Se vs. si vs. sí vs. sé

Se

  • oneself, himself, herself, itself, yourself, each other, one another (third-person reflexive direct or indirect object pronoun)

    Los policías no saben dónde se escondieron los bandidos. (The police don't know where the criminals hid themselves.)
    No son gemelos, pero se parecen. (You aren't twins, but you look alike.)

  • (used to convey the meaning of the passive voice)

    Se quitó tu nombre de lista. (Your name was removed from the list.)
    Se cree que existen fantasmas en este bosque. (It is believed that ghosts exist in this forest.)

  • (used instead of the indirect object pronouns "le" and "les" before the direct object pronouns "lo", "la", "los", or "las")

    Se lo dimos al hombre. (We gave it to the man.)
    ¿A quién se lo ibas a vender? (Who were you going to sell it to?)

Si

  • if

    Si pierdo el tren, tomaré el bus. (If I miss the train, I'll get on the bus.)
    ¿Y si no les gustan mis regalos? (What if they don't like my presents?)

  • whether, if

    No les importaba si ganaban o no. (They didn't care if they won or not.)
    Pruébate este nuevo traje para ver si te sienta bien. (Try on this new suit to see if it fits well.)

Sí

  • yes

    Sí, estudio varios idiomas. (Yes, I'm studying several languages.)
    Todavía no he dicho que sí. (I haven't said yes yet.)

  • (affirmation not usually explicitly translated)

    Los chicos sí lloran. (Boys do cry.)
    Ellos sí lo saben. (They do know that.)

  • himself, herself, itself, themselves, yourself, yourselves (form of "se" used after prepositions)

    Uno debería dar lo mejor de sí mismo. (One should do one's best.)
    Mi abuela vive por sí sola. (My grandmother lives by herself.)

Sé

  • Presente S/1 (yo) form of the verb SABER (to know)

    Yo sé que ella es bonita. (I know that she is beautiful.)

  • Imperativo afirmativo S/2 (tú) form of the verb SER (to be)

    ¡Sé bueno y apaga la luz! (Be good and turn off the light!)