title_body: Usage of different plural systems in the same language
upvoted_answer: A similar system to the one you describe is attested in Fijian. Fijian has a single-dual-paucal-plural distinction in its pronouns only. However, almost every sentence must contain a subject pronoun. I'm not sure about the status of imperatives in Fijian. Fijian also has VOS word order, where S is a lexical subject.
  
  Independent nouns themselves are not marked for number and the articles that introduce them are also not marked for number.
  
  era la'o [a gone]
  3PL go   DET child
  The children are going
  
  
  In other examples, a gone is glossed as the child. From this we can infer that the subject pronoun (or part of the verb phrase, depending on how you analyze it), is usually the only place in the clause where number is overtly marked. Pronouns can surface in other positions as well, and pronominal number contrasts are not neutralized when the pronoun isn't the subject.
  
  As an interesting wrinkle, pronouns have a separate form that's used when they are the head of a noun phrase, including a subject noun phrase.
  
  era sa  la'o [o   ira]
  3PL ASP go   ART  3PL
  "They are going"
  
  
  But, pronouns can occur after the verb without being introduced by an article or a preposition if they are objects.
  
    o   aa   biu-ti  ira
  2SG PAST leave-TR  3PL
  "You left them"
  
  
  More generally, it is somewhat common for pronouns or a subset of the pronouns to have a different number system than independent nouns. Proto-Germanic is reconstructed with dual number in first and second person pronouns and their corresponding verbal forms, but without the dual in the third person or in nouns.