horsto:la urbo trovas sin en Usono.

Well, we find this construction in the Fundamento (Ekzercaro §25):

Sur la kameno inter du potoj staras fera kaldrono; el la kaldrono, en kiu sin trovas bolanta akvo, eliras vaporo; tra la fenestro, kiu sin trovas apud la pordo, la vaporo iras sur la korton.

And in §26:

Super la tero sin trovas aero.

La hirundo flugis trans la riveron, ĉar trans la rivero sin trovis aliaj hirundoj.

And some more - so at least in earlier times sin trovi was a common way to express today's troviĝi. Today troviĝi is more common.

But it's completely different in the case of: la kato laviĝis.
For me that is a poor and lazy way to express the situation: You know what happens, but you express that in a way that doesn't allow the reader to understand exactly what happens.

Yes, I admit to that. It wasn't feline sanitation, but the scope of the -iĝi construction that interested me, and I chose a bad example. I agree that "La kato lavis sin," is the better sentence.

This would translate to English as "the cat washed", which in practice would be interpreted as the cat washed itself.

Now I see what you mean. Like "Mi moviĝis," for "I moved." It's those ergative verbs that give me trouble. As I understand them, the verbs of the form (transitive stem + iĝi) should not show direct agency. If am riding in a car, or skydiving, then "Mi moviĝas." But if I am dancing, then "Mi movas sin." Some sources bear me out, but others don't.

arkadio:"Mi movas sin."

No, if the subject is not in the third person, you don't use sin but the subject's pronoun. Thus, mi movas min and not *mi movas sin.

horsto:la kato laviĝis.
For me that is a poor and lazy way to express the situation: You know what happens, but you express that in a way that doesn't allow the reader to understand exactly what happens.

It's not always necessary to be completely precise though. I can agree it would be a poor choice if it's not clear from context which sense is meant. When it is clear though I don't see a problem in it. I think it's nice to be able to preserve the middle-voice forms that are present in national languages, although like you I incline towards the accusative method in general because of its greater precision.

The same ambiguity does exist with verbs like troviĝi but they rarely cause a problem. For example from La Faraono we have:

El la banejo ĉiuj tri iris inter la arboj: pasinte kelke da ĝardenoj, ili fine troviĝis sur malplena placo.

In the above "trovis sin" could have worked just as well but "troviĝis" is still perfectly well understood to mean the same thing because the context doesn't suggest it's other people finding them there.

In the same way laviĝi and baniĝi are often very well understood to mean lavi sin and bani sin respectively. If there's some confusion caused by the presence of people who might be perceived as the washer or bather of the subject, then of course the accusative usage is preferable. In practice I don't see this happen all that often though.

darkweasel:

arkadio:"Mi movas sin."

No, if the subject is not in the third person, you don't use sin but the subject's pronoun. Thus, mi movas min and not *mi movas sin.

Yes. Thanks. That was just an oversight.

Off topic, but I find a great way to remember "Mi .... min" is to remember that the same construction is in Swedish and French:
"Jag lär mig lite Svenska" (I teach myself a little Swedish)
"Je m'appelle ......" (or spelt similarly: I-myself-call (name))

(Not aimed at arkadio but rather at anyone else reading and going "wha? Why not use sin?" (simply because its fairly unnatural)).

ceigered:Off topic, but I find a great way to remember "Mi .... min" is to remember that the same construction is in Swedish and French:
"Jag lär mig lite Svenska" (I teach myself a little Swedish)
"Je m'appelle ......" (or spelt similarly: I-myself-call (name))

(Not aimed at arkadio but rather at anyone else reading and going "wha? Why not use sin?" (simply because its fairly unnatural)).

As well as in German and even English (sin = himself, herself, itself, themselves).

tommjames:

horsto:la kato laviĝis.
For me that is a poor and lazy way to express the situation: You know what happens, but you express that in a way that doesn't allow the reader to understand exactly what happens.

It's not always necessary to be completely precise though. I can agree it would be a poor choice if it's not clear from context which sense is meant. When it is clear though I don't see a problem in it. I think it's nice to be able to preserve the middle-voice forms that are present in national languages, although like you I incline towards the accusative method in general because of its greater precision.

You're right, I forgot to add this:
If you yourself are not sure about what happened, for example if you saw the cat before and it was dirty and you see it now and it is clean, but you don't know if it was washed or if it washed itself, then the iĝ-form perfectly expresses this uncertainty: la kato (iel) laviĝis

Thanks all for your replies. I found the source of the examples I'd paraphrased. From J.C. Wells' Esperanto-English dictionary. From page 18:
(1) We sold a lot of books. Ni vendis multajn librojn.
(2) The books sold well. La librojn bone vendiĝis.
On the next page he gives examples of English ambiguity that doesn't arise in Esperanto:
(3) Publicity booklets sell.
(3a) Informbroŝuroj vendas (varojn).
(3b) Informbroŝuroj vendiĝas.
And:
(4) Children don't wash readily.
In Esperanto, this could be
(4a) Infanoj ne volonte lavas sin.
(4b) Infanoj ne volonte laviĝas.
(4c) Infanoj ne volonte lavas (tolaĵojn).
The meanings of 3a and 3b are clear. What about 4b? By juxtaposing 4a and 4b, Wells seems to me to be differentiating them semantically. Is he implying (like Ivy Kellerman) that with a (transitive stem + iĝi) verb the subject should be considered the logical object? Or does he just mean that 4b is more general than 4a?

arkadio:The meanings of 3a and 3b are clear. What about 4b? By juxtaposing 4a and 4b, Wells seems to me to be differentiating them semantically.

They are different in that 4a definitely shows it's the child washing itself, whereas 4b is more general, as discussed in previous posts. Of course 4b could mean exactly the same as 4a in practice.

arkadio:Is he implying (like Ivy Kellerman) that with a (transitive stem + iĝi) verb the subject should be considered the logical object?

I don't know if he's implying that, but it's certainly the case that the subject of an iĝ verb becomes the logical object. PMEG explains that thusly:

PMEG:Ĉe IĜ-verbo farita el objekta verbo la subjekto estas la objekto de la origina verbo. Ĉe tiaj ĉi verboj IĜ do servas por renversi la frazrolojn.

Translated: With an iĝ-verb made out of a transitive verb the subject is the object of the original verb. With these kinds of verbs iĝ serves to reverse the roles.