In Spanish nationalities are expressed through origin adjectives (known as gentilicios in Spanish).
Origin adjectives express where people or things come from.
These adjectives are derived from the name of that place.
There is not a single pattern, as you can see from the following examples.
The adjective for Italia is italiano.
The adjective for Brasil is brasileño.
The adjective for Canadá is canadiense.
The adjective for Francia is francés.
The adjective for España is español.
And there are more patterns.
DIFFERENT FORMS
As adjectives, these words are variable. Some of them have two different forms (singular and plural) and some of them have four forms (masculine-singular, feminine-singular, masculine-plural and feminine-plural).
When the masculine-singular form of the origin adjective ends in -o, there are four forms.
For Italia we have italiano, italiana, italianos and italianas.
You can see how the -o changes in all the examples bellow:
When the masculine-singular form of the origin adjective ends in a consonant, there are four forms.
For España we have español, española, españoles and españolas.
You can see how some letters are added after the consonant in all the examples bellow:
When the masculine-singular form of the origin adjective ends in a vowel other than -o, there are only two forms.
For Canada we have canadiense and canadienses.
You can see how an -s* is added to form the plural in the examples bellow:
*If the masculine-singular form of the adjective ends in an accentuated -í, -es is added to form the plural.
NOUNS & ADJECTIVES AGREEMENT
These adjectives, as any other adjective, must agree with the noun or pronoun in gender and number.
So, if we wanted to say that Antonio is Italian, because Antonio is masculine-singular, we would choose the masculine-singular form of the adjective:
Antonio es italiano.
If we wanted to say that Ana is Italian, because Ana is feminine-singular, we would choose the feminine-singular form of the adjective:
Ana es italiana.
If we wanted to say that Antonio and Mario are Italian, we would choose the masculine-plural form of the adjective:
Antonio y Mario son italianos.
If we wanted to say that Ana and Laura are Italian, we would choose the feminine-plural form of the adjective:
Ana y Laura son italianas.
Remember that, if it's a mixed group of men and women, we use the masculine-plural form of the adjective:
Antonio y Ana son italianos.
In case the adjective has only two forms (singular and plural), such as Canadian, we would do as follows:
Antonio es canadiense.
Laura es canadiense.
Antonio y Mario son canadienses.
Ana y Laura son canadienses.
Antonio y Ana son canadienses.
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