Spanish 'This' and 'That' (este, ese, aquel)

• este / esta / esto (and their plurals): Refer to items or concepts close to the speaker. Think of something you can easily touch or hold, or an idea just expressed by you. For instance, if you are holding a pen, you would say Necesito este (I need this one) if you need that specific pen.

• ese / esa / eso (and their plurals): Refer to items or concepts at a medium distance, typically close to the listener or slightly removed from the speaker and listener. This implies a moderate separation. If a book is on the table next to your friend, you might ask ¿Me pasas ese? (Can you pass me that one?).

• aquel / aquella / aquello (and their plurals): Refer to items or concepts far away from both the speaker and the listener. This distance can be physical (e.g., across the street) or temporal (e.g., a long time ago). Pointing to a distant building, you could remark Aquella es muy antigua. (That one over there is very old).

You should use neutral forms when you are referring to:

• An abstract idea, concept, or situation, rather than a specific noun with a gender. For example, Eso es imposible. (That [idea/situation] is impossible.)
• An unknown object or item whose gender you do not know or do not wish to specify. For instance, if someone hands you something unfamiliar, you might ask, ¿Qué es esto? (What is this thing?)
• An entire sentence or clause that has just been said or written. Él dijo que no vendría; eso me sorprendió. (He said he wouldn't come; that surprised me.)

Generally, no. Using neutral forms like esto or eso to refer to a person is considered impersonal and can be disrespectful or dehumanizing, as it treats the person as an object or an unknown 'thing.' Always use the appropriate masculine/feminine demonstrative pronoun (este, esta, ese, esa, aquel, aquella) if referring to a specific person, or better yet, use personal pronouns (él, ella, usted) or their name. For example, instead of ¿Quién es eso?, say ¿Quién es esa persona? or ¿Quién es él?.

The difference lies in the degree of distance from both the speaker and the listener.

• Ese implies something at a medium distance, often visible and within the general vicinity, perhaps closer to the listener than to the speaker. Think of an item across a small room or on a nearby shelf. Dame ese libro. (Give me that book [on the table next to you]).
• Aquel implies something farther away, often out of easy reach, perhaps across a larger space, or even out of sight in a different location or time. Think of a distant building or a memory from long ago. ¿Recuerdas aquel viaje a Madrid? (Do you remember that [distant] trip to Madrid?). While ese is broadly used, aquel maintains a clear sense of greater remoteness.

The Real Academia Española (RAE) no longer requires accent marks on demonstrative pronouns (éste, ése, aquél) in most cases since 2010. The meaning is almost always clear from context without them. You will find them in older texts, but for modern communication and general learning, you can safely omit them. Only in very rare, truly ambiguous sentences where the demonstrative pronoun could be confused with its adjective counterpart might an accent be considered, but this situation is highly uncommon and usually easily resolved by rephrasing.

You rely heavily on context. In a real conversation, the noun being replaced is usually clear from what was just said or from the visual situation. For example, if someone asks ¿Te gusta la falda? (Do you like the skirt?), and you respond Sí, me gusta esa. (Yes, I like that one.), the esa clearly refers to la falda (feminine singular). If the context doesn't make the gender clear, or if you're referring to an abstract idea, then the neutral forms (esto, eso, aquello) are appropriate.