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Re: Declaring before initiative, what is the source of this?

Posted: Thu Apr 04, 2019 11:54 am
by Ska
Nagora wrote:Actually, screw that. I'm going to try asking simple direct questions.

@Ska: when a cleric casting a 6 segment spell is delayed by 5 segments, what is the procedure on the following round for determining the time her next spell is cast?
If the cleric is delayed from casting ( for some reason he cannot begin) for 5 segments then we need to know when he was supposed to have begun casting. Once know that add 5 segments and begin adding casting time.

So if cleric won with 6 and opponents rolled 1, the cleric normally starts casting on segment 1 but for some reason cannot until segment 6. Assuming the cleric survives attack on segment 6 and is not disrupted his spell will work on segment 1 of the next combat round.

Re: Declaring before initiative, what is the source of this?

Posted: Thu Apr 04, 2019 12:08 pm
by AxeMental
Nagora wrote:
AxeMental wrote:
Nagora wrote:Actually, screw that. I'm going to try asking simple direct questions.

@Ska: when a cleric casting a 6 segment spell is delayed by 5 segments, what is the procedure on the following round for determining the time her next spell is cast?
I can't answer for SKA but, if the enemy rolled a 5 on initiative, that means the spell caster (who was delayed until then) can start casting on segment 5. So, 5+6=11 segments (therefore it carries over into segment 1 of the next round). Other DMs might rule differently, but I wouldn't allow the caster to do anything else that round (cast another spell, attack etc.). Thats the risk of using a long spell.

If the spell was begun on segment 6 of the round, it would go off on the second segment of the following round. So, if the initiative rolls were PCs 1, monsters 5, the monsters would get their telling blows in on the first segment (and be able to disrupt the spell if they hit the caster). The caster would not be able to do another action that round.

That is how I would do it anyway.
OK. I have a question about that specific answer: you say that "if the enemy rolled a 5 on initiative, that means the spell caster (who was delayed until then) can start casting on segment 5. So, 5+6=11" but that seems wrong to me (I should have used a 7-segment spell but since we're here now...). If the spell was one segment long, would it not go off on segment 5? Therefore this spell would go off on segment 10? It seems that running it per your answer no spell, other than perhaps feather fall, would complete on segment 1. Is that right?
If you start a 1 segment spell on segment five it goes off at the end of segment 5 (at the end of that 1-6 second blip of time).

If you'd used a 9 segment spell and it is started on segment 5 (because thats what the enemy dice role indicates) it goes off on 5+9=14. There are only 10 segments in a round (each segment is 6 seconds long and all 10 equal 1 minute). So that means the spell carries over to segment 4 of the following round. That means for the first 4x6= 24 seconds of the next round the guy is still casting the spell from the previous round. That means if the PCs roll a 1, 2, 3 on their d6 for initiative (when the other side gets in their meaningful hit), its possible the monsters can hit the caster and break his spell. If the monsters see some guy casting a long ass spell, you can bet they sure as shit will try (like I said thats the risk of long ass spells).

It sucks and all I know. But...

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Re: Declaring before initiative, what is the source of this?

Posted: Thu Apr 04, 2019 1:36 pm
by T. Foster
For me, the key textual support for the "actions begin on initiative" interpretation is on PH p. 104, the section labeled "Spell Combat:"
PH p. 104 wrote:Spell Combat:
Unless combat is spell versus spell, many such attacks will happen near the end of a melee round. This is because the spell requires a relatively lengthy time to cast, generally longer as spell level increases, so high level spells may take over a full melee round to cast. Furthermore, if the spell caster is struck, grabbed, or magically attacked (and fails to make the requisite saving throw - explained later), the spell will be spoiled and fail. Spell combat includes cleric and magic-user, as well as monster-oriented spells. Curative spells are handled likewise.
Remember that this is the PH so it's not giving the actual mechanics, but rather a sort of narrative description of how things work in play. There are a couple of key points here:

"many such attacks will happen near the end of a melee round. This is because the spell requires a relatively lengthy time to cast" - I interpret "near the end of the melee round" as meaning something like segments 7-10. Most combat-oriented spells don't have casting times that long, 3 to 5 segments is more common, so if many spell attacks are occurring near the end of the round that timing must include some sort of delay.

