When is it OK to use a subjunctive form instead of the conditional?

Question

My question is a follow-up of this question.

So, with the following sentence, we have querer conjugated in the subjunctive, imperfect past:

Quisiera algo de agua, por favor. | I would like some water, please.

Is this a repeatable pattern, or something that is exclusive to querer? Could I also say the following (using past imperfect subjunctive):

Acabara mis clases en junio. | I would finish my classes in June.

Comiera la comida china. | I would eat Chinese food.

Viviera en Chicago. | I would live in Chicago.

Could I say the following (using simple future subjunctive):

Acabare mis clases el próximo junio. | I'll probably finish my classes in June.

Comiere la comida china más tarde. | I'll probably eat Chinese food later.

Viviere en Chicago el próximo año. | I'll probably live in Chicago next year.

And if the above constructions are valid Spanish, would I sound like a weirdo talking this way?

Answer 1

The construction you're referring to is a courtesy formula. It is a variant of what is called CONDICIONAL DE MODESTIA O DE CORTESÍA in RAE's Nueva Gramática:

23.15ñ El llamado CONDICIONAL DE MODESTIA O DE CORTESÍA es paralelo al imperfecto de ese mismo tipo. De hecho, ambos alternan en esas construcciones -y, a veces, también con el presente-, como en {Desearía ~ Deseaba ~ Deseo} hablar con el doctor. Como en el caso del imperfecto de cortesía (§23.11e* y siguientes), el uso del presente puede resultar demasiado rudo, por lo que se tiende a evitar en fórmulas como No sabría decírtelo con seguridad (Vargas Llosa, Hablador).

^{*Corrected original reference (§25.11e has nothing to do with this topic).}

The variant you're using is a substitution of the simple conditional with the subjunctive tense, explained here:

23.15u (...) la alternancia entre [imperfecto de subjuntivo] y [condicional] se da en el español general, en cambio, con los auxiliares poder, deber y querer en las perífrasis verbales: {Deberías ~ Debieras} prestar más atención; {Podría ~ Pudiera} interpretarse mal, con la excepción, ya analizada, de las prótasis condicionales.
Con el adverbio más y los verbos querer, valer y otros similares se forman expresiones en las que también alternan [condicional] y [imperfecto de subjuntivo], como en ¡Qué más {querría ~ quisiera} yo! o en Más te {valdría ~ valiera} hacer eso.

Now to your question(s):

Is this a repeatable pattern, or something that is exclusive to querer?

As you can see, in most variants of Spanish (there's no such thing as "standard" Spanish, IMO), it would only be valid with certain verbs, like poder, deber, querer, and in certain cases valer, convenir and others of similar meaning.

There are regional dialects of Spanish which do indeed replace the conditional with the past subjunctive in other cases. You can read about them in §23.15d, but those uses are not recommended.

Could I also say the following (using past imperfect subjunctive)?
(...)
Could I say the following (using simple future subjunctive)?
(...)

No, not really. Those uses do not fall within even the dialectal varieties mentioned above, and would probably be wrong in all cases.

Would I sound like a weirdo talking this way?

Definitely :D To many people, even the valid uses of the subjunctive, the imperative or the pluscuamperfect sound pompous and weird, so you might want to stay within the more common tenses, at least when talking with people you don't know well enough.

Answer 2

I read somewhere that this use of the imperfect subjunctive was special to the three verbs: querer/poder/deber. It basically acts as an enhancer to emphasize that there is/was a lot of desire in the case of querer and could've/should've scenarios for the other two.

I'm not a native speaker, but the other examples don't sound good to me. The future subjunctive requires another verb in the examples I can think of that I'm confident in and even if you found one, yes it would usually sound weird if you used it (kind of like old English "thou shalt"). Several times native speaker professors have initially marked me wrong when I've used it assuming I had misspelled another conjugation until I pointed out it was the future subjuntive. They then say it's not used anymore so I have to have examples ready (sea lo que fuere, a donde fueres haz lo que vieres, legal references, the constitution of Spain, etc).

Perhaps a past tense tal vez / quizás / acaso use of the subjunctive could fit what you're looking for as well?

• Tal vez él lo comiera. It's possible he ate it.