Neutral demonstratives are always pronouns and serve to designate abstract ideas, something whose name has or has not been mentioned, or unknown nouns.
Eso es cierto pero no son asuntos nuestros.
That is true, but it is not our business.
Quick Review of Demonstratives
Rule 1. Demonstratives are used to identify a person, animal, or thing by indicating its distance from the speaker. They can be determiners or pronouns.
¿Esos libros son tuyos?
Are those books yours?
They can also be used with time.
Ese día fue grandioso.
That day was great.
Neutral Demonstratives in Phrases
Rule 2. Neutral demonstratives (esto, eso, and aquello) on the other hand, are always pronouns and are used to talk about abstract ideas or nouns, things that have been previously mentioned, and unknown subjects.
These demonstratives are frequently used with the verb ser, as shown in the following construction:
eso, aquello, esto + verb ser
Aquello fue su ruina.
That was his undoing.
The verb ser can be conjugated in any tense.
How to Use This Construction?
Rule 3. Demonstratives, regardless if they are determiners or pronouns and whether they are used to talk about length or time, always maintain the same essence of distance.
That is, esto expresses closeness to the speaker or the idea, eso a medium closeness, and aquello a greater distance. The same applies when using these constructions to refer to abstract ideas.
To understand this better, we will give you some examples, so you can see these pronouns used in context.
- Example 1: This is a conversation between two friends that are beginning a trip and are talking about precautions to take.
Esto será lo que tendrás que hacer si te enfermas.
This is what you will have to do if you get sick.
Here, we can understand that one of the friends is referring to some cure, some type of instructions, etc.
The speaker is using esto, because the instructions are 'close' to them in a form, probably because they have been mentioned or because the friend is about to say it. They are talking about preventing something that may happen, so the verb ser is conjugated in the futuro simple.
- Example 2: This is a group discussion where different people are sharing their points of view.
Eso es un muy buen punto, ¿tú qué piensas?
That's a very good point, what do you think?
In this case, the speaker used eso, probably because the opinion was given by someone else, which creates some distance. Since this is a discussion that is happening in the present, the verb ser is conjugated accordingly.
- Example 3: Finally, these are two friends that are talking about memories they have shared together.
Aquello fue todo un espectáculo.
That was quite a show.
In this case, the speaker used aquello, because it is probably a distant memory of an event that has already been mentioned. In this case, since the context is in the past, the verb ser is conjugated in pretérito.
___ una gran idea, ¡hagámoslo!
(An idea given by another person in a conversation)