"high level spells may take over a full melee round to cast" - there are spells that take more than a round to cast, that have casting times in rounds, or turns, or hours. However, these are not generally combat-oriented spells, nor are they particularly unique or even more prevalent at high levels (there are numerous 1st level cleric and magic-user spells with casting times of 1 full round or longer: Create Water, Detect Evil, Comprehend Languages, Find Familiar, Identify, etc.). But there are many combat-oriented high level spells that have casting times of 6-9 segments. With a delay built in, those spells very well may end up taking more than a full melee round to cast (but OTOH they also may not - with a lucky initiative roll even a 9-segment spell might go off in a single round, which is why the quote doesn't say "certain spells will take more than one round to cast").

If there is no initiative-based delay in casting, then neither of these clauses makes sense.

Yes, it's open to interpretation because it's being intentionally vague about the actual mechanics, and we know that the mechanics are not clearly or consistently explained in the DMG, but I feel that the "delayed action" interpretation produces results that much more closely resemble the narrative description here than the alternative.

As to why there's no clear, unambiguous reference to actions starting on the segment indicated by the initiative die (except on p. 65), we shouldn't completely discount the possibility that such text was left out by editorial error or oversight. We know something similar happened in other cases - for instance, we've determined that the Naval Combat rules in the DMG are missing most of the Naval Combat rules from OD&D vol. III and present only additions and clarifications without the underlying text, which makes them very confusing and seemingly woefully incomplete. There are other examples - how often wandering monster checks supposed to be made is only defined by inference (e.g. in the example of play). We also know that, since Gary Gygax didn't actually use the rulebooks, because he had all of this in his head, he tended not to notice these sorts of errors and omissions until long after the fact, if ever: the falling damage rule in the PH went uncorrected until 1982; in 1985 Gary in Dragon and Polyhedron was addressing errors and omissions in the MMII and WOG boxed set that had been published two years earlier; he claimed in his foreword to some 90s-era netbook not to have realized that halflings weren't given the same AC bonus against large humanoids as dwarfs and gnomes and that they should have; he didn't clarify the "positive energy plane" error in the MM mummy description until online Q&A in the 2000s; etc.

Literally for all we know there was supposed to be a paragraph in the DMG explaining that the initiative die determines the segment of the round on which actions occur (or commence), and Gary never realized it wasn't there, and that "note 2" on p. 65 was intended as a reminder of the general rule, not as a new rule. Even the mysterious "whichever is applicable" in the note could be explained if the hypothetical missing piece of corresponding text explained that initiative can either be roll-high with actions commencing on the segment indicated by the other side's die, or roll-low with action commencing on the segment of your own die.

This scenario is sure to be dismissed by those who are invested in the other interpretation, but it really is plausible - that a piece of text got lost between Gary's typescript and the layout, or was inadvertently cut for space/formatting issues, or was cut from one page and intended to be re-inserted somewhere else but wasn't. Things like this absolutely happened on multiple occasions with the AD&D rulebooks that we know of, and we can only speculate about how many times they happened that we don't.

Re: Declaring before initiative, what is the source of this?

Posted: Thu Apr 04, 2019 2:03 pm
by Nagora
AxeMental wrote:
Nagora wrote:OK. I have a question about that specific answer: you say that "if the enemy rolled a 5 on initiative, that means the spell caster (who was delayed until then) can start casting on segment 5. So, 5+6=11" but that seems wrong to me (I should have used a 7-segment spell but since we're here now...). If the spell was one segment long, would it not go off on segment 5? Therefore this spell would go off on segment 10? It seems that running it per your answer no spell, other than perhaps feather fall, would complete on segment 1. Is that right?
If you start a 1 segment spell on segment five it goes off at the end of segment 5 (at the end of that 1-6 second blip of time).
So, if there was some continuing action from the previous round (such as movement) which required 6 segments to complete, the 1 segment spell would, if the caster's foe rolled a 5 for initiative, complete first. Is that right? I'm trying to understand what happens in this system if a caster is casting a 1-segment spell and a bowman attacks and they both roll a 1 for initiative. Is it fair to say that you see both actions as completing/happening on segment-1?
Ska wrote:If the cleric is delayed from casting ( for some reason he cannot begin) for 5 segments then we need to know when he was supposed to have begun casting. Once know that add 5 segments and begin adding casting time.

