Why is it "que pases una buena tarde" but "que

why is it “que pases una buena tarde” but “que pases unas buenas noches” - why una-unas buena-buenas if both nouns are singular f?

Noches is not singular, it is the plural of noche.

I think is a mistake.
Often it says two expressions:
buenas tardes (this is plural ) or que pases una buena tarde(this is singular a refer only this afternoon)
buenas noches (plural) or que pases una buena noche(singular)
for example you find someone ,you say buenas tardes. When you go ,you can say buenas tardes or que tengas una buena tarde.
mfr is right.

if noches is not singular, then how can you use “una” or “unas” in this case. If “una” means one, how can there be a plural of “una”?

@AnitainUS- “Unas” and “unos” translate as “some”.

Un taco…unos tacos.
Una fiesta…unas fiestas

@danifernadez- The recording, made by LingQ members Berta and Albert from Spain, definitely says “Unas noches.” This was new for me.

When I use que pases una buena noche ,I use singular word It is like the people speaks in my region . I live in Andalucía in south of Spain. I don´t know in them region how they say, but in Andalucia use singular form .

it is a vernacular expression. You are wishing the person a good future, not just a good night.

I’ve asked a translator friend an he tells me:

Actually both sentences are correct, you can either say “que pases unas buenas noches” or “que pases una buena noche”.

Here is the thing, when you use the singular form it is usually used if you’re going to a party or a date or you’re ill, then you say “que pases una buena noche”. Because something very special is happening that night (a date or a party… or you’re ill and you may have a difficult night because of your illness). You want that person to have luck on her/his date, or luck with the symptoms of her/his illness during that nigh… etc

But it is also correct to say in that situation “que pases unas buenas noches”, only that you’re being more specific if you use the singular form there. But either way is correct.

Aside from this, my friend says you should better use “que TENGAS” instead of “que PASES”. It’s not incorrect to use “pases”, in fact most people use this, but formally he says it’s best (prettier) if you say “tengas”.

Berta
IDEL
Spanish lessons at Lingq