Can a player take the Ready Action and keep the same Trigger but change what was initially defined as their action?
Example:
When declaring the Ready Action, the Wizard wants to cast a fireball on a boat when given a specific range. While waiting for the trigger, a horde of goblins appears, and now the Wizard wants to change his Ready Action action.
I said the Trigger could not change since it starts your Action, but to keep things moving, I allowed the Wizard to fireball the goblins, not the boat.
Sometimes you want to get the jump on a foe or wait for a particular circumstance before you act. To do so, you can take the Ready action on your turn, which lets you act using your reaction before the start of your next turn.
First, you decide what perceivable circumstance will trigger your reaction. Then, you choose the action you will take in response to that trigger, or you choose to move up to your speed in response to it. Examples include "If the cultist steps on the trapdoor, I’ll pull the lever that opens it," and "If the goblin steps next to me, I move away."
When the trigger occurs, you can either take your reaction right after the trigger finishes or ignore the trigger.
When you ready a spell, you cast it as normal but hold its energy, which you release with your reaction when the trigger occurs. To be readied, a spell must have a casting time of 1 action, and holding onto the spell’s magic requires concentration (explained in chapter 10). If your concentration is broken, the spell dissipates without taking effect. For example, if you are concentrating on the web spell and ready magic missile, your web spell ends, and if you take damage before you release magic missile with your reaction, your concentration might be broken.
I would say that you can't change what you defined that you would do. But I'm not sure you need to be so specific when defining what you will do. Choosing your action might not require you to specify the target (if any).
Hmm, seems like what you are describing is actually different trigger, same action rather than the other way around like the thread title. And I generally put more emphasis on the player describing the trigger for an action than what the action itself does.
Hmm, seems like what you are describing is actually different trigger, same action rather than the other way around like the thread title. And I generally put more emphasis on the player describing the trigger for an action than what the action itself does.
The trigger was when the boat was at a specific range, sixty feet; then the Wizard would cast Fireball. While waiting for the ship to come within range, the horde of goblins showed up. Now the Wizard wants to change the target of the Fireball once the boat reaches sixty feet. Again, I was not letting him change his trigger for his action, even if it made no sense what the player was waiting for, given the action he wished to adjust to.
So I should be more open, allowing the action to be whatever the player wants to do once the trigger is met.
I'd agree with Thezzaruz that you can't change it. There's a risk inherent in readying an action, even more risks for a caster. Sometimes, things don't break your way.
If you take the alternative to its logical conclusion, then you could end up with a player saying, I'm going to ready my action for when x happens, but I don't actually know what I'm going to do yet. It just seems like it could open up lots of shenanigans. Especially in this edition, where things like delaying your turn (which is practically what they're doing) aren't a thing.
In this case, it seems like a small change -- its not like they wanted a different spell, just a different target -- but it still seems pretty abusable. Like the archer saying, I'm going to shoot at an enemy when it gets to a certain square, but when an enemy gets to that square, the archer's player decides it will be too hard to hit that one, so they shoot at a different enemy with a lower AC.
I'm not trying to be a stickler about this, and I'd probably let them do it. When a player at my table readies a spell, They just need to tell me they are readying a spell. I don't even need to know the trigger because I don't want it to influence the way I play enemy creatures in combat. This requires a fair bit of trust on my part that they are going to be straight with me about what their trigger actually was. But the way the rule is written, it seems like you pick your trigger, and you pick what it triggers, and then that shouldn't change after the fact. But if nobody other than the caster knows anyway, then I guess, what's the harm? :)
Sometimes you want to get the jump on a foe or wait for a particular circumstance before you act. To do so, you can take the Ready action on your turn, which lets you act using your reaction before the start of your next turn.
First, you decide what perceivable circumstance will trigger your reaction. Then, you choose the action you will take in response to that trigger, or you choose to move up to your speed in response to it. Examples include "If the cultist steps on the trapdoor, I’ll pull the lever that opens it," and "If the goblin steps next to me, I move away."
