Indefinite subject

  1. In Russian we express the indefinite subject with the third person plural of the verb, but without the third person pronoun:
    Indefinite: Говорят, что он интересный человек.
    Definite: Они говорят, что он интересный человек.
  2. In the second example, since we use the pronoun они, the subject is definite because we have specific individuals in mind.
  3. The particles -то and -нибудь are added to interrogative pronouns (question words) to form indefinite pronouns:
    кто-то, кто-нибудь
    что-то, что-нибудь
    где-то, где-нибудь
    как-то, как-нибудь
    почему-то, почему-нибудь
    какой-то, какой-нибудь
    чей-то, чей-нибудь
  4. For English speakers it's sometimes difficult to figure out which particle to use in a given situation.
  5. As a general rule, the particle -то is used when the exact identity of the person, place, etc. is only partially known to the speaker, or when the speaker knows the identity but does not reveal it to the listener:
    Кто-то мне зказал, что вы хороший студент.
    Someone told me that you are a good student.
  6. In the previous example, the speaker may know the identity of someone, but does not feel it is necessary to reveal it to the listener. It is also possible that the speaker does not remember who this someone was; the speaker may not know someone's name, for example.
  7. The particle -нибудь is used when the speaker does not know anything about the identity of the person, place, etc. It could be anyone, anything, anyplace.
  8. The particle -нибудь is often used in questions and commands:
    Кто-нибудь мне звонил вчера? Did anyone (at all) call me yesterday?
    Купи мне что-нибудь в магазине. Buy me something (anything at all) at the store.
  9. We use the indefinite particle -нибудь in questions because we don't know anything about the answer. The answer could be anything.
  10. In the second sentence (command), we use the particle -нибудь because we ask the person to buy anything at all. We don't know anything about the object that will be bought. It could be anything.
  11. The indefinite pronouns and adjectives кто-, что-, чей- and какой- will take appropriate case endings, but the indefinite particles -то and -нибудь will remain the same: Вы кому-нибудь говорили об этом?
    Вчера она нам о чём-то рассказывала.