yyaann:I have sometimes seen proper names with adjective ending added to them to sort of make up for the lack of genitive case.

La Bob-a domo -> Bob's house
La Peter-a libro -> Peter's book
La Anna-a patro -> Anna's father

This usage with proper names is strongly discouraged for exactly the reason you mention, with ambiguity. Petera libro - is it a book belonging to him? did he write the book? is the book about him?

Anna-a patro - it is a father belonging to Anna? A father with similar characteristics to Anna's?

This usage is a terrible idea.

For me, I'm quite happy with the standard Esperanto manner of showing possession, but I constantly get caught out. For example in a sentence like:

"It was Peter's fault," I try to recast it in my mind as something like: "Peter was at fault", but then hesitate over how to formulate a sentence like that because I can't translate "at fault".

Petro estis kulpa isn't right because it is "Peter was guilty" and that's not quite the same thing. So it must be: "Estis la kulpo de Petro". But I feel there's something missing because the sentence feels basic and less nuanced than saying "at fault".

It's a jolt for me having to recast such sentences all the time.

erinja:Petera libro - is it a book belonging to him? did he write the book? is the book about him?

Anna-a patro - it is a father belonging to Anna? A father with similar characteristics to Anna's?

This usage is a terrible idea.

I think it's all about using judgement. Is the context clear? Is the audience likely to understand? Does using this form add a humorous/litterary/playful or otherwise interesting effect that does not significantly compromise clarity?

I've seen writers such as Claude Piron use this form and when they did, what they meant was always clear. Of course, they knew to use it with parsimony.

Getting back to a specific example, if la libro de Peter has already been mentioned, then referring to it as la Petera libro a few sentences afterwards should not hinder comprehension.

erinja:

yyaann:

La Peter-a libro -> Peter's book
La Anna-a patro -> Anna's father

This usage with proper names is strongly discouraged for exactly the reason you mention, with ambiguity. Petera libro - is it a book belonging to him? did he write the book? is the book about him?

Isn't it the same problem with la libro de Petro? Does he own the book, did he write the book or is the book about him? I suppose you would use la libro pri Petro for the last phrase but if you think of de as the English word of it could be translated to the book of Peter

erinja:Anna-a patro - it is a father belonging to Anna? A father with similar characteristics to Anna's?

Although here, I see a different situation.

erinja:

yyaann:I have sometimes seen proper names with adjective ending added to them to sort of make up for the lack of genitive case.

La Bob-a domo -> Bob's house
La Peter-a libro -> Peter's book
La Anna-a patro -> Anna's father

This usage with proper names is strongly discouraged for exactly the reason you mention, with ambiguity. Petera libro - is it a book belonging to him? did he write the book? is the book about him?

Anna-a patro - it is a father belonging to Anna? A father with similar characteristics to Anna's?

This usage is a terrible idea.

I would go even further and say that this usage isn't Esperanto anymore.

Esperanto has three ways of expressing possession (actual or metaphorical):
- The ending -es of the correlatives (kies, ties, ies, nenies, ĉies).
- The possessive adjective of the personal pronouns (mia, cia, lia, ŝia, ĝia, onia, sia, nia, via, ilia).
- The preposition de for the rest.

If we start using "la Anaa patro" instead of "la patro de Ana", we could also start using "Anaes patro".

Without doubt it is possible to derive adjectives from proper names same as in English:

La Newtonaj leĝoj pri movado.
Freuda misvortigo.
Bohra atommodelo.

But these are still adjectives and not possessives, as in English Newtonian, Freudian, etc.

nornen:
Without doubt it is possible to derive adjectives from proper names same as in English:

La Newtonaj leĝoj pri movado.
Freuda misvortigo.
Bohra atommodelo.

But these are still adjectives and not possessives, as in English Newtonian, Freudian, etc.

Neŭtonaj leĝoj
Freŭda misvortigo.
Bora atommodelo.
If you add Esperantic -a, you must also Esperantize the root.

sergejm:

nornen:
Without doubt it is possible to derive adjectives from proper names same as in English:

La Newtonaj leĝoj pri movado.
Freuda misvortigo.
Bohra atommodelo.

But these are still adjectives and not possessives, as in English Newtonian, Freudian, etc.

Neŭtonaj leĝoj
Freŭda misvortigo.
Bora atommodelo.
If you add Esperantic -a, you must also Esperantize the root.

Then it should be "Frojda" and not "Freŭda".

nornen:Then it should be "Frojda" and not "Freŭda".

My dictionary freŭdisto - фрейдист.

It's Freŭda (Freudian) in my Wells dictionary too.