When the trigger occurs, you can either take your reaction right after the trigger finishes or ignore the trigger.
When you ready a spell, you cast it as normal but hold its energy, which you release with your reaction when the trigger occurs. To be readied, a spell must have a casting time of 1 action, and holding onto the spell’s magic requires concentration (explained in chapter 10). If your concentration is broken, the spell dissipates without taking effect. For example, if you are concentrating on the web spell and ready magic missile, your web spell ends, and if you take damage before you release magic missile with your reaction, your concentration might be broken.
I would say that you can't change what you defined that you would do. But I'm not sure you need to be so specific when defining what you will do. Choosing your action might not require you to specify the target (if any).
Yep, the special note is that you can ignore one trigger for the reaction and take the reaction if there's another trigger for it.
With this knowledge, the trick is to keep the triggers as broad and open as possible so you have more choice on when and how to execute the reaction. BUT if you allow it to be too broad then its ripe for a fair bit of unrealistic shenanigans.
A wizard might say "When someone moves within 60 feet of me, I cast a 3rd level spell". This is VERY open because they have only noted the spell slot being expended and that the trigger occurs when someone moves within 60 feet, that creature could already be within 60 feet and move inside that zone, they could also arrive at 60 feet but move a further 20 feet in before triggering the spell since they're moving WITHIN 60 feet of the wizard. SOMEONE could be friendly, enemy or neutral as well, allowing the wizard to wait until a number of enemies have moved then triggering it the moment an ally begins to move so the opponents have all had the chance to approach and bunch up. Noting that they're casting a 3rd level spell allows a lot of flexibility on them choosing any spells from 1st to 3rd level depending on what they've seen occur, it fits with the idea that enemies shouldn't know what you're casting RAW but probably goes too far technically since you cast the actual spell and hold it's energy. But even after all that, nothing is specified about what is done with the spell, if it's cast on self, ally, enemy or somewhere random.
If I'm understanding things correctly, the wizard set the trigger to be the boat coming within 60 feet but didn't specify the ship as the target, only that they cast Fireball. So a horde of goblins they didn't know about suddenly appears in range and when the boat comes within 60 feet, it gives the wizard the trigger but instead of casting fireball at the ship, they cast it at the goblins. Well... RAW, if the wizard didn't specify the target as being the ship then there's nothing stopping them from using the ship approach as the trigger but targeting the goblins instead.
This is really where the DM needs to come in with their decisions and arbitrations because the open statement example I gave is ripe for abuse. The DM needs to check the statement the player makes for their reaction and decide just how open ended they'll allow the statement to be. IMHO this can vary situation to situation. I suspect you probably made the right call in this instance, if the player didn't specify the ship as the target then an approaching goblin horde is pretty hard to miss once it's in 60 feet and I don't think it breaks reality to hard to say a wizard intending to target a ship, suddenly turns towards the, now obvious, goblin horde and unleashes their spell at it. I think its also reasonable for DMs to force certain ability checks on the players if you feel they're going too far from what their intended reaction was supposed to achive. For instance, you might have required a WIS Perception check on the goblins to see and adjust the reaction in time.
Readying an Action is a tradeoff. You get to do something on someone else's turn, but the tradeoff is that the triger might not happen and your action is wasted. Or, if you are a warrior, the tradeoff is that you can't use features like Extra Attack. Tradeoffs are great, as they provide meaningful choices.
Readying an attack or spellcasting doesn't require targeting in advance. so when readying a spell, it's cast and the energy held so you can't change the spell cast as a reaction but you can decide to place the spell where you want when releasing it as a reaction. Your target must be within range when you take a readied action, not when you first ready it.
Readying an attack or spellcasting doesn't require targeting in advance. so when readying a spell, it's cast and the energy held so you can't change the spell cast as a reaction but you can decide to place the spell where you want when releasing it as a reaction. Your target must be within range when you take a readied action, not when you first ready it.
