Learn Italian: I piatti sono puliti.

i is the plural word for "the" used before masculine nouns that start with most consonants. Since the singular word for plate is il piatto, it becomes i piatti in the plural. The word le is the plural "the" for feminine nouns.

How does the noun piatti form its plural?

In Italian, regular masculine nouns that end in -o in the singular change their ending to -i to become plural. So, the singular piatto (plate) drops the -o and adds an -i to become piatti (plates).

Why does the describing word puliti also end in -i?

Adjectives (describing words) must match the noun they describe in both gender and number. Because i piatti is a masculine plural noun, the adjective pulito (clean) changes its regular singular -o ending to -i to match, becoming puliti.

Wait, doesn't sono mean "I am"?