There are two types of demonstratives: demonstrative adjectives and demonstrative pronouns.
A demonstrative adjective is a word used to describe a noun.
A demonstrative pronoun is the word which takes the place of a noun.
First, demonstrative adjectives. There are various forms, depending on the gender of the noun /object (masculine or feminine), whether it’s singular or plural, and whether the noun is perceived as being close to us or not.
aquel (that one over there)
In total there are 12 forms of demonstrative adjectives, divided into 3 groups according to their perceived distance from us:
este libro (this book)
estos libros (these books)
esta pluma (this pen)
estas plumas (these pens)
ese libro (that book)
esos libros (those books)
esa pluma (that pen)
esas plumas (those pens)
aquel libro (that book over there)
aquellos libros (those books over there)
aquella pluma (that pen over there)
aquellas plumas (those pens over there)
Here are the corresponding demonstrative pronouns:
este (this one – masculine)
estos (these ones – masculine)
esta (this one – feminine)
estas (these ones – feminine)
ese (that one – masculine)
esos (those ones – masculine)
esa (that one – feminine)
esas (those ones – feminine)
aquel (that one over there – masc.)
aquellos (those ones over there – masc.)
aquella (that one over there – fem.)
aquellas (those ones over there – fem.)
Each demonstrative pronoun also has a neuter form. They do not change according to number or gender, and they are used to refer to abstract ideas, or to an unknown object:
esto (this matter, this thing)
eso (that matter, that thing)
aquello (that matter/thing over there)
*In the past the demonstrative pronouns always carried a written accent, while the demonstrative adjectives did not.