But you still need to define the trigger to cast the spell as the reaction.
Readying an attack or spellcasting doesn't require targeting in advance. so when readying a spell, it's cast and the energy held so you can't change the spell cast as a reaction but you can decide to place the spell where you want when releasing it as a reaction. Your target must be within range when you take a readied action, not when you first ready it.
But you still need to define the trigger to cast the spell as the reaction.
Sure, but that action can be "I throw my fireball spell"
Not the lack of a specific target with that action statement. You have readied the fireball spell by casting it in your turn and are holding on to the energy with an intent to throw the fireball spell after the trigger is set.
So back to your original statement. Lets presume the exact wording of your player's reaction was this: "I ready an action to throw a fireball spell when the ship comes within 60 feet of me"
Nothing in that statement specifies the ship as the target. The primary restriction is that the ship must come within 60 feet. The goblin horde you mention, is not the ship, so they cannot trigger the action of "throw a fireball spell". If the ship stays where it is for the turn, the wizard will not have the opportunity to cast the fireball spell at all, BUT if the ship does come within 60 feet then they can "throw a fireball spell". Since no target is specified, they could throw it at the approaching ship, at the horde of goblins at an empty space within 60 feet somewhere or even at their own feet if they're feeling crazy.
BUT, if the statement is this: "I ready an action to throw a firball spell AT THE SHIP when the ship comes within 60 feet of me"
This more specific action also specifies the target and thus, would prevent the player changing target to anything other than the ship, unless the DM allowed them to.
Readying an attack or spellcasting doesn't require targeting in advance. so when readying a spell, it's cast and the energy held so you can't change the spell cast as a reaction but you can decide to place the spell where you want when releasing it as a reaction. Your target must be within range when you take a readied action, not when you first ready it.
But you still need to define the trigger to cast the spell as the reaction.
Yes it will depend of the trigger. ''I cast fireball when enemy comes within range'' is true when the boat's occupants come into range, so is when the goblin do. You can select to take your readied action whenever your trigger occur, you don't have to do so the first time it does necessarily.
Readying an attack or spellcasting doesn't require targeting in advance. so when readying a spell, it's cast and the energy held so you can't change the spell cast as a reaction but you can decide to place the spell where you want when releasing it as a reaction. Your target must be within range when you take a readied action, not when you first ready it.
But you still need to define the trigger to cast the spell as the reaction.
Sure, but that action can be "I throw my fireball spell"
In which case the trigger will never occur, because you won't throw your fireball spell until you notice yourself throwing a fireball spell.
RAW you declare an action and the trigger but it doesn'r specify how specific those are:
"I ready my action to cast a spell " , "I ready my action to cast fireball" and "I ready my action to cast a spell on at the ship" are all valid though a DM might decide one or more are not specific enough. If you say you ready a spell and as it approaches you see there are a load of hostages on board you can use your action to cast feeblemoind on the captain but if the action you described was to cast fireball you can not.
Here the wizard readied an action to cast fireball on the boat therefore his only option when the trigger occurs is to cast fireball on the ship or not do lose (and lose the spell slot), if he had instead just said he would ready the action to cast fireball then he could change the target.
It would however be a bit of a jerk of DM to penalise the player for not expecting the unexpected so if the DM would allow to ready an action to cast fireball without specifying the target they sohuld allow them to change the target even if they happen to mention the target with the readied action.
As a DM I require players to specify the spell when they ready the cast a spell action not not the target (a very common readied action is I cast firebolt if I see a hostile creature within its range)
Readying an attack or spellcasting doesn't require targeting in advance. so when readying a spell, it's cast and the energy held so you can't change the spell cast as a reaction but you can decide to place the spell where you want when releasing it as a reaction. Your target must be within range when you take a readied action, not when you first ready it.
But you still need to define the trigger to cast the spell as the reaction.
Sure, but that action can be "I throw my fireball spell"
In which case the trigger will never occur, because you won't throw your fireball spell until you notice yourself throwing a fireball spell.
