So Agonizing blast lets you do what its always done, only you have the option of having it apply to a different warlock spell rather than Eldritch blast as long as it's a "warlock cantrip" (it can be taken multiple times as well, tho I'm sure for technical reasons this is not reflected in platform) and Pact of the Tome lets you take a bunch of cantrips from whatever class and have them designated as "Warlock cantrip"
Is it thus reasonable to assume, that a player can take, say, "Shocking grasp" via Pact of the Tome, and apply Agonizing Blast to it? Or does this not work because of how that the cantrips gained from the Tome can be changed on a short rest? Such is to ask, does the invocation Agonizing Blast require warlock cantrips with permanence?
Agonizing Blast refers to "one of your known Warlock cantrips", while Pact of the Tome says you have those cantrips prepared. It's not 100% clear whether Agonizing Blast is using that term because they want to distinguish your permanent cantrips from the the rest, or if they're just sticking to convention (the rules rarely speak of cantrips as being prepared.)
One bit of circumstantial evidence in favor is that you could potentially swap out one of your "permanent" cantrips on level up and render Agonizing Blast temporarily unusable without ever messing with Pact of the Tome.
My gut feeling is that it's intended. The 2024 rules did away with the distinction between "known spells" and "prepared spells" for level 1+ spells in the various spellcasting classes; they're all just prepared spells now. Heck, Pact of the Tome has no issue saying that the spells you choose must be spells you don't have prepared already, which would include the cantrips too. I'm not sure why they've continued to use the "you learn/know" terminology for cantrips despite that, but I don't think it's meant to denote a distinct thing.
If I'm not mistaken, one way of getting good cantrips and using them as Warlock spells is through the Pact of the Tome. You could then choose, for example, Ray of Frost or Acid Splash and enhance them with Agonizing Blast.
I think this could have been fixed if the cantrip that Agonizing Blast is being used on could be changed on a long rest.
Technically all spells from Pact of the Tome are Warlock spells and so the cantrips would be Warlock Cantrip, thus I'd say it works but you can only benefit from this benefit while you have the cantrip available from Pact of the Tome and it is cast as a Warlock spell using Warlock's spell attack modifier (Charisma).
It appears spells you choose with Pact of the Tome are prepared cantrips you can cast despite not being known cantrip for your Warlock per se, making them ineligible with features affecting known cantrips specifically.
Gaining Spells: Before you can cast a spell, you must have the spell prepared in your mind or have access to the spell from a magic item, such as a Spell Scroll. Your features specify which spells you have access to, if any; whether you always have certain spells prepared; and whether you can change the list of spells you have prepared.
It appears spells you choose with Pact of the Tome are prepared cantrips you can cast despite not being known cantrip for your Warlock per se, making them ineligible with features affecting known cantrips specifically.
Gaining Spells: Before you can cast a spell, you must have the spell prepared in your mind or have access to the spell from a magic item, such as a Spell Scroll. Your features specify which spells you have access to, if any; whether you always have certain spells prepared; and whether you can change the list of spells you have prepared.
I decided to have a re-read and decided to focus on the word known. Known is not properly defined from what I can see, it's mentioned once in pact magic, that at level 1 you know 2 cantrips and then you learn more at levels 4 and 10.
The spells from pact of the tome are prepared but no mention of known.
Checking other classes, it would appear that levelled spells are prepared and cantrips are known, so this seems more likely to be an oversight in that it should say the cantrips from book of the tome are known, as cantrips are never prepared. This could be wrong of course, but looking at other features and feats that add cantrips like Magic Initiate and Blessed Warrior, these also say "learned" as opposed to "prepared".
RAW I'd have to agree with you , nothing says you "know" the cantrip from pact of the tome but I don't see any other cases of cantrips being "prepared", which is what pact of the tome implies, so I'd say RAI is that all cantrips must be known to be cast and thus count as known while holding the pact of the tome.
