In this short grammar lesson, you will learn how to form the plural of words in Spanish. To start, we will introduce you to the main rules.

1. For those nouns ending in the vowels a, e, o and u, the letter "s" is added for the plural form. Therefore the plural of el perro (the dog) is los perros (the dogs). Another example is la casa (the house) which is las casas (the houses) in its plural form.

2. Something different happens for nouns ending in a consonant (b,c,..,s,t,..) including "y" and the vowel "i". In most cases, the letters "es" are added to the end of the word in question. For instance, the plural of el doctor (the doctor) is los doctores (the doctors), la mujer (the woman) is las mujeres (the women) and el rey (the king) is los reyes (the kings).
A further example is the word el autobús (the bus), which already ends in "s" and turns into los autobuses. There are also some exceptions for words ending in "s", indicated below.

Further rules and exceptions:
1. Spanish words ending in "ión" lose the accent in their plural form:
la opción -> las opciones
la civilización -> las civilizaciones

2. For words ending in "z", the "z" turns into a "c":
la luz -> las luces
la vez -> las veces

3. Polysyllabic words ending in "s" or "x" without having the accent on the last syllable, remain unchanged:
el martes -> los martes

4. The accent (both written and spoken) often changes when forming the plural, and has to be adapted according to Spanish accentuation rules:
el ladrón -> los ladrones
el joven -> los jóvenes
el interés -> los intereses