Miaj ekzemploj :

Vi ne devas mortigi iun
Vi devus legi tion (konsilo)

Ĉu mi devus fari tion ? (supozo, necertaĵo, futuro, ebleco, persona elekto)

Ĉu mi devas fari tion ? (necertaĵo, kolektiva ordo, regado, nune)

I've just come across this example of 'devOs' in one of the Lernu pages:

First the text talks about the possibility of taking an exam in Esperanto and then it says: "Zorge tralerninte tiun ĉi libron kaj leginte la necesan literaturon, vi devos esti kapabla por tio." (Having carefully learned [the material in] this book and after reading the necessary literature, you should be capable of doing this [exam].)

"DevOs" certainly seems to mean 'should' here. It really does seem like all the forms of 'devi' can either have the meaning of 'should' or 'must'. Only the context hints at one or the other, or you have to add extra words in there to make it clear that you mean 'must'...

I'd really like to know the pattern, work out when to use 'devas', 'devos' or 'devus'... I wonder if this is at all possible?!

Frankouche:Miaj ekzemploj :

Vi ne devas mortigi iun
Vi devus legi tion (konsilo)

Ĉu mi devus fari tion ? (supozo, necertaĵo, futuro, ebleco, persona elekto)

Ĉu mi devas fari tion ? (necertaĵo, kolektiva ordo, regado, nune)

thank you, frankouche. I'll have to think about these examples tomorrow evening. Need some sleep now..

Miaj ekzemploj :

Vi ne devas mortigi iun
Vi devus legi tion (konsilo)

Ĉu mi devus fari tion ? (supozo, necertaĵo, futuro, ebleco, persona elekto)

Ĉu mi devas fari tion ? (necertaĵo, kolektiva ordo, regado, nune)

Frankouche, how you've used "devus/devas" in these examples is how I would use them.
I read these as:

You must not kill anyone.
You should read that. or - You ought to read that.
Should I do that?
Do I have to do that?

Chainy:I've just come across this example of 'devOs' in one of the Lernu pages:

First the text talks about the possibility of taking an exam in Esperanto and then it says: "Zorge tralerninte tiun ĉi libron kaj leginte la necesan literaturon, vi devos esti kapabla por tio." (Having carefully learned [the material in] this book and after reading the necessary literature, you should be capable of doing this [exam].)

"DevOs" certainly seems to mean 'should' here.

It means "must" in this context, future tense. This sentence would be translated into English using should, but only because there isn't a convenient and elegant way to express a future tense of "must". The sentence is saying that if you have read this book carefully and read the necessary literature, it must be the case that you will successfully pass this exam.

angel32163:Frankouche, how you've used "devus/devas" in these examples is how I would use them.
I read these as:

You must not kill anyone.
You should read that. or - You ought to read that.
Should I do that?
Do I have to do that?

Certainly.

In fact, it's difficult for me to know how to say it correctly in english, even if i can guess if it's incorrect.

In Esperanto, like in French, devas/devus is the same verb ("devoir") and works the same, so it's easy to express it (except the volitive form "devu", that i rarely use).

One of the first thing, i thought curious when i learned english, is those forms : must, may, might, to have to, would & should, that we can sometimes express in French with only one verb.
I use them in english very carefully.

Maybe, that's why "devas/devus", seems to be diffult for english speakers.

erinja:

Chainy:I've just come across this example of 'devOs' in one of the Lernu pages:

First the text talks about the possibility of taking an exam in Esperanto and then it says: "Zorge tralerninte tiun ĉi libron kaj leginte la necesan literaturon, vi devos esti kapabla por tio." (Having carefully learned [the material in] this book and after reading the necessary literature, you should be capable of doing this [exam].)

"DevOs" certainly seems to mean 'should' here.

It means "must" in this context, future tense. This sentence would be translated into English using should, but only because there isn't a convenient and elegant way to express a future tense of "must". The sentence is saying that if you have read this book carefully and read the necessary literature, it must be the case that you will successfully pass this exam.

Ok, I think I know what you mean there.

How about a sentence like this:

"You missed a great party last night. You should have come"

How would we say that in Esperanto?

I've just discovered the word 'devintus'... (estus devinta). Would that be suitable for my question above?!

You should have come = Vi devintus veni?!

Seems you can do the same kind of thing with 'povus' and 'volus', changing to 'povintus' and 'volintus'...

But then, how would you say 'You missed a great party?' Maybe, 'Vi preterpasis bonegan feston'?! Any ideas?

Chainy:I've just discovered the word 'devintus'... (estus devinta). Would that be suitable for my question above?!

You should have come = Vi devintus veni?!

Seems you can do the same kind of thing with 'povus' and 'volus', changing to 'povintus' and 'volintus'...

But then, how would you say 'You missed a great party?' Maybe, 'Vi preterpasis bonegan feston'?! Any ideas?

There's been a prior discussion on "Vi devintus veni" before here, I can't remember the details but controversy aside it works

For missing a party, how does "malĉeesti" work?

More seriously, maybe "Vi vivis sen bonega festo!" - "you lived without a great party" could be used until more definitive words come by to assist.

Chainy:You should have come = Vi devintus veni?!

That is how I would usually say it. Although "devus" is quite alright if context makes it clear you're talking about the past, which in this case it does from your previous sentence "you missed a great party".

Chainy:Maybe, 'Vi preterpasis bonegan feston'

I would prefer "maltrafis" to "preterpasis".