I think you're misreading. BKThompson noted that you still need to define the TRIGGER to cast the spell as a reaction. My comment agreed with it ("sure") but noted that the ACTION associated with that could be "I throw my fireball".
Thats all in response to Plaguescarred's note that you don't need to specify a TARGET.
So in the case we're discussing TRIGGER: Ship comes within 60 feet of caster ACTION: Throw fireball
No mention of TARGET so when ship comes within 60 feet of caster and satisfies the TRIGGER, the ACTION of "Throw fireball" can be used at any target within range of the Fireball spell. The TARGET doesn't need to be the ship.
On the other hand, if I specified the ACTION as "Throw fireball at ship" then I wouldn't be able to throw the fireball at something else.
As I think most folks have said, you define a trigger and the action the character will take when the trigger happens. You then have the choice of taking the action or not when the trigger occurs. If you use the readied action, the character's reaction is used.
When casting a spell as a readied action, the spell is cast and the spell slot is expended. If the trigger does not occur before the character's next turn then the spell is lost.
In your example:
"When declaring the Ready Action, the Wizard wants to cast a fireball on a boat when given a specific range. While waiting for the trigger, a horde of goblins appears, and now the Wizard wants to change his Ready Action action."
The trigger in this case is when a boat reaches a specific range then they will release their fireball on the boat. The wizard casts the fireball and waits for the boat to come in range. If the boat doesn't come in range, the spell is lost. If something else happens like a better target appearing the wizard can't choose to cast their spell at it since it is not covered by the trigger they chose for casting the spell.
The wizard could choose any perceivable circumstance to trigger the spell but it has to be a specific circumstance. The wizard can't say "I'll cast the fireball when a good target shows up" since that isn't an perceivable circumstance - defining what is a "good" target isn't something that is perceivable because it is subjective.
The wizard could say they will cast the spell on the first enemy they see. However, this means that they might end up using the spell on one target. Or the wizard could say they will cast the spell when there are 3 creatures close enough together to be affected without hitting their allies. If that situation doesn't happen - e.g. three creatures run up and attack but there is no way to get them without fireballing allies then the spell will be lost.
In your example, RAW, the wizard can't change their trigger condition to be the group of goblins since the wizard has decided to wait for the boat to move closer to cast the spell.
In the end though, it is up to you how to run your game and also up to you how specific or general you allow your players to make the triggers for any Readied Actions they may have. It is up to the DM to judge what would be considered a "perceivable circumstance".
RAW you declare an action and the trigger but it doesn'r specify how specific those are:
"I ready my action to cast a spell " , "I ready my action to cast fireball" and "I ready my action to cast a spell on at the ship" are all valid though a DM might decide one or more are not specific enough. If you say you ready a spell and as it approaches you see there are a load of hostages on board you can use your action to cast feeblemoind on the captain but if the action you described was to cast fireball you can not.
Here the wizard readied an action to cast fireball on the boat therefore his only option when the trigger occurs is to cast fireball on the ship or not do lose (and lose the spell slot), if he had instead just said he would ready the action to cast fireball then he could change the target.
It would however be a bit of a jerk of DM to penalise the player for not expecting the unexpected so if the DM would allow to ready an action to cast fireball without specifying the target they sohuld allow them to change the target even if they happen to mention the target with the readied action.
As a DM I require players to specify the spell when they ready the cast a spell action not not the target (a very common readied action is I cast firebolt if I see a hostile creature within its range)
Just a quick comment
"I ready my action to cast a spell " , "I ready my action to cast fireball" and "I ready my action to cast a spell on at the ship" are all valid
None of these are actually valid readied actions.
When you ready a spell, the spell is cast and the spell slot expended on the caster's turn. This means that it has to be a specific spell that is readied. In addition, none of these specify a "perceivable circumstance" that could be used to trigger the spell.
"I ready my action to cast a spell at the ship" - this needs to specify what spell. In addition, if the trigger is the ship then what is it about the ship that would trigger the casting of the spell? Seeing the ship? Seeing the ship within range of the fireball?
