doesn't mean it's divisible.

[patchyman]

It really isn't. It's more on what a Ready Action requires, what start means, and apply it to casting.

For you, what does "start casting" mean? When does someone start casting?

First sound out of their mouth would fit the criterion if you are arguing in good faith.

[NaughtyTiger]

Nice way to try to accuse me of lying, but:

now now, let's not throw out accusations of "lying" when folks are just trying(?) to suggest you were wrong. the rhetoric is bad enough without accusations.

[JoeJ]

First sound out of their mouth would fit the criterion if you are arguing in good faith.

And at what point have enough sounds been made that an observer could perceive that they are casting a spell rather than speaking? And how is perceiving somebody start to cast a spell different from perceiving somebody casting a spell (assuming that they were not doing so before you started watching them)?

[Max_Killjoy]

And if a non-goalie player where to use their hands in soccer, it would be against the rules, yes?

Depends on the situation, anything from a cardless foul and freekick to the other team, to a redcard and penalty kick to the other team.

But really, that's beside the point -- you appeared to be going for a "no one knows why this rule is this way, it just is" example, when in fact there was a known concrete reason that the rule in question developed originally.

It's not abstract, but it is utterly arbitrary.

Of course it's abstract -- it's not based on what's happening in-fiction, it's purely a rule in a vacuum.

And that setting/fiction is just as arbitrary. Why do wizards need a spellbook to learn new spells? Why do Illithids have psychic powers rather than magic? Why is a CR 12 Warlord legendary?

All is arbitrary.

You're conflating arbitrary with imaginary, or extending "arbitrary" to mean "anything not directly copied/derived from independent real fact".

At least in my worldbuilding, nothing is purely arbitrary, there's always a specific reasoning involved, everything is done to be a cause and/or an effect of some aspect of the setting or the intended story or the intended gameplay.

To be able to play a roleplaying game.

Nice circular tautology.

Doesn't really answer the question, though.

The arbiter, aka the DM, decides of a different version that is more believable to the people involved.

If a rule repeatedly requires the DM to do this, it's broken -- and "the DM can just rule otherwise" is an appeal to the Rule 0 Fallacy.

A spell without a several-rounds-casting-times takes a fraction of a turn to cast, and a turn is what happen within a 6 seconds round from the near-simultaneous viewpoint of the characters depending on the initiative order.

In other terms, it's fast enough that it can't be interrupted.

That's just working backwards from the rule to justify the rule being called into question.

[CorporateSlave]

Bolded, agreed. However, that is not what we are discussing. You state there is a general rule that actions are atomic - where? I would love to read it, please. If there is no general rule, how can you require an exception? There is nothing to except.

Counterspell neither requires, nor states, any exception to perceiving that a spell is being cast. You perceive a spell is being cast, you can choose to use Counterspell as a Reaction. The Counterspell then comes in between the opponents Action, thus proving that Actions are divisible - not that we need that proof, since there is no general rule that they are not. Whether or not it succeeds at interrupting the spell is superfluous to what we are discussing.

You are correct in that there is no sentence that reads "Actions are atomic and cannot be divided except by special means." You really think that means the rules intend that ALL Actions are divisible infinitely? Is there such a thing as "starting to Dodge?" Can I Ready an Attack and if I see an enemy "Start to Dodge" I can attack them before their Dodge grants me Disadvantage? Seriously? That's a nifty way around Disengage too isn't it? I Ready my Attack and if my enemy "starts to Disengage" I'm going to attack them! Low Perception score? Just Ready an Attack Action for when your Rogue opponent "starts to Hide" and you needn't worry! If you're saying the Cast a Spell Action can be sub-divided because it doesn't use the words "Actions cannot be divided except by special means" then it applies equally to all of the Actions. How would you rule on a Wizard who says they will Ready Cast a Spell...to cast a spell on the fighter when they "Start to Ready an Action to Attack the wizard?" Who can interrupt who? The wizard wanted to cast the spell before the fighter was fully Readied, right? This is, apparently, the sort of shenanigans the rules intended?

"But none of those make sense, because you'd be better off just using your Action anyway!!" Exactly. Almost as if there was one particular case where this might be relevant (casting a spell), and the game designers built in a few ways to get around it...

I can certainly point to places in the PHB where it implies an Action is a discrete "thing" and/or details how the Attack Action specifically can be sub-divided when multiple attacks are involved.

Your Turn
On your turn, you can move a distance up to your speed and take one action. (not start to take, take, and finish taking, or declare, then start, then resolve if nothing interrupts)

Moving Between Attacks
If you take an action that includes more than one weapon attack, you can break up your movement even further by moving between those attacks.

Making an Attack
Whether you're striking with a melee weapon, firing a weapon at range, or making an attack roll as part of a spell, an attack has a simple structure.
(then goes on to list steps 1, 2, & 3.)

I'm not stating all Actions are inherently atomic. But those that the rules wanted sub-divided, the rules explicitly describe how they are sub-divided. The Attack Action has rules governing how it can be normally be split up. The rest can be interrupted by specific spells and/or abilities on a case-by-case basis, in accordance with specific beats general. An Action is a thing that you can do on your turn. The RAW states that when you take an Action, you get to take it. Certain abilities and spells may specifically pre-empt or interrupt that. It is super-rules lawyer to say that just because it doesn't say an Action is specifically un-interruptable that automatically means the rules intended for all Actions be be divisible and interruptible by basically anything.

On a side note, you agree and disagree with me in the same post! Your agree that the specific example of Counterspell interrupting an Action of Cast a Spell doesn't provide evidence that anything can interrupt Cast a Spell, then in the next sentence you state that Counterpsell is proof that Actions can be divided...

It is all getting rather circular at this point, personally I would be very interested to hear what the game designers intended in this matter.

[Mikal]

So regardless of all this talk about timing (seriously, my eyes glazed over after like the 7th page of it), one thing seemingly being ignored is that no matter when a caster is attacked, nothing says that you can actually disrupt their spell casting by damaging them. You can only force concentration checks on existing spell effects or spells that require more than 1 action to cast.

So sure. Let's say that you can somehow ready an action to "attack as soon as they start casting the spell". You do so, you hit them. That takes like less than a second. The caster then looks at you, and completes casting the spell, because what you did has zero effect whatsoever on their ability to cast a spell. Just like how grappling a character does not actually stop a caster from being able to cast the spell.

So... yeah. Go back to your pedantry about timing, but it literally RAW doesn't matter, since whichever way you rule, you ain't disrupting crap and at worst wasted your turn.