Indefinite nominal pronouns, such as someone or something, fall into the following types:

IP=Q: Indefinite pronouns are identical to interrogative pronouns.

IPQ: The stem of indefinite pronouns is identical to that of interrogative pronouns.

IP~Q: Indefiniteness is expressed by a special bound morpheme that usually – but not necessarily – has an etymological relationship to words meaning ‘be,’ ‘want,’ ‘maybe,’ ‘or,’ and ‘too.’

IP~N: Independent indefinite pronouns are formed from generic nouns meaning ‘person’ or ‘thing.’ The number ‘one’ may be used instead of ‘person,’ often with a morpheme expressing indefiniteness.[1]

IP=IP: These specific indefinite pronouns contain a root not related (synchronically) to the roots of any other words in the language.

IP=Clause: Existential structures function as independent pronouns (not present as a separate word class in the language) and are considered dependent clauses even in synchrony (such as ‘there is someone who...’ and ‘there is something that...’).

+Free: This value is added to another value if free-choice (non-nominal) indefinite pronouns (any-) differ in type from that of nominal pronouns.[2]

[1] Although it is often difficult to distinguish an indefinite pronoun from a common attribute + noun, an independent indefinite pronoun can be identified when its behavior is not fully explained by the rules governing its individual components.

[2] This value requires attaching the value of the non-nominal pronoun to Free; for example, IP~N+FreeIP~Q indicates that the nominal indefinite pronoun is type IP~N, while the non-nominal is type IP~Q.