"First, you decide what perceivable circumstance will trigger your reaction."
Basically, the trigger specified must be a perceivable circumstance - something concrete that can be perceived and doesn't require interpretation. "4 goblins in range of the spell" is a perceivable circumstance while "a good target" isn't since it is subjective.
RAW you declare an action and the trigger but it doesn'r specify how specific those are:
"I ready my action to cast a spell " , "I ready my action to cast fireball" and "I ready my action to cast a spell on at the ship" are all valid though a DM might decide one or more are not specific enough.
As DM i would require more elaborate trigger, to me it should include conditional circumstance along with "if" or "when" to be valid trigger. As the rule say, first, you decide what perceivable circumstance will trigger your reaction. Then, you choose the action you will take in response to that trigger, or you choose to move up to your speed in response to it.
So you're readying yourself for something to react to.
Sorry if I caused confusion for clarity I will define.
A "ready action" is the action you take on your turn, "First, you decide what perceivable circumstance will trigger your reaction. Then, you choose the action you will take in response to that trigger,"
A "triggered action" is the action you can choose to take when the trigger occurs in response to the trigger
My example of "I cast a fireball on the ship" was an example of a triggered action and is a valid triggered action. The readied action would also require a trigger such as "when the ship gets within range.
David is correct that while it doesn't say explicity, the fact that it uses the spell slot when you ready the spell implies that you decide to know the level of the spell and "holding onto its energy" probably means you need to specify what spell it is. The question is do you need ot specify the target as well.
If you do need to specify the target things get VERY iffy making readied actions very circumstancial. Say the centre of theship is 180 ft north of you and heading South you specify when the centre of the ship is 150 ft away I cast fireball centred on a point 150 ft north of me. If the ship vears to the side then your firball is likely to miss. The target of the fireball is a point in range so specifying the fireball is centred on the where the centre of the ship will be when the trigger occurs is not valid as that is an unknown location. If you can cast fireball on the centre of the ship whereever that happens to be (the "point you choose within range" is absolute not relative to a ship, a creature or anything else) when the trigger is met you can also cast the fireball oin the middle of the hoarde of goblins.
If you have to specify a target a readied action of "Ready a firebolt spell which I will release if I can see a hostile creature within its range" is not valid because it doesn't specify the target. This os probaly my most comon use of a readied action and I have never had a problem with it (with a lot of sifferent DMs)
Rollback Post to RevisionRollBack
To post a comment, please login or register a new account.
Can a player take the Ready Action and keep the same Trigger but change what was initially defined as their action?
Example:
When declaring the Ready Action, the Wizard wants to cast a fireball on a boat when given a specific range. While waiting for the trigger, a horde of goblins appears, and now the Wizard wants to change his Ready Action action.
I said the Trigger could not change since it starts your Action, but to keep things moving, I allowed the Wizard to fireball the goblins, not the boat.
Is that a legal move?
Ready action:
I would say that you can't change what you defined that you would do. But I'm not sure you need to be so specific when defining what you will do. Choosing your action might not require you to specify the target (if any).
Hmm, seems like what you are describing is actually different trigger, same action rather than the other way around like the thread title. And I generally put more emphasis on the player describing the trigger for an action than what the action itself does.
"Not all those who wander are lost"
The trigger was when the boat was at a specific range, sixty feet; then the Wizard would cast Fireball. While waiting for the ship to come within range, the horde of goblins showed up. Now the Wizard wants to change the target of the Fireball once the boat reaches sixty feet. Again, I was not letting him change his trigger for his action, even if it made no sense what the player was waiting for, given the action he wished to adjust to.
So I should be more open, allowing the action to be whatever the player wants to do once the trigger is met.
I'd agree with Thezzaruz that you can't change it. There's a risk inherent in readying an action, even more risks for a caster. Sometimes, things don't break your way.
