Learn Portuguese (Portugal): As casas são pequenas.

In Portuguese, the word for "the" must match the gender and number of the noun it goes with. Because casa (house) is a feminine word, its plural form casas needs the feminine plural article as. If it were a masculine plural noun, like carros (cars), you would use os.

Why is the verb são used here to mean "are"?

São is the plural form of the verb ser used for "they are" (in this case, referring to the houses). We use the verb ser because the size of a building is considered a permanent or defining characteristic, not a temporary state.

Why does the word for small, pequenas, have an -s at the end?

In English, adjectives never change (we say "small house" and "small houses"). But in Portuguese, adjectives have to match the noun they describe in both gender (masculine or feminine) and number (singular or plural). Since casas is feminine and plural, the adjective becomes pequenas.

If I wanted to drop "The houses" and just say "They are small," which Portuguese pronoun would I use?