While that is logical, it crosses the boundaries of how Greek is used. Nominal phrases do not have to agree to the same degree as relative clauses do. Relative clauses are relative clauses and while they have many of the same properties as nominal phrases they are constrained by more rules than nominal phrases - the reason for this is compensation for ambiguity. A noun has a reference, while a pronoun borrows its reference already in the sentence or implied by context - because of which dependency it has to agree more closely in number case and gender than a noun would have to. Without the extra requirements for agreement there is too much ambiguity in meaning and there is a likelihood that understanding would suffer.David Lim wrote:You got the meaning of "indefinite relative pronoun" wrong. It does not mean that it has no reference in the sentence. If you looked at the example of "οστις" that I gave earlier, you can see that "ητις ..." is in apposition to "την ζωην ...", but is called an indefinite relative pronoun. I don't know how the name "indefinite relative pronoun" came about, but if you want my own idiosyncratic explanation of its precise meaning: It creates an indefinite (unspecified) entity X, takes a phrase P of the same type that a relative pronoun takes (where P captures X as the missing part), and returns a noun phrase referring to X. This noun phrase can then be put in apposition to another noun phrase, just as in the example I gave.
The creation of an initially null-value indefinite entity is a theoretical step which doesn't exist in the language and remains an indefinite entity even when it has the returned likeness of a noun phrase (similarly as you can't get rid of i (the unreal number) by assumption). The indefinite entity noun phrase that you have hypothesised has to always draw its existence from the process and the process can only continue to occur in understanding while there is agreement in number, case and gender with an element in the context. A noun has its own existence and can exist when it does not have full agreement with the thing in its context so long as that thing also enjoys its own existence. Nouns seem to be able to be juxtaposed in Greek simply on the basis of case. In the same vein, adjectives in Greek have no independent meaning, so they are required to agree in number, case and gender with their nouns etc.