So if cleric won with 6 and opponents rolled 1, the cleric normally starts casting on segment 1 but for some reason cannot until segment 6. Assuming the cleric survives attack on segment 6 and is not disrupted his spell will work on segment 1 of the next combat round.
OK. And do you agree that there is no text stating, or example of, that in the book? Nice simple question.
AxeMental wrote:
Nagora wrote:
p65DMG wrote:Attacks directed at spell casters will come on that segment of the round shown on the opponent’s or on their own side’s initiative die, whichever is applicable. (If the spell caster’s side won the initiative with a roll of 5, the attack must come then, not on the opponent’s losing roll of 4 or less.) Thus, all such attacks will occur on the 1st-6th segments of the round.
Say the caster's side (casting magic missile) rolls a 4 and the enemy war dog rolls a 3. Caster wins. What segment does the war dog get its bite? Whichever segment you feel is right there's no problem here so far.

Now say the caster's side rolls a 3 and the war dog rolls a 4. The war dog won, yet the book says its attack will come on the segment of the "applicable" die roll. Neither the 3rd nor the 4th segment happens before a magic missile can be cast. This puts the book at odds with the spell always starting at the beginning of the round.
Take a look at the bolded area above.

I think you need to come to grips with this rule ("Attacks directed at spell casters will come on that segment of the round shown on the opponent’s or on their own side’s initiative die whichever is applicable").

At this point you seem to be ignoring it.
I'm currently ignoring the "or" as an advanced topic. I carefully addressed the rest of it in my answer to you on page 9 of the thread, which you seem to be ignoring yourself. Is it the "or" you're referring to? If so, how do you read that? If not, leave it for now and we can come back to it and you can just respond to my argument in my previous response to you asking about this section of the rules.
T. Foster wrote:For me, the key textual support for the "actions begin on initiative" interpretation is on PH p. 104, the section labeled "Spell Combat:"
I'm going to clip most of your post Trent (edit: I didn't in the end) as the others are covering most of the ground but I would point out that the DMG is known not to deliver all the aspects of combat mentioned in PHB. There is no special system for duels, for example. But even so...
PH p. 104 wrote:Spell Combat:
Unless combat is spell versus spell, many such attacks will happen near the end of a melee round.
Not "may roll over to the next round".
This is because the spell requires a relatively lengthy time to cast, generally longer as spell level increases, so high level spells may take over a full melee round to cast.
Again, a simple statement that some spells take more than a round. Which brings up the question of why there's no 12 segment spells. There's 9-segment spells, and there's 1-round spells, and even 1-turn and longer spells. But no 12-segment spells - not in PHB, not in UA, not in any module. Almost, almost, as if the designer was carefully avoiding the issue of having spells complete part way through the next round. Almost, in fact, as if the melee round was supposed to be a self-contained unit.
"many such attacks will happen near the end of a melee round. This is because the spell requires a relatively lengthy time to cast" - I interpret "near the end of the melee round" as meaning something like segments 7-10. Most combat-oriented spells don't have casting times that long, 3 to 5 segments is more common, so if many spell attacks are occurring near the end of the round that timing must include some sort of delay.
There's a fair number of clerical spells with 7-segment casting times that might get cast in combat. Neutralize Poison, Cause Serious Wounds, for example. Flame Strike is 8-segments.
"high level spells may take over a full melee round to cast" - there are spells that take more than a round to cast, that have casting times in rounds, or turns, or hours. However, these are not generally combat-oriented spells, nor are they particularly unique or even more prevalent at high levels (there are numerous 1st level cleric and magic-user spells with casting times of 1 full round or longer: Create Water, Detect Evil, Comprehend Languages, Find Familiar, Identify, etc.). But there are many combat-oriented high level spells that have casting times of 6-9 segments. With a delay built in, those spells very well may end up taking more than a full melee round to cast (but OTOH they also may not - with a lucky initiative roll even a 9-segment spell might go off in a single round, which is why the quote doesn't say "certain spells will take more than one round to cast").