More so given this part of pact magic:
If another Warlock feature gives you spells that you always have prepared, those spells don’t count against the number of spells you can prepare with this feature, but those spells otherwise count as Warlock spells for you.
While it comes from an invocation, eldritch invocation itself is a Warlock Feature and similar text disappeared from Pact of the Tome from 2014 to 2024, likely because it's now already essentially covered in the Pact Magic feature itself.
Overall, it's another unclear and inconcise area of 2024.
I think this could have been fixed if the cantrip that Agonizing Blast is being used on could be changed on a long rest.
This would pretty much make the Repeatable portion of the invocation irrelevant, but I'm not sure how often people will actually take it more than once anyway. (Maybe a character with one melee cantrip and one ranged cantrip that both see frequent usage)
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Active characters:
Carric Aquissar, elven wannabe artist in his deconstructionist period (Archfey warlock) Lan Kidogo, mapach archaeologist and treasure hunter (Knowledge cleric) Mardan Ferres, elven private investigator obsessed with that one unsolved murder (Assassin rogue) Xhekhetiel, halfling survivor of a Betrayer Gods cult (Runechild sorcerer/fighter)
@R3sistanceI agree with your point of view. It's also how I understand the relation between cantrips and prepared spells.
Basically, for me, it's like saying that cantrips are known and always prepared, while level 1+ spells can be prepared based on your class, as summarized in the table in Chapter 7.
Preparing Spells If you have a list of level 1+ spells you prepare, your spellcasting feature specifies when you can change the list and the number of spells you can change, as summarized in the Spell Preparation by Class table.
Cantrips always have similar text for all the classes:
Cantrips. You know [X] cantrips of your choice from ...
Also, as I read the Invocation, it seems to me that the spells are what's referred to as prepared, while the cantrips are assumed to be known (emphasis mine)
Cantrips and Rituals. When the book appears, choose three cantrips, and choose two level 1 spells that have the Ritual tag. The spells can be from any class’s spell list, and they must be spells you don’t already have prepared. While the book is on your person, you have the chosen spells prepared, and they function as Warlock spells for you.
As a side note, "known" also appears in the Improved Illusions feature from the Illusionist subclass:
Level 3: Improved Illusions
[...] You also know the Minor Illusion cantrip. If you already know it, you learn a different Wizard cantrip of your choice. The cantrip doesn’t count against your number of cantrips known.
@R3sistance Pact of the Tome isn't the only text that gives prepared cantrip, Celestial Patron, Circle of the Land (All), Circle of the Moon, Circle of the Sea, Circle of the Stars (Star Map), and Aberrant Sorcery. That 6 subclasses that prepare cantrips in someway for a total of 10 different ways (counting each land) or about 18% of all updated spell casting subclasses that have this wording. Celestial and Land use to have the level spells and extra cantrips as two different feature but were pushed together. Stars use to say you know the guidance cantrip but was simplified down. Aberrant was known but more to do with 2014 prepared cast vs known caster. Moon and sea are new.
So most of the problems come from combining cantrip and level +1 spells in the same text without thinking of what that could mean. All it would take is adding one line of text to always prepared spell rules to state that prepared cantrips are known but doesn’t count against your number of cantrips known to make it clearer.
Also, as I read the Invocation, it seems to me that the spells are what's referred to as prepared, while the cantrips are assumed to be known (emphasis mine)
Cantrips and Rituals. When the book appears, choose three cantrips, and choose two level 1 spells that have the Ritual tag. The spells can be from any class’s spell list, and they must be spells you don’t already have prepared. While the book is on your person, you have the chosen spells prepared, and they function as Warlock spells for you.
Oh. That's an interesting take and would mean that you have access to the Cantrips even without the tome, wouldn't it?
Also, as I read the Invocation, it seems to me that the spells are what's referred to as prepared, while the cantrips are assumed to be known (emphasis mine)
Cantrips and Rituals. When the book appears, choose three cantrips, and choose two level 1 spells that have the Ritual tag. The spells can be from any class’s spell list, and they must be spells you don’t already have prepared. While the book is on your person, you have the chosen spells prepared, and they function as Warlock spells for you.
