ceigered:Isn't there also "Vere, vi petu ke via kuracisto .... ....."?
I've seen that sort of usage in English and other non Indo European languages too, using an infinitive construction instead of "should", although I imagine it comes of more familiar than "devus", but for some probably gives them less headaches than trying to figure out why "dev-" is in the conditional tense

"Devus" surely doesn't mean 'should', does it?! I would translate the sentence thus:

Vi devUs peti al la kuracisto = You would have to ask the doctor.

Chainy:When you search for 'should' in the Lernu dictionary, it comes up with 'devi'. Oh no, that is surely wrong?! Or can someone come up with an explanation?

On ReVo, for the definition for "devi", the second definition is this:

ReVo:Kelkfoje ĝi montras la certecon aŭ eĉ nur la probablecon; certe ...i, probable ...i, supozeble ...i:

(Sometimes it shows the certainty or even only the probability; certainly must, probably must, supposedly must)

So maybe "devi" does translate to "should", but in the sense of say "The sun must rise in the morning... shouldn't it?" (or maybe "Ĝi devas alveni je la tria horo, sed se ne, vi devus iri kaj serĉi ĝin..." - It should arrive at 3 o'clock, but if not, you must go and search for it).

I think the confusion with the must/should distinction is that there is sometimes a sort of volitive/opinionative nuance to the meaning, crossing between "devi", "voli (ke)" and "pensas/opinias (ke)", and so when we use "devi" alone for "should", that meaning suddenly is implied and no longer represented by something, leading to people feeling as if something is amiss... Anyway, Erinja's usage looks best so maybe it's fair to use that to lighten the load for "devi", so to speak

Esperanto doesn't have an exact equivalent for "should". Devus is a commonly used approximation. For example Vi devus peti vian kuraciston kontroli tion, "You should ask your doctor to check that".

Polaris, I believe your initial analysis would be correct. Both "devi" (to have to), and "povi" (to be able to), when used with the "us" ending, makes these verbs imply something that is less than certain.

Li devus viziti la kuracisto
He should visit the doctor

as opposed to
Li devas viziti la kuracisto
He has to (must) visit the doctor

In the same way, the verb povi could also mean "could" in the sense of "might"
Mi povus labori morgaŭ
I could (might) work tomorrow.

Also, perhaps the negatives could be handled thusly:

Li ne povu iri al la urbego.
He must not go to the city.

Li ne povus iri al la urbego.
He should not go to the city.

Li ne bezonas iri al la urbego.
He doesn't have to (need to) go to the city.

angel32163:Also, perhaps the negatives could be handled thusly:

Li ne povu iri al la urbego.
He must not go to the city.

Li ne povus iri al la urbego.
He should not go to the city.

Li ne bezonas iri al la urbego.
He doesn't have to (need to) go to the city.

I'd say like this:

Li ne rajtas iri al la urbo.
He must not go into town.

Li ne iru al la urbo.
He should not go into town.

Li ne bezonas iri into town.
He does not need to go into town.

Generally for "He should go..." I'd say "Li iru ..."

Johannes

angel32163:Also, perhaps the negatives could be handled thusly:

Li ne povu iri al la urbego.
He must not go to the city.

Li ne povus iri al la urbego.
He should not go to the city.

Li ne bezonas iri al la urbego.
He doesn't have to (need to) go to the city.

If I'm understanding right, "li ne povu iri al la urbego" is like saying "may he not be able to go to the city"--as in, expressing a wish or a hope on your part.

The second one, "li ne povus iri al la urbego" sounds like "he wouldn't be able to go to the city" (as in, if something else weren't happening, he couldn't go).

Polaris:

angel32163:Also, perhaps the negatives could be handled thusly:

Li ne povu iri al la urbego.
He must not go to the city.

Li ne povus iri al la urbego.
He should not go to the city.

Li ne bezonas iri al la urbego.
He doesn't have to (need to) go to the city.

If I'm understanding right, "li ne povu iri al la urbego" is like saying "may he not be able to go to the city"--as in, expressing a wish or a hope on your part.

The second one, "li ne povus iri al la urbego" sounds like "he wouldn't be able to go to the city" (as in, if something else weren't happening, he couldn't go).

Correct.

Polaris:If I'm understanding right, "li ne povu iri al la urbego" is like saying "may he not be able to go to the city"--as in, expressing a wish or a hope on your part.

Which is still approximately equal to "should", as "should" in this case expresses one's opinion of sorts.

Sorry, ignore my ignorance, didn't read have the conversation

Chainy:"Devus" surely doesn't mean 'should', does it?! I would translate the sentence thus:

Vi devUs peti al la kuracisto = You would have to ask the doctor.

You would have to ask the doctor = you should ask the doctor.
Compare:
"I don't know if you're sick, you would have to ask the doctor"
with
"I don't know if you're sick, you should ask the doctor"
So there's no difference.

After some thinking about this, "would have to" and "should" mean the same thing in this context - "would" is the conditional form of "will", and "should" is the conditional form of "shall", but here it seems that "should" carries a sort of opiniative meaning without needing to use "must" due to some traditional idiosyncracies seen here:

Normal traditional simple future tense:
I/We shall, but for all other persons, you/he/she/they will

The emphatic future tense, with the sense of "must":
I/We will, but for all other persons, you/he/she/they shall.

Esperanto lacks this traditional use of emphasis (and modern English only uses it in the conditional form, and just doesn't care about shall otherwise) by the looks of things, thus why "devus" can make do for so many occasions.

(some interesting cognates to the English usage of "shall/should":
Norwegian
Dutch
In these languages, the idea seems to be to phrase things as if the speaker is hypothetically in the future, and then comment on what their future actions in the past would have been, as if to sound more sure and authoritative about those past opinions.

While in the Germanic languages, the conditional has been eroded away, in Esperanto, there is a conditional tense which allows the speaker to talk hypothetically about what their actions would or would not be in a situation, which might be related to why such a round about method of translating "should" and "must" is used).

ceigered:
While in the Germanic languages, the conditional has been eroded away

Not really. The German "Konjunktiv" is something extremely similar to the Esperanto conditional, and it's still in use although many speakers don't use it often on non-modal verbs and prefer to use würde or täte (analogously to English would). That's probably because in regular verbs, the conjunctive form is the same as the imperfect form.

English has preserved this form only in should and could.

(Okay, I know I'm off-topic, sorry for that.)