If there is no initiative-based delay in casting, then neither of these clauses makes sense.
I find it hard to accept that statements which are clearly true make no sense. There are high level spells that take more than a round to cast; there are many of high level combat spells which take most of a round to cast. And they "take more than a round to cast" in a much more objective way than you present here - they actually have casting times of more than one round. Reading this as meaning that when you add an invisible die to the casting time the result is greater than 10 is wishful thinking, IMO. The text doesn't say "may take more than a round to cast".
Yes, it's open to interpretation because it's being intentionally vague about the actual mechanics, and we know that the mechanics are not clearly or consistently explained in the DMG,
I think it's remarkably consistent, actually. Certainly not clear, though.
As to why there's no clear, unambiguous reference to actions starting on the segment indicated by the initiative die (except on p. 65), we shouldn't completely discount the possibility that such text was left out by editorial error or oversight. We know this happened - for instance, we've determined that the Naval Combat rules in the DMG are missing most of the Naval Combat rules from OD&D vol. III and present only additions and clarifications without the underlying text, which makes them very confusing and seemingly woefully incomplete.
I agree and if I had to add reams and reams of text to make it work I would hardly bother debating it. But "Actions other than weapon combat commence at the start of the round" isn't a huge amount of text to add. If you're willing to add all the stuff needed to clarify d6+, and ignore where it contradict what is printed, then surely you can indulge me in one little bit. And we do know that something was left out - there's a cross-reference to Combat Procedure which goes no where.
Literally for all we know there was supposed to be a paragraph in the DMG explaining that the initiative die determines the segment of the round on which actions occur (or commence), and Gary never realized it wasn't there, and that "note 2" on p. 65 was intended as a reminder of the general rule, not as a new rule. Even the mysterious "whichever is applicable" could be explained if the hypothetical missing piece of corresponding text explained that initiative can either be roll-high with actions commencing on the segment indicated by the other side's die, or roll-low with action commencing on the segment of your own die. This scenario is sure to be dismissed by those who are invested in the other interpretation, but it really is plausible.
Its the stacking up of "well, that might be missing" bits that's the issue, not the existence lacunae in themselves. To have to appeal to missing text once is unfortunate, to have to do it four or five times starts to seem like something else.

Anyway, all this text leaves a big door here for Ska to ignore my direct question but maybe he'll answer and we can make some progress.

Re: Surprise and spell casting (over the length of the surpr

Posted: Thu Apr 04, 2019 3:03 pm
by Philotomy Jurament
Nagora wrote:Assume the opposition has a bowman with 18DEX; how do you run it?
The archer's 18 Dex negates his two segments of surprise. Assuming the archer has a strung bow in hand and is not in melee striking range of any enemies, I'd allow him to begin acting at the same time as the MU. He'd get his first arrow shot at the start, and given the 3 segment casting time of fireball, I'd allow that shot to interrupt the MU's spell if it hits the MU. The archer would potentially get a second shot later in the round, but the exact details of that would depend on the situation. Assuming enough distance is between the groups (which seems likely, given the use of fireball), I'd expect something like the party charging and his second shot happening as they came into closer range. Basically, I'd rule on the second shot based on the circumstances and the actions of the combatants.

Re: Declaring before initiative, what is the source of this?

