I ate at a Mexican restaurant tonight and they had a sign posted “Benvenidos: mi casa es su casa” I don’t know any Spanish, but the phrase clearly means: “my house is your house”. But I began to wonder about the word “su”. I guess the easiest way to pose my question is to ask whether the accurate French translation is “ma maison est ta maison” or “ma maison est votre maison”. Or am I missing something?
Isn’t this analogous to addressing a single German person as ‘Sie’? It’s just formality/politeness.
ETA so, votre
In this case, the second.
Su is the possessive for the third person (singular object, any genders; for multiple objects, sus). In Spanish, respectful forms of the second person behave grammatically as if they were third persons. If you and I were talking about, say, Dave’s recipe or Hannah’s recipe, or one recipe they developed between the two of them, it would be su receta as well; if more than one recipe, sus recetas.
More familiarly, you could say “Mi casa es tu casa,” which is equivalent to the first form in French. Both are used.
I see advertising slogans using both informal (tu) and formal (su) forms in addressing the public. My impression is that the former is more common.
As I understand it, the formal is third person “usted” rather than “tu” - developed along the same lines as the old English “My lord”
“Yes, my lord.”
“Does my lord want his meal prepared?” when addressing a more important person, is more formal/respectful than “You want your meal prepared?” Notice then all references formally to a 2nd person are actually in 3rd person.
So “Usted quiera su comida?” (Hey, it’s been 40 years since I studied Spanish…) compared with “Tu quieras tu comida?”
I’m sure a real Spanglophone can correct this…?
Right. More specifically, it was originally “does your mercy want his meal prepared?”
“vuestra merced” evolved into “usted.”
I can try: *su *and *suyo *are formal and respectful, like the use of the third person you mentioned. *Tu *and *tuyo *are informal. There is no equivalence in English, but there is in French (*ta maison *and votre maison, in the example of the house), in German (*Dein *and Ihr), and many other languages.
In proper Spanish your questions would read: ¿Desea usted su comida? and ¿quieres la comida? (the *tú *being implicit by the verb conjugation, it does not need to be said and mostly is not. I think the posh term to denote this laziness of speech is parsimony).
Just in case you wondered: *tu *means yours, *tú *means you: the accent, usually not used in monosylabic words, is necessary to make this difference. In the questions it is not necesary to state that the food is yours as you are getting it served, it is obvious and thus implicit. No *tu *needed. You can say *su *though in the more respectful setting, it reiterates the deference.
Thanks. This has been interesting. So it is a bit like German using the 3rd person for the respectful form. That is what I didn’t understand and why I raised the question.
Thanks. I’ve learned my one thing for the day now, I can go home… 
That was very informative! I like learning things like that.
I’m going back to bed.
Likewise in Portuguese the formal “you” is third-person: o senhor/a senhora = sir/madam.
Just don’t try it in latin: domus mea domus tua esto.
“Romanus eunt domum”?
I mean that in classical Latin, unlike French, Spanish, etc., AFAIK you should always address one person as ‘tu’, and more than one person as ‘vos’.