Oh. That's an interesting take and would mean that you have access to the Cantrips even without the tome, wouldn't it?
Yeah, it's my personal bet if we consider spells in 2024 can be in two categories: cantrips as "known" and level 1+ spells as "prepared".
So, if all cantrips are "known", they're with you forever! :D
Yeah, it's my personal bet if we consider spells in 2024 can be in two categories: cantrips as "known" and level 1+ spells as "prepared".
So, if all cantrips are "known", they're with you forever! :D
This is not true as a general rule throughout all of 5e. It is just a somewhat consistent observation of how the currently published Spellcasting and Pact Magic class features are designed. If we consider all other ways in which a character might be given an ability to cast a spell, such as Species traits, Feats and other class features, these guidelines are not always followed. Sometimes a leveled spell becomes "learned"/"known". Sometimes a Cantrip becomes prepared without being "learned"/"known".
It appears spells you choose with Pact of the Tome are prepared cantrips you can cast despite not being known cantrip for your Warlock per se, making them ineligible with features affecting known cantrips specifically.
This is the best answer. If a prerequisite says that the spell must be known, then it's not good enough if the spell is (only) prepared. We can consider all known spells to be (always) prepared, but not all prepared spells are known.
Yeah, it's my personal bet if we consider spells in 2024 can be in two categories: cantrips as "known" and level 1+ spells as "prepared".
So, if all cantrips are "known", they're with you forever! :D
This is not true as a general rule throughout all of 5e. It is just a somewhat consistent observation of how the currently published Spellcasting and Pact Magic class features are designed. If we consider all other ways in which a character might be given an ability to cast a spell, such as Species traits, Feats and other class features, these guidelines are not always followed. Sometimes a leveled spell becomes "learned"/"known". Sometimes a Cantrip becomes prepared without being "learned"/"known".
Do you have any examples of levelled spells being "known/learned"? Some other examples of cantrips being prepared have already been mentioned.
When you reach character levels 3 and 5, you learn a higher-level spell, as shown on the table. You always have that spell prepared. You can cast it once without a spell slot, and you regain the ability to cast it in that way when you finish a Long Rest. You can also cast the spell using any spell slots you have of the appropriate level.
In this case, the spell is learned and then it also explicitly says that it's "always prepared". As far as I know, any spell or cantrip that is known/learned is automatically also "always prepared" (since knowing something means that it's stored in your mind / long-term memory or whatever -- so it's already "prepared in your mind"). But the general rules are a bit lacking when it comes to some of these things so it's good for the trait to explicitly mention it.
A better example might be the Warlock Eldritch Invocation called Pact of the Chain:
Pact of the Chain
You learn the Find Familiar spell and can cast it as a Magic action without expending a spell slot.
When you reach character levels 3 and 5, you learn a higher-level spell, as shown on the table. You always have that spell prepared. You can cast it once without a spell slot, and you regain the ability to cast it in that way when you finish a Long Rest. You can also cast the spell using any spell slots you have of the appropriate level.
In this case, the spell is learned and then it also explicitly says that it's "always prepared". As far as I know, any spell or cantrip that is known/learned is automatically also "always prepared" (since knowing something means that it's stored in your mind / long-term memory or whatever -- so it's already "prepared in your mind"). But the general rules are a bit lacking when it comes to some of these things so it's good for the trait to explicitly mention it.
A better example might be the Warlock Eldritch Invocation called Pact of the Chain:
Pact of the Chain
You learn the Find Familiar spell and can cast it as a Magic action without expending a spell slot.
So, it does come up here and there.
Thank you for the examples.
In the Elven Lineage scenario, it also says that you always have it prepared so "learning' the spell is not standing in for having it prepared. In Pact of the Chain, it states that you can cast it as a Magic action without a slot; you can basically cast it at will (provided you can supply the material component). So, again, it is not necessarily prepared and it is necessary to have it prepared to cast it (mechanically, the invocation turns it into a cantrip - except for effects that trigger of casting an actual cantrip).
