Are clauses such as "¡Que le vaya bien!" in Spanish subordinate?

Question

As far as I know, basically by definition, subordinate clauses must be embedded in a matrix clause. Therefore, if sentences of the type "¡Que le vaya bien!" are subordinate, where is the matrix clause? Some have said that such constructions result from the omission of a main verb such as espero (i.e., "¡Espero que le vaya bien!"). Would Spanish speakers interpret the two sentences as equivalent then?

On the other hand, if they are not subordinate, what is the function of the subordinator "que"? How should its presence be analyzed?

I've looked for similar examples of subordinate clauses being used as complete sentences. The only one that came to mind is "If only . . . !" in English, but the Cambridge Grammar of the English Language says that in this case, it's just that "the apodosis is omitted."

It also occurred to me that the "que + subjunctive verb" construction is similar to "would that . . ." in English, but I think it's clear with "would that . . ." that there is indeed a main verb with an omitted subject "I."

Answer 1

I haven't found a specific grammatical term or label for this usage, but all online resources that deal with the Spanish subjunctive explain it in the same terms as proposed in the question, i. e. that there's a verb expressing hope or expectation implied as the main clause (it could be esperar or desear).

Pairs like ¡Que le vaya bien! and Espero que le vaya bien are semantically almost identical, but the intonation is rather different and a native speaker would not perceive the two sentences as socially equivalent. There's a reason why the former kind (beginning with que) is almost always written with an admiration point: it works rather as an interjection. It sounds emotional and spontaneous and it would also be the correct choice to insert an ironic tone. On the other hand the latter type of sentence (with the verb esperar) is a complete sentence with normal prosody (not an exclamation, generally), and it states or reports a fact: that the speaker hopes for something. You would use the former as you wave someone goodbye before a journey, as they board the plane; the latter would be used if you had a while to sit down with someone.

In any case the difference is subtle. There's a third choice, too, which somehow bridges that gap: using ojalá to head the subjunctive clause. It works as a hoping/wishing verb; indeed it comes from Arabic لو شاء الله law šá lláh, meaning "if God wanted" ~ "may God want".