When to use "eso" or "ese"
I thought that you use "ese" to modify a masculine noun, and "eso" as a demonstrative, but I got corrected. When is each used?
https://www.thoughtco.com/demonstrative-pronouns-spanish-3079351 This website explains about your doubts, specifically eso or ese.
Ese can be used as a demonstrative adjective (Me gusta ese libro. I like that book.) or as a demonstrative pronoun (Me gusta ese. I like that one.)
Eso is only a demonstrative pronoun, and used only when you can't know the gender of something (¿Qué es eso? What is that?) or are referring to a situation or circumstance (Eso es horrible. That is horrible.)
I wrote an answer to a similar question (esta,este, esto) a week ago, so I copy it here:
esta is the feminine version, este is the masculine, and esto is general, neutral. (Same goes for esa, ese, eso)
When you use it in front of a noun:
esta noche - tonight
"Whose cup is this?" ¿De quién es esta taza?
"This church is Catholic." Esta iglesia es católica.
( noche, iglesia and taza are fenimine nouns)
This hat is very feminine." Este sombrero es muy femenino.
When it stands by itself
"I need this" "Necesito esto." Here we dont know what is this, esto is the general word.
"This is my clock." "Este es mi reloj. " Here we already know we are talking about a clock ( el reloj, masculine. So the masuline form is used)
"This is a ball. " Esta es una pelota. Here we already know we are talking about una pelota.
Btw, the plural of este is estos. Which is also the plural of esto. As I see, this distinction disappears in the plural.
"Ese" is masculine, so it is used to modify a masculine noun; you're right.
"Eso" is neuter, meaning that it is used to modify a noun whose gender is unknown or unidentified. For example, if you wanted to say "What is that?", you would say "Qué es eso?" because you don't know what 'it' is.
(Of course, you could also say "What is that thing?", which translates to "Qué es esa cosa?")
Hi! Yes, sounds right. Ese is used together with masculine nouns, and eso is used without any noun following, and when we don't know the gender of the thing we are referring to (or we don't know what the thing is). Are you sure there wasn't some other mistake? Or if it was in one of the newer sections, it may be that you stumbled on a translation that's not yet accepted as correct.