I wonder if it is being used descriptively and not mechanically - if there are any scenarios where you depend on a levelled spell being "known" or "learned" in order to know if you can cast it without a second mechanic. Maybe I will research it further later - probably not, but maybe.
I can't tell if the discussion is starting to drift or not.
Posts #2 and #5 made the point that if a feature only says that a spell is prepared then such spells are not eligible to meet a prerequisite that specifically requires known cantrips. This is the best answer.
Some others then later suggested that cantrips are always known and that leveled spells are always prepared. But that's not a general rule. It's just something that happens to be true most of the time throughout all of the various specific rules for the various Spellcasting and Pact Magic class features.
Although I don't think that there's an explicit rule which says this, I believe that it's reasonable to assume that a known spell is automatically an "always prepared" spell, but not the other way around. Just because a spell is prepared doesn't make it a known spell.
The concept seems to be related to the ideas of short-term memory and long-term memory in real life. If there is a simple concept, I might permanently learn it such that it stays in long term memory. This can always be brought to my short-term memory at will. On the other hand, if I have to memorize a large volume of complex material, that might be like cramming for a final exam. This is then jammed into my somewhat limited short-term memory for use during the exam but is never really learned. Later, if I want to study for a different exam, I will have to brain dump this old information so that I can put something else into short-term memory instead. In this way, I am "preparing" for the exam but never truly "learning" the material. If I do somehow permanently learn the material, then it is always prepared for use in an exam and doesn't count against how much other information I can cram into my short-term memory for other exams.
[...] Although I don't think that there's an explicit rule which says this, I believe that it's reasonable to assume that a known spell is automatically an "always prepared" spell, but not the other way around. Just because a spell is prepared doesn't make it a known spell.
Do you have an example for this "Just because a spell is prepared doesn't make it a known spell"?
[...] Although I don't think that there's an explicit rule which says this, I believe that it's reasonable to assume that a known spell is automatically an "always prepared" spell, but not the other way around. Just because a spell is prepared doesn't make it a known spell.
Do you have an example for this "Just because a spell is prepared doesn't make it a known spell"?
There is not really any such thing as an "example" for this statement. Either there is an explicit rule which says this or there is not. I've already said that there is no such explicit rule. This is mainly because the words "known" and "learn" are never even mentioned anywhere in the Spells chapter (which is where the general spellcasting rules are written). So, these terms are not well defined by the game. Because of that, a DM must use the common English meaning of these words, along with the context clues that are given by how the rest of the game is written, in order to make an interpretation.
Here are some of the context clues that I am seeing:
-- The general rules require a spell to be "prepared in your mind" in order for you to be able to cast it.
-- The various Spellcasting class features are written such that they use the general rules for spellcasting with a certain category of spells: "See chapter 7 for the rules on spellcasting. The information below details how you use those rules with [Class] spells . . ."
-- Because these features use the general rules, they are not attempting to create specific exceptions to those rules -- they are attempting to conform to those rules. So, within these features, a spell must be "prepared in your mind" in order for you to be able to cast it.
-- Within these Spellcasting features, Cantrips are generally always referred to as "known" but never explicitly as "prepared". But because the general rules require a spell to be prepared . . . either we can never cast any Cantrip spells or we have to assume that a known spell is considered to be "always prepared", which makes logical sense given the common English meaning of the words "known" and "learned".
-- Within these Spellcasting features, Level 1+ spells are generally always referred to as "prepared" and never as "known", and the procedure for swapping prepared spells can often be performed a lot more frequently than the procedure for swapping known Cantrips (short-term vs long-term presence "in your mind"). However, the general rules do not require a spell to be known in order to cast it -- they only require that a spell is prepared. There is also no rule which explicitly says that a prepared spell is always a known spell. So, there is no rules-based reason to assume that a prepared spell must also be known. Various traits, Feats and features go out of their way to choose one of these terms or the other -- they are unlikely to be meant to be fully interchangeable.