If you take the alternative to its logical conclusion, then you could end up with a player saying, I'm going to ready my action for when x happens, but I don't actually know what I'm going to do yet. It just seems like it could open up lots of shenanigans. Especially in this edition, where things like delaying your turn (which is practically what they're doing) aren't a thing.
In this case, it seems like a small change -- its not like they wanted a different spell, just a different target -- but it still seems pretty abusable. Like the archer saying, I'm going to shoot at an enemy when it gets to a certain square, but when an enemy gets to that square, the archer's player decides it will be too hard to hit that one, so they shoot at a different enemy with a lower AC.
I'm not trying to be a stickler about this, and I'd probably let them do it. When a player at my table readies a spell, They just need to tell me they are readying a spell. I don't even need to know the trigger because I don't want it to influence the way I play enemy creatures in combat. This requires a fair bit of trust on my part that they are going to be straight with me about what their trigger actually was. But the way the rule is written, it seems like you pick your trigger, and you pick what it triggers, and then that shouldn't change after the fact. But if nobody other than the caster knows anyway, then I guess, what's the harm? :)
"Not all those who wander are lost"
Yep, the special note is that you can ignore one trigger for the reaction and take the reaction if there's another trigger for it.
With this knowledge, the trick is to keep the triggers as broad and open as possible so you have more choice on when and how to execute the reaction. BUT if you allow it to be too broad then its ripe for a fair bit of unrealistic shenanigans.
A wizard might say "When someone moves within 60 feet of me, I cast a 3rd level spell". This is VERY open because they have only noted the spell slot being expended and that the trigger occurs when someone moves within 60 feet, that creature could already be within 60 feet and move inside that zone, they could also arrive at 60 feet but move a further 20 feet in before triggering the spell since they're moving WITHIN 60 feet of the wizard. SOMEONE could be friendly, enemy or neutral as well, allowing the wizard to wait until a number of enemies have moved then triggering it the moment an ally begins to move so the opponents have all had the chance to approach and bunch up. Noting that they're casting a 3rd level spell allows a lot of flexibility on them choosing any spells from 1st to 3rd level depending on what they've seen occur, it fits with the idea that enemies shouldn't know what you're casting RAW but probably goes too far technically since you cast the actual spell and hold it's energy. But even after all that, nothing is specified about what is done with the spell, if it's cast on self, ally, enemy or somewhere random.
If I'm understanding things correctly, the wizard set the trigger to be the boat coming within 60 feet but didn't specify the ship as the target, only that they cast Fireball. So a horde of goblins they didn't know about suddenly appears in range and when the boat comes within 60 feet, it gives the wizard the trigger but instead of casting fireball at the ship, they cast it at the goblins. Well... RAW, if the wizard didn't specify the target as being the ship then there's nothing stopping them from using the ship approach as the trigger but targeting the goblins instead.
This is really where the DM needs to come in with their decisions and arbitrations because the open statement example I gave is ripe for abuse. The DM needs to check the statement the player makes for their reaction and decide just how open ended they'll allow the statement to be. IMHO this can vary situation to situation. I suspect you probably made the right call in this instance, if the player didn't specify the ship as the target then an approaching goblin horde is pretty hard to miss once it's in 60 feet and I don't think it breaks reality to hard to say a wizard intending to target a ship, suddenly turns towards the, now obvious, goblin horde and unleashes their spell at it. I think its also reasonable for DMs to force certain ability checks on the players if you feel they're going too far from what their intended reaction was supposed to achive. For instance, you might have required a WIS Perception check on the goblins to see and adjust the reaction in time.
Readying an Action is a tradeoff. You get to do something on someone else's turn, but the tradeoff is that the triger might not happen and your action is wasted. Or, if you are a warrior, the tradeoff is that you can't use features like Extra Attack. Tradeoffs are great, as they provide meaningful choices.
Readying an attack or spellcasting doesn't require targeting in advance. so when readying a spell, it's cast and the energy held so you can't change the spell cast as a reaction but you can decide to place the spell where you want when releasing it as a reaction. Your target must be within range when you take a readied action, not when you first ready it.
