The interrogative pronouns are used substantively τίς; who? or adjectively τίς ἀνήρ; what man?1263
The interrogatives (pronouns and adverbs, 340, cross346) are used in direct and in indirect questions. In indirect questions
the indefinite relatives ὅστις, etc., are generally used instead of the interrogatives.
τί βούλεται ἡμῖν χρῆσθαι;
τί is used for τίνα as the predicate of a neuter plural subject when the general result is sought and the subject is considered as a unit: ταῦτα δὲ τί ἐστιν;
τίς asks a question concerning the class, τί concerning the nature of a thing:
εἰπὲ τίς ἡ τέχνη
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].