Given this, we must now use the common English meanings as well as the context given by the rest of the rules to form an interpretation of "known/learned" vs "prepared". My interpretation is that knowing something in your mind is a more advanced version of something being prepared in your mind such that all known spells are prepared but not all prepared spells are known.
It would be helpful if the rules would make this more explicit somewhere.
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So Agonizing blast lets you do what its always done, only you have the option of having it apply to a different warlock spell rather than Eldritch blast as long as it's a "warlock cantrip" (it can be taken multiple times as well, tho I'm sure for technical reasons this is not reflected in platform) and Pact of the Tome lets you take a bunch of cantrips from whatever class and have them designated as "Warlock cantrip"
Is it thus reasonable to assume, that a player can take, say, "Shocking grasp" via Pact of the Tome, and apply Agonizing Blast to it? Or does this not work because of how that the cantrips gained from the Tome can be changed on a short rest? Such is to ask, does the invocation Agonizing Blast require warlock cantrips with permanence?
Agonizing Blast refers to "one of your known Warlock cantrips", while Pact of the Tome says you have those cantrips prepared. It's not 100% clear whether Agonizing Blast is using that term because they want to distinguish your permanent cantrips from the the rest, or if they're just sticking to convention (the rules rarely speak of cantrips as being prepared.)
One bit of circumstantial evidence in favor is that you could potentially swap out one of your "permanent" cantrips on level up and render Agonizing Blast temporarily unusable without ever messing with Pact of the Tome.
My gut feeling is that it's intended. The 2024 rules did away with the distinction between "known spells" and "prepared spells" for level 1+ spells in the various spellcasting classes; they're all just prepared spells now. Heck, Pact of the Tome has no issue saying that the spells you choose must be spells you don't have prepared already, which would include the cantrips too. I'm not sure why they've continued to use the "you learn/know" terminology for cantrips despite that, but I don't think it's meant to denote a distinct thing.
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In my opinion, yes. I already gave my thoughts in the thread Does Lessons of the first ones, Agonizing blast, and Magic initiate (Druid) work together to create the best melee weapon?:
In fact, Ray of Frost was mentioned in the next video (around 9:44): New Warlock | 2024 Player's Handbook | D&D (youtube.com)
I think this could have been fixed if the cantrip that Agonizing Blast is being used on could be changed on a long rest.
Technically all spells from Pact of the Tome are Warlock spells and so the cantrips would be Warlock Cantrip, thus I'd say it works but you can only benefit from this benefit while you have the cantrip available from Pact of the Tome and it is cast as a Warlock spell using Warlock's spell attack modifier (Charisma).
It appears spells you choose with Pact of the Tome are prepared cantrips you can cast despite not being known cantrip for your Warlock per se, making them ineligible with features affecting known cantrips specifically.
Man, I watched this video and totally forgot this was discussed. Thanks for bringing it up.
This makes perfect sense, I'll be borrowing this advice.
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I decided to have a re-read and decided to focus on the word known. Known is not properly defined from what I can see, it's mentioned once in pact magic, that at level 1 you know 2 cantrips and then you learn more at levels 4 and 10.
The spells from pact of the tome are prepared but no mention of known.
Checking other classes, it would appear that levelled spells are prepared and cantrips are known, so this seems more likely to be an oversight in that it should say the cantrips from book of the tome are known, as cantrips are never prepared. This could be wrong of course, but looking at other features and feats that add cantrips like Magic Initiate and Blessed Warrior, these also say "learned" as opposed to "prepared".
RAW I'd have to agree with you , nothing says you "know" the cantrip from pact of the tome but I don't see any other cases of cantrips being "prepared", which is what pact of the tome implies, so I'd say RAI is that all cantrips must be known to be cast and thus count as known while holding the pact of the tome.
