Book of Ancient Secrets - Ritual spells

Quote from select_hero >> 

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That is all. Everyone has the ability to copy from a wizard scroll or from spell books. The general rule is on p. 292

"A wizard spell on a spell scroll can be copied just as spells in spellbooks can be copied [costing 50 gp and taking 2 hours per level]. When a spell is copied from a spell scroll, the copier must succeed on an Intelligence (Arcana) check with a DC equal to 10 + the spell’s level. If the check succeeds, the spell is successfully copied. Whether the check succeeds or fails, the spell scroll is destroyed."

This Invocation seems to extend that ability for Warlocks to any spell with a ritual tag, adding permanent ritual spells to their Tome.

 
Is that sentence in bold right?

As far as I know, not everyone can copy spells into spellbooks—only Wizards have this ability. And Warlocks if they follow the rules outlined in the Book of Ancient Secrets feature.

In fact, RAW: "a wizard spell on a spell scroll can be copied just as spells in spellbooks can be copied [...] the copier must succeed on an Intelligence (Arcana) check [...]" (DMG p. 200)

While that phrase might suggest that only wizard spells from (consumable) spell scrolls can be copied with a successful Intelligence (Arcana) check, RAI is that warlocks, being able to copy any spell, should have the capability to copy spells from any scroll, whether it's a consumable spell scroll or a regular piece of paper with a scroll written on it.

Anyone that is proficient with Arcana.  

Quote from Mog_Dracov >>

Anyone that is proficient with Arcana.  

Is that rule from the core books or Xanathar's Guide to Everything? Do you happen to have the page numbers for that rule in the core books?

Anyway, being proficient with Arcana shouldn't be enough. The character must have the spell prepared/known.

I don't have the page number, but it's in the Downtime Revisited section of XGtE. The character needs to be proficient in Arcana, have any material components required for the spell, and must either have it as a known spell or a prepared spell. There's a table that goes into cost/time per level of spell.

Quote from Rallozar >>

I don't have the page number, but it's in the Downtime Revisited section of XGtE. The character needs to be proficient in Arcana, have any material components required for the spell, and must either have it as a known spell or a prepared spell. There's a table that goes into cost/time per level of spell.

Ok, then the sentence I mentioned in bold was not right: "Everyone has the ability to copy from a wizard scroll or from spell books." 

Actually, upon closer inspection, that sentence isn't right at all. What I took from Xanathar's is how to create a scroll from scratch, not copying from one. The only people that can do that are Wizards, characters with the Ritual Caster feat, and Warlocks with Book of Ancient Secrets. Even then, they copy it into their books first before making a new scroll.

Quote from Rallozar >>

Actually, upon closer inspection, that sentence isn't right at all. What I took from Xanathar's is how to create a scroll from scratch, not copying from one. The only people that can do that are Wizards, characters with the Ritual Caster feat, and Warlocks with Book of Ancient Secrets. Even then, they copy it into their books first before making a new scroll.

I agree with you, based on my understanding of the rules. In case anyone is interested, I asked this question not too time ago: Which classes can transcribe spells into a non-magical piece of paper?

PS. I've updated my previous answer because I wrote something that wasn't right... I was very sleepy.

Ok, let's say I have the Keen Mind feat, eyes of the rune keeper, identify, and eldritch sight... could I use a combination of all that (touching the ritual site for identify), to scribe a ritual i saw performed -with the knowledge of the original caster helping me, into the book of ancient secrets this way?

Quote from rasonage >>

Ok, let's say I have the Keen Mind feat, eyes of the rune keeper, identify, and eldritch sight... could I use a combination of all that (touching the ritual site for identify), to scribe a ritual i saw performed -with the knowledge of the original caster helping me, into the book of ancient secrets this way?

 Ask your DM. The rules themselves don't give you any way to do so, but this kind of combining abilities and using the narrative to do things not provided for by the rules is generally encouraged.

@rasonage Just in case it could be useful for your question, here are a couple of posts from a thread I remember about Keen Mind:

Quote from The_Ace_of_Rogues >>

As a general rule of thumb, the answer to "can this feature that tangentially relates to text information or ink bypass the printed requirements for scribing a spell in a spellbook" is "no"; the description of the components is a mixture of abstraction of the concept of applied research and fluff while the time, cost, and source requirements are RAW. Only the Wizard subclass features that explicitly refer to points in the process alter that process. Anything that doesn't explicitly say it alters the process does not, by RAW.

One common bit about spell scrolls is that what's written on the scroll is the equivalent of shorthand or an executable derived from a source code- anyone who meets whatever requirements are set by the edition can pick the scroll up and use it because most of the work has been done ahead of time. You can think of the Arcana check you make as attempting to reverse engineer the setup from running the effect of the spell in a controlled way.

Basically, what's written on a spell scroll is not the same as the entire formula you'd find in a spellbook.

Quote from Tarod_ >>

I agree with the answers given. Just to add here a tweet from the Dev (link to sageadvice.eu):

@attacop Does a wizard with the Keen Mind feat have unrestricted prepared spells?
@JeremyECrawford The Keen Mind feat isn't meant to change how a wizard's spell preparation works.

And this one (link to sageadvice.eu) from Matthew Mercer (Critical Role), just for curious readers:

@GaiGazimon How do you balance Keen Mind with Wizards? By reading what Keen Mind does, it would allow for a Wizard to just see a spell being used and then can use it themselves.
@matthewmercer There is MUCH MORE to casting a spell beyond a gesture and a sound. The mind of the mage has memorized elaborate equations and glyphs they weave in their mind’s eye as they cast it. Just seeing a spell be cast wouldn’t enable you to.