Posted: Thu Apr 04, 2019 4:18 pm
by AxeMental
Negora wrote: So, if there was some continuing action from the previous round (such as movement) which required 6 segments to complete, the 1 segment spell would, if the caster's foe rolled a 5 for initiative, complete first...

I broke off my longer explanation into another thread, because I'm not certain how to handle it BtB.

As for this bit here (if I'm understanding the question) some action is carried over into the next round (in this case for 6 segments). Then if initiative is rolled and the DM roles 3 and the PCs role a 5, then yes the PCs go first, all except the guy who's completing his task which finishes on segment 6. That means the enemy can attack him on segment 5 (arrows swords and spells). If the enemy goblin shaman's casting time is 1 segment then it would go off at the end of segment 5 (or as some like to show it d6+1-1) and if cast at the person attempting to complete some task (like finish a spell of his own or summon or demon or what have you) and his spell works, he could disrupt the action.

Re: Declaring before initiative, what is the source of this?

Posted: Thu Apr 04, 2019 4:24 pm
by AxeMental
T. Foster wrote: Literally for all we know there was supposed to be a paragraph in the DMG explaining that the initiative die determines the segment of the round on which actions occur (or commence), and Gary never realized it wasn't there, and that "note 2" on p. 65 was intended as a reminder of the general rule, not as a new rule. Even the mysterious "whichever is applicable" in the note could be explained if the hypothetical missing piece of corresponding text explained that initiative can either be roll-high with actions commencing on the segment indicated by the other side's die, or roll-low with action commencing on the segment of your own die.

This scenario is sure to be dismissed by those who are invested in the other interpretation, but it really is plausible - that a piece of text got lost between Gary's typescript and the layout, or was inadvertently cut for space/formatting issues, or was cut from one page and intended to be re-inserted somewhere else but wasn't. Things like this absolutely happened on multiple occasions with the AD&D rulebooks that we know of, and we can only speculate about how many times they happened that we don't.
This makes alot of sense. As you and others have stated, EGG used low role goes first on a d10 (but he had to be aware there were those that preferred the larger number winning, I wonder if he used this method pre-1E). At that time the DMG was only for the DMs not the players (so he probably figured he was upgrading guys used to the older version, so they'd want high role goes first, but he must have thought they'd figure it out (and more then likely info was omitted as you suggested).

Re: Declaring before initiative, what is the source of this?

Posted: Thu Apr 04, 2019 8:22 pm
by Ska
Nagora, Foster provided the text from the PHB in his last post which answers the question you had. It states high level spells may take more than a full melee round to cast. Again you may not like these words but they are there. Clearly spells may take longer then one round to cast.

You keep asking for where in the rule books does it say A or B and when that is provided you again ask for where do the rules say A or B.

You have been provided where text shows initiative determines when spell casting begins and that spells can take longer then one round to cast.

Re: Declaring before initiative, what is the source of this?

Posted: Thu Apr 04, 2019 9:38 pm
by T. Foster
More grist for the mill - courtesy of EGG in Dragon #60 (April 1982):
The segment of the round in which the cantrip is cast is dependent on the usual factors: surprise, initiative, and so on. After the first of the two cantrips is cast, the magic-user must roll a four-sided die to determine how many segments later he or she will be able to cast the second cantrip
So per the author of the game speaking in an official capacity, initiative is one of the “usual factors” determining “the segment of the round” in which spells are cast. Some will doubtlessly dismiss this as a meaningless non-canonical secondary reference, or perhaps suggest that Gary Gygax didn’t understand or wasn’t qualified to speak on the rules of his own game, but for those who are interested in intent, this is a pretty clear reference, and much “closer to the ground” than 21st century email correspondence.

Re: Declaring before initiative, what is the source of this?

Posted: Thu Apr 04, 2019 11:12 pm
by EOTB
Clear to me, and also if I may point out, consistent with the Polyhedron reference to spell like powers which also came in '82 or '83. I'll quote my earlier post so that the two are seen in tandem.
EOTB wrote:Here's an interesting Q&A in Polyhedron regarding "Other actions don't start on a rolled segment."
Q: Do creatures with "spell-like powers"
need to cast the "powers" like spells?
Can you interrupt them, like with spellcasters,
and ruin the effects?