But you still need to define the trigger to cast the spell as the reaction.
Sure, but that action can be "I throw my fireball spell"
Not the lack of a specific target with that action statement. You have readied the fireball spell by casting it in your turn and are holding on to the energy with an intent to throw the fireball spell after the trigger is set.
So back to your original statement. Lets presume the exact wording of your player's reaction was this:
"I ready an action to throw a fireball spell when the ship comes within 60 feet of me"
Nothing in that statement specifies the ship as the target. The primary restriction is that the ship must come within 60 feet. The goblin horde you mention, is not the ship, so they cannot trigger the action of "throw a fireball spell". If the ship stays where it is for the turn, the wizard will not have the opportunity to cast the fireball spell at all, BUT if the ship does come within 60 feet then they can "throw a fireball spell". Since no target is specified, they could throw it at the approaching ship, at the horde of goblins at an empty space within 60 feet somewhere or even at their own feet if they're feeling crazy.
BUT, if the statement is this:
"I ready an action to throw a firball spell AT THE SHIP when the ship comes within 60 feet of me"
This more specific action also specifies the target and thus, would prevent the player changing target to anything other than the ship, unless the DM allowed them to.
Yes it will depend of the trigger. ''I cast fireball when enemy comes within range'' is true when the boat's occupants come into range, so is when the goblin do. You can select to take your readied action whenever your trigger occur, you don't have to do so the first time it does necessarily.
You just need to plan for all of those possibilities when you ready the action :)
"Not all those who wander are lost"
In which case the trigger will never occur, because you won't throw your fireball spell until you notice yourself throwing a fireball spell.
RAW you declare an action and the trigger but it doesn'r specify how specific those are:
"I ready my action to cast a spell " , "I ready my action to cast fireball" and "I ready my action to cast a spell on at the ship" are all valid though a DM might decide one or more are not specific enough. If you say you ready a spell and as it approaches you see there are a load of hostages on board you can use your action to cast feeblemoind on the captain but if the action you described was to cast fireball you can not.
Here the wizard readied an action to cast fireball on the boat therefore his only option when the trigger occurs is to cast fireball on the ship or not do lose (and lose the spell slot), if he had instead just said he would ready the action to cast fireball then he could change the target.
It would however be a bit of a jerk of DM to penalise the player for not expecting the unexpected so if the DM would allow to ready an action to cast fireball without specifying the target they sohuld allow them to change the target even if they happen to mention the target with the readied action.
As a DM I require players to specify the spell when they ready the cast a spell action not not the target (a very common readied action is I cast firebolt if I see a hostile creature within its range)
I think you're misreading. BKThompson noted that you still need to define the TRIGGER to cast the spell as a reaction. My comment agreed with it ("sure") but noted that the ACTION associated with that could be "I throw my fireball".
Thats all in response to Plaguescarred's note that you don't need to specify a TARGET.
So in the case we're discussing
TRIGGER: Ship comes within 60 feet of caster
ACTION: Throw fireball
No mention of TARGET so when ship comes within 60 feet of caster and satisfies the TRIGGER, the ACTION of "Throw fireball" can be used at any target within range of the Fireball spell. The TARGET doesn't need to be the ship.
On the other hand, if I specified the ACTION as "Throw fireball at ship" then I wouldn't be able to throw the fireball at something else.
As I think most folks have said, you define a trigger and the action the character will take when the trigger happens. You then have the choice of taking the action or not when the trigger occurs. If you use the readied action, the character's reaction is used.
When casting a spell as a readied action, the spell is cast and the spell slot is expended. If the trigger does not occur before the character's next turn then the spell is lost.
In your example:
"When declaring the Ready Action, the Wizard wants to cast a fireball on a boat when given a specific range. While waiting for the trigger, a horde of goblins appears, and now the Wizard wants to change his Ready Action action."