More so given this part of pact magic:
While it comes from an invocation, eldritch invocation itself is a Warlock Feature and similar text disappeared from Pact of the Tome from 2014 to 2024, likely because it's now already essentially covered in the Pact Magic feature itself.
Overall, it's another unclear and inconcise area of 2024.
This would pretty much make the Repeatable portion of the invocation irrelevant, but I'm not sure how often people will actually take it more than once anyway. (Maybe a character with one melee cantrip and one ranged cantrip that both see frequent usage)
Active characters:
Carric Aquissar, elven wannabe artist in his deconstructionist period (Archfey warlock)
Lan Kidogo, mapach archaeologist and treasure hunter (Knowledge cleric)
Mardan Ferres, elven private investigator obsessed with that one unsolved murder (Assassin rogue)
Xhekhetiel, halfling survivor of a Betrayer Gods cult (Runechild sorcerer/fighter)
@R3sistance I agree with your point of view. It's also how I understand the relation between cantrips and prepared spells.
Basically, for me, it's like saying that cantrips are known and always prepared, while level 1+ spells can be prepared based on your class, as summarized in the table in Chapter 7.
Cantrips always have similar text for all the classes:
Also, as I read the Invocation, it seems to me that the spells are what's referred to as prepared, while the cantrips are assumed to be known (emphasis mine)
As a side note, "known" also appears in the Improved Illusions feature from the Illusionist subclass:
Oh, it's an honor! :)
@R3sistance Pact of the Tome isn't the only text that gives prepared cantrip, Celestial Patron, Circle of the Land (All), Circle of the Moon, Circle of the Sea, Circle of the Stars (Star Map), and Aberrant Sorcery. That 6 subclasses that prepare cantrips in someway for a total of 10 different ways (counting each land) or about 18% of all updated spell casting subclasses that have this wording. Celestial and Land use to have the level spells and extra cantrips as two different feature but were pushed together. Stars use to say you know the guidance cantrip but was simplified down. Aberrant was known but more to do with 2014 prepared cast vs known caster. Moon and sea are new.
So most of the problems come from combining cantrip and level +1 spells in the same text without thinking of what that could mean. All it would take is adding one line of text to always prepared spell rules to state that prepared cantrips are known but doesn’t count against your number of cantrips known to make it clearer.
Oh. That's an interesting take and would mean that you have access to the Cantrips even without the tome, wouldn't it?
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Yeah, it's my personal bet if we consider spells in 2024 can be in two categories: cantrips as "known" and level 1+ spells as "prepared".
So, if all cantrips are "known", they're with you forever! :D
This is not true as a general rule throughout all of 5e. It is just a somewhat consistent observation of how the currently published Spellcasting and Pact Magic class features are designed. If we consider all other ways in which a character might be given an ability to cast a spell, such as Species traits, Feats and other class features, these guidelines are not always followed. Sometimes a leveled spell becomes "learned"/"known". Sometimes a Cantrip becomes prepared without being "learned"/"known".
This is the best answer. If a prerequisite says that the spell must be known, then it's not good enough if the spell is (only) prepared. We can consider all known spells to be (always) prepared, but not all prepared spells are known.
Do you have any examples of levelled spells being "known/learned"? Some other examples of cantrips being prepared have already been mentioned.
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The Elf trait "Elven Lineage" has that wording:
In this case, the spell is learned and then it also explicitly says that it's "always prepared". As far as I know, any spell or cantrip that is known/learned is automatically also "always prepared" (since knowing something means that it's stored in your mind / long-term memory or whatever -- so it's already "prepared in your mind"). But the general rules are a bit lacking when it comes to some of these things so it's good for the trait to explicitly mention it.
A better example might be the Warlock Eldritch Invocation called Pact of the Chain:
So, it does come up here and there.
Thank you for the examples.
In the Elven Lineage scenario, it also says that you always have it prepared so "learning' the spell is not standing in for having it prepared. In Pact of the Chain, it states that you can cast it as a Magic action without a slot; you can basically cast it at will (provided you can supply the material component). So, again, it is not necessarily prepared and it is necessary to have it prepared to cast it (mechanically, the invocation turns it into a cantrip - except for effects that trigger of casting an actual cantrip).