A: Spell-like powers are not spells, and
do not need to be "cast." They can be
produced in total silence, for example,
and in 1 segment of concentration. Thus,
they can only be interrupted if a blow
connects during that same segment -

and if the creature sees a swing coming,
it can easily delay a bit to avoid interruption.
Why would this answer be given if segments aren't tracked at all and nothing happens in a specific segment - only relative to each other in an abstract, changing order?

How is it even possible to give that answer conceptually if the other is true?
Although not directly applicable to the "citation" issue, I'd also point out that spell-like powers flip the "delay advantage" from the fighter attacking a spellcaster, to the creature with spell like powers being attacked by the fighter. There are no cues to the fighter when the power is being activate - no verbal, somatic, or material elements. A delaying fighter hoping to interrupt a spell like power can't be sure it will even be used that round, and so delay may accomplish nothing.

It makes spell like powers much more frightening than casting, as there's almost no hope of avoiding the creature's intent.

Re: Declaring before initiative, what is the source of this?

Posted: Fri Apr 05, 2019 12:35 am
by Ratbreath
Nagora wrote:I dealt with that in detail on the previous page. The dog attacks before the spell because it had initiative -bear in mind that in this situation the dog is standing right beside the MU. We can see (as explained previously) that this segment of the rules applies to casters who win initiative, just as the section on melee weapon speeds Vs spells does. If you can find a hole in that logic (please read the post on the previous page) then I'm happy to hear it, but I'm not going to type it out yet again.
No, you really didn't. When I first raised the issue on p5 of this thread you chose to utterly ignore it along with the other conflict your system has with the book which I asked you about. Rather rude, that. On p9 Axe asked you again and you typed up a lengthy, detailed post addressing everything except the actual thing you were asked about. Now you're saying that you're ignoring the part where your way conflicts with the books because it's an "advanced topic"? Weak.

Re: Declaring before initiative, what is the source of this?

Posted: Fri Apr 05, 2019 2:33 am
by Nagora
Ska wrote:Nagora, Foster provided the text from the PHB in his last post which answers the question you had. It states high level spells may take more than a full melee round to cast.
Yeah, I can read. The PHB is full of high level spells which take more than a full melee round to complete. Who ever said it didn't?
Again you may not like these words but they are there. Clearly spells may take longer then one round to cast.
You seem keen to fill your posts with anything except answers to direct questions.
You keep asking for where in the rule books does it say A or B and when that is provided you again ask for where do the rules say A or B.
I keep asking and you keep answering with text that says something else and saying that the meaning is "logically" what you had pre-determined it must be. That's why I'm asking you for specific text that tells the reader how to proceed with the d6+ system, which has several important, game-affecting aspects that players need to be aware of.
You have been provided where text shows initiative determines when spell casting begins and that spells can take longer then one round to cast.
Neither of those bits of text are in dispute. The dispute is your application of a particular interpretation of them to mean something that doesn't withstand any inspection and then trying to pull the "I'm playing BtB, you should go away" routine on alternative interpretations.

So I repeat my question: do you agree that there is no text that tells us how to handle initiative for a spell caster who's spell spills over into the next round?. I'm not saying that a lack of that text is a fatal flaw in itself, I just want to establish that you agree that it is missing.

Assuming that you manage to answer that with a simple "I agree" then my next question is: what happens if an attacker with a bow rolls 5 for initiative and the spellcaster rolls 2 while casting a 2-segment spell?

As an aside to the others, I'm aware that Gary had changed his position by the time he was working on UA, the cantrip rules seem to make that clear. Polyhedron's ruling is interesting but raises other issues and is from the same period. As far as I know the idea of treating spell-likes as having 1-segment casting times is completely new to that quote, isn't it?

