Last night I was inputting the first and second chapters from Baghy's La Verda Koro into the computer and the question arose: just what is the difference between kiu and kia? More precisely, why does Esperanto have two adjective forms among the correlatives?
Simple answer: it doesn't. Kiu isn't an adjective, even though you can ask:
Kiu libro estas sur la tablo? = Which book is on the table?
Kiu and its corresponding forms (tiu, ĉiu, neniu, iu) is one of a small class of words that serve not as modifiers (they add nothing to the description of the object to which they are attached) but as selectors (they choose one or more objects out from among a group of similar, or even identical, objects). The only other word I can think of in this group (maybe you can come up with another!) is the definite article la. (1)
For reasons that probably seemed good to them at the time, western grammarians decided to include these words under the general rubric of "adjectives" (possibly because, in Latin, their equivalents used the formal adjective endings). But, really, in Esperanto they are a different kind of word entirely. (Frankly, in English they're a different kind of word entirely -- but I don't want to get into a shouting match with generations of experts...)
Kia, on the other hand, really does refer to the description of a particular object:
Kia libro estas sur la tablo? = What sort of book is on the table?
"What sort of" in English obviously isn't an adjective -- it's not even a single word. But it does ask for some sort of description of the object with which it is associated.
Which one of kiu, kia should you use in any particular case? The above information should be enough to tell you, but there's another very easy criterion to use:
(1) If the answer to your question requires a name, or a word like la or tiu, in it, use kiu (it is a selection question). Answers to kiu should always include one of these as a primary component.
(2) If the answer to your question requires an adjective, or something that can serve as an adjective (like a prepositional phrase), use kia (it is a description question). Answers to kia should never include a name or a word like la or tiu as a primary component.
(Note that (1) can include adjectives in the answer, but only when they are used to select, not modify: "Kiu libro estas sur la tablo? La flava libro estas sur la tablo" (as distinct from the red book, or the moldy book; note use of "la"). (2) can include a name, or la or tiu, but only when this is part of some sort of phrase serving as an adjective: "Kia libro estas sur la tablo? Flava libro estas sur la tablo. Libro kiel tiu de Georgo estas sur la tablo." (Note inclusion of "tiu" only within a subordinate expression, not as a primary component.))
Simple exercises:
(1) Answer the two questions given above: "Kiu libro estas sur la tablo?" and "Kia libro estas sur la tablo?"
(2) Answer the two questions: "Kiu vi estas?" and "Kia vi estas?"
Don Harlow <donh@donh.best.vwh.net>