Using adjectives as nouns in Spanish

Spanish adjectives can generally serve as nouns as well. 

Generally, the English equivalent is: the/a + adjective + one

Examples: 

• Prefiero la blanca. (I prefer the white one.)
• Ví un gato blanco y uno naranja. (I saw a white cat and a ginger one.)

How to form nouns with adjectives 

To form nouns with adjectives, you need to add an article (definite or indefinite) before the adjective. 

The article must agree in gender and number with the noun it refers to. 

  Example: 

Me gusta la corbata azul, pero prefiero la negra. (I like the blue tie, but I prefer the black one.)

Uses

Adjectives are used as nouns when referring to a noun that was recently mentioned.

Example: 

¿Te gusta la bufanda rosa o la bufanda escocesa? Me gusta la escocesa. (Do you like the pink scarf or the tartan scarf? I like the tartan one.)

To express general or abstract senses, the neuter article lo has to be placed before the adjective. 

  Th English equivalent is: the + adjective + thing or what's where.

  Examples: 

• Lo importante es que estamos juntos. (What's matter/The important thing is that we are together.)
• Lo bonito de esta calle es el castillo. (What's beautiful about this street is the castle.)