First of all, here are the personal subject pronouns in Spanish:
- yo — I
- tú — you (singular familiar)
- usted — you (singular formal)
- él, ella — he, she
- nosotros, nosotras — we
- vosotros, vosotras — you (plural familiar)
- ustedes — you (plural formal)
- ellos, ellas — they
Because the verb form often indicates who the subject of a sentence is, one can properly leave out the subject pronoun or put it at various places in the sentence. Voy a la escuela, yo voy a la escuela, voy yo a la escuela, and voy a la escuela yo are all grammatically correct ways of saying "I am going to the school" (although the final option would be uncommon except if said for poetic effect). But the placement of the pronoun can make a difference in how the sentence is understood.
To see how these pronouns are used, examine the sentences below. Pronouns, where used, are in boldface:
- Mi hermano es muy inteligente. Es doctor. (My brother is intelligent. He's a doctor.) — No subject pronoun is needed in the second sentence, because the subject of the sentence is made clear by the context and the verb form. Generally, and especially in writing, unneeded pronouns aren't included unless there's a reason for doing so.
- Es fácil comprender el libro. (It is easy to understand the book.) — No pronoun is used to translate an impersonal use of "it."
- Mi hermano y su esposa son inteligentes. Él es doctor, y ella es abogado. (My brother and his wife are intelligent. He is a doctor, and she is a lawyer.) — In this case, the subject pronouns él and ella are needed for clarity.
- Tú, ella y yo vamos al cine. (You, she and I are going to the movies.) — Note that in this construction the first-person plural form of the verb is used. Thus it is possible to use that verb form without using the pronoun nosotros.
- Hazlo. (Do it.) Hazlo tú. (You do it.) — In a command such as this, the addition of the subject often has a similar effect to its use in English. Although grammatically not necessary, the addition of the subject serves to place additional emphasis on the subject.
- Ella canta bien. (She sings well.) Canta bien ella. She sings well. — By placing ella at the end of the sentence, the speaker is placing a strong emphasis on the pronoun. The emphasis in the second sentence is on the singer and not the singing.
- ¿Vas a salir? (Are you leaving?) ¿Vas a salir tú? (Are you leaving?) — The first sentence is a simple, uninflected question. But the second one, by adding the subject at the end of sentence, is placing a strong emphasis on the person leaving. One possible translation might be "Are even you leaving?"
- Nunca va ella al centro. (She never goes downtown.) Ya ha salido él. (He has already left.) — It is common when certain adverbs start a sentence to immediately follow the adverb with the verb, followed by the subject. No special emphasis on the subject is intended. Adverbs often used this way include nunca, ya, bastante, and quizás.
- — Te amo, dijo él. — También te amo, respondió ella. ("I love you," he said. "I love you too," she responded.) — When reporting what people have said, it is common to use the subject pronoun after verbs such as decir (to say), preguntar (to ask), and responder (to reply). No special emphasis on the speaker is intended.