Different parts of speech, such as pronouns, adjectives, and conjunctions change forms when used in negative sentences.
If there are any reflexive or direct or indirect object pronouns, they will come between the no and the verb. The only pronoun that precedes the no is the subject pronoun if it's used.
Me compré alguna ropa.
I bought myself some clothes.
No me compré ninguna ropa. or Ninguna ropa me compré.
I don't buy myself any clothes.
You probably noticed that alguno and ninguno can change endings to become feminine and/or plural, as in the case of alguno. These words can be adjectives or pronouns, and the gender of their ending matches the gender of the noun it replaces or modifies.
In the following examples, the words algunas and ninguna are used as adjectives. They precede the noun they modify and must match that noun's gender and number. Keep in mind that negative words have no plural because they indicate that there is none of something, and hence the plural does not apply when there is not even a singular instance to speak of.
Tenemos algunas mascotas.
We have some pets.
No tenemos ninguna mascota. or Ninguna mascota tenemos.
We don't have any pets.
When used as a pronoun, the noun being replaced must already be established so that the correct gender and number can be used.
We have some.
No tenemos ninguna.
We don't have any.
The previous examples use algunas and ninguna as pronouns replacing the understood noun mascotas. Sometimes the pronoun is used with an adjective describing it:
¿Compraste algunas flores?
Did you buy any flowers? ( algunas is an adjective modifying flores)
Compré algunas bonitas.
I bought some pretty ones. ( algunas is a pronoun replacing flores)
I bought some. ( algunas is a pronoun replacing flores)
No compré ninguna flor bonita or Ninguna flor bonita compré.
I didn't buy any pretty flowers. ( ninguna is an adjective modifying flores)
No compré ninguna.
I didn't buy any. ( ninguna is a pronoun replacing flores)
Consider the following examples, and focus on the nouns that the adjectives alguna and ninguna modify and the pronouns that they replace:
Necesito alguna ayuda
I need some help. ( alguna is an adjective modifying ayuda)
Ahorita, necesito alguna.
I need some right now. ( alguna is a pronoun replacing ayuda)
Tú no necesitas ninguna ayuda.
You don't need any help. ( ninguna is an adjective modifying ayuda)
A veces no necesito ninguna pero ahora necesito alguna.
Sometimes I don't need any (I need none), but now I need some. ( alguna and ninguna both are pronouns replacing the word ayuda)
Technically, the words alguno and ninguno are only used as pronouns. If used as an adjective, the –o is dropped, and they change to algún and ningún when followed by a singular masculine noun.
For example, alguno and ninguno drop the –o and are used as adjectives here:
Tú tienes algún dinero. Yo no tengo ningún dinero.
You have some money. I don't have any money.
Now, here is an example of alguno and ninguno being used as pronouns:
Tú tienes dinero y yo quiero alguno. Mi otro amigo no tiene ninguno.
You have lots of money and I want some. My other friend doesn't have any.
Conjunctions: sino and pero
It's important to understand the differences between the conjunctions sino and pero because they can both be translated as “but.”
Sino is used when the first clause of the sentence is negative and the second clause contradicts it. It expresses the concept that in English is stated, “not this but rather that.” Sino is usually translated as “but rather.”
No quiero el coche blanco, sino el coche rojo.
I don't want the white car, but rather the red car.
No nos gusta el cine, sino los deportes.
We don't like movies, but rather sports.
Notice in the following sentences that the conjunction pero is used when the concept is continued rather than contrasted, even if the first sentence is negative.
Yo no quiero ir, pero necesito ir.
I don't want to go, but I need to.
Ellos tienen dinero pero no son felices.
They have money, but they are not happy.
Another use of sino is in the expression “ no solo …sino tambien ….” It is equivalent to the English “not only …but also ….”
No solo tenemos comida, sino también refrescos.
We not only have food, but also beverages.