I wonder if it is being used descriptively and not mechanically - if there are any scenarios where you depend on a levelled spell being "known" or "learned" in order to know if you can cast it without a second mechanic. Maybe I will research it further later - probably not, but maybe.
How to add Tooltips.
I can't tell if the discussion is starting to drift or not.
Posts #2 and #5 made the point that if a feature only says that a spell is prepared then such spells are not eligible to meet a prerequisite that specifically requires known cantrips. This is the best answer.
Some others then later suggested that cantrips are always known and that leveled spells are always prepared. But that's not a general rule. It's just something that happens to be true most of the time throughout all of the various specific rules for the various Spellcasting and Pact Magic class features.
Although I don't think that there's an explicit rule which says this, I believe that it's reasonable to assume that a known spell is automatically an "always prepared" spell, but not the other way around. Just because a spell is prepared doesn't make it a known spell.
The concept seems to be related to the ideas of short-term memory and long-term memory in real life. If there is a simple concept, I might permanently learn it such that it stays in long term memory. This can always be brought to my short-term memory at will. On the other hand, if I have to memorize a large volume of complex material, that might be like cramming for a final exam. This is then jammed into my somewhat limited short-term memory for use during the exam but is never really learned. Later, if I want to study for a different exam, I will have to brain dump this old information so that I can put something else into short-term memory instead. In this way, I am "preparing" for the exam but never truly "learning" the material. If I do somehow permanently learn the material, then it is always prepared for use in an exam and doesn't count against how much other information I can cram into my short-term memory for other exams.
Do you have an example for this "Just because a spell is prepared doesn't make it a known spell"?
There is not really any such thing as an "example" for this statement. Either there is an explicit rule which says this or there is not. I've already said that there is no such explicit rule. This is mainly because the words "known" and "learn" are never even mentioned anywhere in the Spells chapter (which is where the general spellcasting rules are written). So, these terms are not well defined by the game. Because of that, a DM must use the common English meaning of these words, along with the context clues that are given by how the rest of the game is written, in order to make an interpretation.
Here are some of the context clues that I am seeing:
-- The general rules require a spell to be "prepared in your mind" in order for you to be able to cast it.
-- The various Spellcasting class features are written such that they use the general rules for spellcasting with a certain category of spells: "See chapter 7 for the rules on spellcasting. The information below details how you use those rules with [Class] spells . . ."
-- Because these features use the general rules, they are not attempting to create specific exceptions to those rules -- they are attempting to conform to those rules. So, within these features, a spell must be "prepared in your mind" in order for you to be able to cast it.
-- Within these Spellcasting features, Cantrips are generally always referred to as "known" but never explicitly as "prepared". But because the general rules require a spell to be prepared . . . either we can never cast any Cantrip spells or we have to assume that a known spell is considered to be "always prepared", which makes logical sense given the common English meaning of the words "known" and "learned".
-- Within these Spellcasting features, Level 1+ spells are generally always referred to as "prepared" and never as "known", and the procedure for swapping prepared spells can often be performed a lot more frequently than the procedure for swapping known Cantrips (short-term vs long-term presence "in your mind"). However, the general rules do not require a spell to be known in order to cast it -- they only require that a spell is prepared. There is also no rule which explicitly says that a prepared spell is always a known spell. So, there is no rules-based reason to assume that a prepared spell must also be known. Various traits, Feats and features go out of their way to choose one of these terms or the other -- they are unlikely to be meant to be fully interchangeable.
Given this, we must now use the common English meanings as well as the context given by the rest of the rules to form an interpretation of "known/learned" vs "prepared". My interpretation is that knowing something in your mind is a more advanced version of something being prepared in your mind such that all known spells are prepared but not all prepared spells are known.
It would be helpful if the rules would make this more explicit somewhere.