Ratbreath: I'll come back to your question asap (I do remember it and I honestly thought I had answered it, but apparently not) but I want to focus on getting Ska to answer some simple questions unevasivly. As to Axe, I thought he was asking about the 1-6 part rather than the "or" part; he hasn't said otherwise since.

Re: Declaring before initiative, what is the source of this?

Posted: Fri Apr 05, 2019 3:02 am
by Nagora
EOTB wrote:Although not directly applicable to the "citation" issue, I'd also point out that spell-like powers flip the "delay advantage" from the fighter attacking a spellcaster, to the creature with spell like powers being attacked by the fighter. There are no cues to the fighter when the power is being activate - no verbal, somatic, or material elements. A delaying fighter hoping to interrupt a spell like power can't be sure it will even be used that round, and so delay may accomplish nothing.

It makes spell like powers much more frightening than casting, as there's almost no hope of avoiding the creature's intent.
I actually think the Polyhedron quote waters them down from the DMG. I've never seen any indication before that they could even be interrupted except by death (or have a casting time), and I've always played them that way no matter what initiative system I was using.

Re: Declaring before initiative, what is the source of this?

Posted: Fri Apr 05, 2019 7:06 am
by Ska
Nagora I have no doubt you can read but doubt your understanding of what you are reading.
Yes the rules do tell us what happens with a spell that carries over. The rule books denote a PC may take an action
during a combat round. Now let's combine that with the written words which tell us some spells will be completed in the next round. The answer: the casters action in the next round will be finishing the spell.

Your second question. Bowman rolls 5 magic user 2 and wants to cast 2 seg spell. On segment 2 bowman attacks caster. Caster hit and killed or not killed and begins casting in segment 5 and completes spell on segment 6.

Re: Declaring before initiative, what is the source of this?

Posted: Fri Apr 05, 2019 8:21 am
by Nagora
Ska wrote:Nagora I have no doubt you can read but doubt your understanding of what you are reading. Yes the rules do tell us what happens with a spell that carries over.
Great! What's the page number on that? I'm particularly interested in how that interacts with everyone else's initiative rolls. For example, how do we know if an attacker with a shortsword is able to attack the magic user before completion, and does the magic user get the use of DEX bonuses to AC for any part of the round? Where is that all explained? Because none of these things are even questions if spell-casting starts, like everything else, at the start of the round.
The rule books denote a PC may take an action during a combat round.
Now let's combine that with the written words which tell us some spells will be completed in the next round.
OK. I notice those words are not in my copy, though. Mine just notes the existence of high-level spells that take longer than a round to cast. There's no reference anywhere to spells "completing in" the next round, of course, as the designers made sure they avoided that exact issue, as I pointed out to Trent.
The answer: the casters action in the next round will be finishing the spell.
Okay. So, I'll put you down as agreeing that this is all constructed and not actually said in the text. You're inferring. Admittedly, you had to change some of the words but, still, there's nothing inherently wrong with inferring from clues.
Your second question. Bowman rolls 5 magic user 2 and wants to cast 2 seg spell. On segment 2 bowman attacks caster. Caster hit and killed or not killed and begins casting in segment 5 and completes spell on segment 6.
OK. So if the caster loses initiative he's better off losing it by a lot, right? In fact, generally speaking, this system makes spell casting a lot safer than I expected. If I'm casting a 2-segment spell, then the only way to prevent the casting is to kill me before it completes or strike on one of the two segments of casting. That is pretty generous and I wonder how wide-spread this ruling is even among d6+ DMs

Does the caster have their AC bonus in this case, then?

Is there any discussion anywhere in the books about the idea that a spellcaster can: a) Declare an intent to spellcast at the start of a round, b) Be struck for damage between that declaration and completion, and c) Still successfully cast the spell?

If you can relate that answer and your answer to the previous question about the bowman to:
DMG p65 wrote:Any successful attack, or non-saved-against attack upon the spell caster interrupts the spell.

Because spell casting will be so difficult, most magic-users and clerics will opt to use magical devices whenever possible in melee, if they are wise.
That would be good.