In Spanish grammar, the term ‘indefinidos’ refers to a grammatical category of words that express an undetermined or non-existent quantity.

Indefinidos can range from adjectives, adverbs and pronouns which give the nouns they modify or replace an undetermined value.

AFIRMATIVO                     NEGATIVO

algo                                      nada

alguien                                 nadie

     alguno                                  ninguno

 

We use algo, alguien y alguno in affirmative phrases and nada, nadie y ninguno in negative ones.

Algo is a neutral indefinido pronoun that we use to indicate an undetermined object or action:

• ¿Hiciste algo interesante durante las vacaciones de verano? Did you do anything interesting during the summer vacations?

Algo can also be a synonym of  un poco.

• El español es algo parecido al portugués. Spanish is somewhat similar to Portuguese.
• Yo hablo algo de francés. I speak a little bit of French.

 

Nada is a neutral indefinido pronoun that serves as opposite for algo and todo.

• ¿Haces algo este sábado? No, no hago nada. Are you doing anything this Saturday? No, I have nothing planned.

Nada can also act as a synonym for en absoluto (not at all), ni un poquito (not a bit).

• No me gusta nada mi jefe. I don’t like my boss at all.
• Yo no hablo nada de alemán. I don’t speak German at all.

 

Alguien is a noun that’s always masculine and it does not have a plural form. We always use it to describe an undetermined person; we do not use to refer to objects or animals.

• ¿Vieron ustedes a alguien conocido en la fiesta de Rocío? Did you see anyone you know at Rocío’s party?

 

Nadie is an invariable noun that’s paired with singular verb forms. Nadie refers to a non-existent person only; we do not use to refer to objects or animals.

• No había nadie en la oficina ayer. There was no one at the office yesterday.

 

Alguno (a, os, as) can be a pronoun or an adjective and it can refer to one or more undetermined persons or objects. We use it to indicate to one or more persons or objects within a group.

When we use alguno as a singular masculine adjective, we switch to it’s abbreviated form: algún.

When we use the plural form of alguno/alguna, we are describing an undetermined quantity that’s not overly abundant.

• ¿Tienes algún amigo mexicano? Do you have any Mexican friends?
• Sí, tengo algunos. Yes, I have a few.

 

Ninguno is a negative pronoun or adjective that serves as opposite for todo or alguno.

When we use ninguno as a singular masculine adjective, we switch to it’s abbreviated form: ningún.

• ¿Todas tus amigas van a ir a protestar?  No, no va ninguna. Are all your friends going to the protest? No, none of them going.
• ¿Tienes algún problema con la gramática? No, no tengo ningún problema. Do you have any problems with grammar? No, I have no problems with it.

 

Careful! When nada, nadie or ninguno are placed before the verb, they replace ‘no’ as the verb negative indicator.

• Nada les interesa a los jóvenes. Nothing sparks interest in young people.
• Nadie lo quiere por ser tan detestable. No one likes him because he’s so obnoxious.
• Ningún miembro de su familia lo visita porque es un cascarrabias. No one in his family visits him because he’s a grump.

However, if these words are placed after the verb, we do use ‘no’ forming a double negative for emphasis:

• A Juan no le interesa nada la política. Juan is not interested in politics at all.
• No lo visita ningún miembro de su familia. He is not visited by anyone in his family.