Why does "devus" translate as "should?"

Question

In Esperanto, we write devus whenever we translate "should," but it literally translates as would have to. Why is this, and are there any alternatives to devus?

Answer 1

This is explained well in PMEG:

La verba finaĵo US normale montras, ke temas pri nereala, imagata ago. Sed la verbaj formoj povus, devus kaj volus havas tamen specialan signifon. Plej ofte ili esprimas realan devon, povon aŭ volon rilate al ago, kiun oni tamen ne faris, faras aŭ faros:

• Mi devus labori. = Ja ekzistas por mi devo labori, sed mi tamen ne laboras.
• Mi povus foriri. = Eblas al mi foriri, sed mi tamen restos.
• Mi volus helpi al vi. = Mi ja volas helpi al vi, sed tio ne eblas.
• Ili iris, sed ĝuste en la direkto ĝuste kontraŭa al tiu, en kiu ili devus iri. FA3.89
• Mi povus ĵuri al vi, ke ili estas sinceraj. Rt.73 Verŝajne mi tamen ne ĵuros, ĉar ne necesas.
• Volus kato fiŝojn, sed la akvon ĝi timas. PE.2616

Iafoje povus, devus kaj volus tamen povas aperi kun la ordinara nerealeca senco de la US-finaĵo:

• En grupo respektege staris en angulo la pastraro de la ĉirkaŭaĵo, kvazaŭ devus okazi enterigo, sed tie estis gaja festo, ĝi nur ankoraŭ ne sufiĉe ekmoviĝis. FA3.49 La devo estis nur ŝajno.

English translation:

The verb ending US normally indicates that the action is unreal or imagined. But the verb forms povus, devus and volus have a special meaning. Most often they express a real ability, obligation or desire related to an action that one, however, did not do, is not doing or will not do:

• Mi devus labori. (I should work.) = I do have the obligation to work, but nevertheless I'm not working.
• Mi povus foriri. (I could leave.) = It is possible for me for leave, but nevertheless I'm staying.
• Mi volus helpi al vi. (I would like to help you.) = I do actually want to help you, but that's not possible.
• Ili iris, sed ĝuste en la direkto ĝuste kontraŭa al tiu, en kiu ili devus iri. FA3.89 (They went, but precisely in the direction opposite to the one in which they should go.)
• Mi povus ĵuri al vi, ke ili estas sinceraj. Rt.73 (I could swear an oath to you that they are sincere.) Probably I will not actually swear an oath, as it is not necessary.
• Volus kato fiŝojn, sed la akvon ĝi timas. PE.2616 (A cat would like to have fish, but it fears the water.)

But sometimes povus, devus and volus are used with the ordinary irreal meaning of the US-ending:

• En grupo respektege staris en angulo la pastraro de la ĉirkaŭaĵo, kvazaŭ devus okazi enterigo, sed tie estis gaja festo, ĝi nur ankoraŭ ne sufiĉe ekmoviĝis. FA3.49 (The pastors from the vicinity stood very respectfully in a group, as if a burial had to happen, but actually a cheerful celebration was taking place, it just hadn't started moving yet.) There only seemed to be an obligation.

Answer 2

The answer to "Why?" is that Esperanto is in some respects a pseudo-Romance language, and this is more or less how the others do it. Speakers of those languages find it entirely natural to use the conditional in this way.

In French, "I should go" and "I should have gone" are rendered as je devrais partir; j'aurais dû aller. In Italian: dovrei andare; sarei dovuto andare. Similar constructions are used in Spanish, Portuguese and Romanian. ("I would have had to" must be rendered as J'aurais été obligé de... which in Esperanto becomes Mi estintus devigata...)

So devus, devintus ("should have"), and devontus ("ought to [later]") provide the standard and easy solution, but are somewhat problematic because of the ambiguity. You can avoid devus by using laŭdeve ...-us, or similar constructions with laŭ, or Pli bonus, se....

Laŭdeve mi lavus la fenestrojn, sed mi estas tro laca.

Pli bonus se vi remetus ĝin en la ŝrankon.

Pli decus se ni aĉetus la alian.

Here's an example of a real difficulty. Consider the sentence

You should move the first pawn, as otherwise you'd have to move the second.

It appears as though you have to write

Vi devus movi la unuan peonon, ĉar alie vi devus movi la duan.

But that seems to imply that moving the second pawn is your second-best option, when in fact it is what you're trying to avoid. We can rewrite the sentence to avoid devus:

Laŭprudente vi movus la unuan peonon, ĉar alie vi devigatus movi la duan.

Laŭ prudento vi movus la unuan peonon, ĉar alie vi estus devigata movi la duan.

Answer 3

Modality (which is the technical term for the aspect of language that deals with expressing obligation, probability, etc) is very nuanced, so it's a tricky feature to translate. Different languages have different ways of expressing it. There are also degrees of intensity in the various expressions.

Dev/i does express obligation (have to, must), but the form devus signifies conditionality. This can be expressed as You would have to do this if you want to achieve X, but IMHO this is equivalent to You should do this if you want to achieve X. In Eo these would both be Vi devus fari tion se vi volas atingi X.

As I said, it's a complex topic, and I cannot easily explain this in a few paragraphs. I would simply say that should is an appropriate translation for devus; bearing in mind that translation is never a one-to-one match between languages!

Answer 4

As far as I can tell, some people think that "Should" means the same thing as "Would have to" (Devus), and others think that it means the same as "Have to" (Devas).

Basically whoever set the rules when this was decided were in the first group and now we're stuck with it.