In contrast, when the participle is used as an adjective, it agrees in gender and number with the noun modified.
Similarly, the participle agrees with the subject when it is used with ser to form the "true" (dynamic) passive voice (e.g. La carta fue escrita ayer 'The letter was written [got written] yesterday.
The pronouns yo, tú, vos,[1] él, nosotros, vosotros[2] and ellos are used to symbolise the three persons and two numbers.
Note, however, that Spanish is a pro-drop language, and so it is the norm to omit subject pronouns when not needed for contrast or emphasis.
The first-person plural expressions nosotros, nosotras, tú y yo, or él y yo can be replaced by a noun phrase that includes the speaker (e.g. Los estudiantes tenemos hambre, 'We students are hungry').