The trigger in this case is when a boat reaches a specific range then they will release their fireball on the boat. The wizard casts the fireball and waits for the boat to come in range. If the boat doesn't come in range, the spell is lost. If something else happens like a better target appearing the wizard can't choose to cast their spell at it since it is not covered by the trigger they chose for casting the spell.
The wizard could choose any perceivable circumstance to trigger the spell but it has to be a specific circumstance. The wizard can't say "I'll cast the fireball when a good target shows up" since that isn't an perceivable circumstance - defining what is a "good" target isn't something that is perceivable because it is subjective.
The wizard could say they will cast the spell on the first enemy they see. However, this means that they might end up using the spell on one target. Or the wizard could say they will cast the spell when there are 3 creatures close enough together to be affected without hitting their allies. If that situation doesn't happen - e.g. three creatures run up and attack but there is no way to get them without fireballing allies then the spell will be lost.
In your example, RAW, the wizard can't change their trigger condition to be the group of goblins since the wizard has decided to wait for the boat to move closer to cast the spell.
In the end though, it is up to you how to run your game and also up to you how specific or general you allow your players to make the triggers for any Readied Actions they may have. It is up to the DM to judge what would be considered a "perceivable circumstance".
Just a quick comment
"I ready my action to cast a spell " , "I ready my action to cast fireball" and "I ready my action to cast a spell on at the ship" are all valid
None of these are actually valid readied actions.
When you ready a spell, the spell is cast and the spell slot expended on the caster's turn. This means that it has to be a specific spell that is readied. In addition, none of these specify a "perceivable circumstance" that could be used to trigger the spell.
"I ready my action to cast a spell at the ship" - this needs to specify what spell. In addition, if the trigger is the ship then what is it about the ship that would trigger the casting of the spell? Seeing the ship? Seeing the ship within range of the fireball?
"First, you decide what perceivable circumstance will trigger your reaction."
Basically, the trigger specified must be a perceivable circumstance - something concrete that can be perceived and doesn't require interpretation. "4 goblins in range of the spell" is a perceivable circumstance while "a good target" isn't since it is subjective.
As DM i would require more elaborate trigger, to me it should include conditional circumstance along with "if" or "when" to be valid trigger. As the rule say, first, you decide what perceivable circumstance will trigger your reaction. Then, you choose the action you will take in response to that trigger, or you choose to move up to your speed in response to it.
So you're readying yourself for something to react to.
Sorry if I caused confusion for clarity I will define.
A "ready action" is the action you take on your turn, "First, you decide what perceivable circumstance will trigger your reaction. Then, you choose the action you will take in response to that trigger,"
A "triggered action" is the action you can choose to take when the trigger occurs in response to the trigger
My example of "I cast a fireball on the ship" was an example of a triggered action and is a valid triggered action. The readied action would also require a trigger such as "when the ship gets within range.
David is correct that while it doesn't say explicity, the fact that it uses the spell slot when you ready the spell implies that you decide to know the level of the spell and "holding onto its energy" probably means you need to specify what spell it is. The question is do you need ot specify the target as well.
If you do need to specify the target things get VERY iffy making readied actions very circumstancial. Say the centre of theship is 180 ft north of you and heading South you specify when the centre of the ship is 150 ft away I cast fireball centred on a point 150 ft north of me. If the ship vears to the side then your firball is likely to miss. The target of the fireball is a point in range so specifying the fireball is centred on the where the centre of the ship will be when the trigger occurs is not valid as that is an unknown location. If you can cast fireball on the centre of the ship whereever that happens to be (the "point you choose within range" is absolute not relative to a ship, a creature or anything else) when the trigger is met you can also cast the fireball oin the middle of the hoarde of goblins.
If you have to specify a target a readied action of "Ready a firebolt spell which I will release if I can see a hostile creature within its range" is not valid because it doesn't specify the target. This os probaly my most comon use of a readied action and I have never had a problem with it (with a lot of sifferent DMs)