Do "direct object を" and "directional を" occupy the same slot?

Question

*A Dictionary of Basic Japanese Grammar* (ADoBJG) lists more than one を particle. In particular: - On page 347, it lists **o**¹, *a particle which marks a direct object*. - On page 349, it lists **o**², *a particle which indicates a space in / on / across / through / along which s.o. or s.t. moves*. The second particle, which I'll call <i>directional を</i>, appears to be used quite differently from the <i>direct object を</i>. According to ADoBJG, the directional を is used only with verbs of motion, which I think are generally intransitive. For example, directional を appears in the phrase `空を飛ぶ`, combining the intransitive verb of motion `飛ぶ` with an を-marked noun. Since it's listed as a separate particle in ADoBJG, and since it behaves so differently, and since it appears in different contexts from the other を, I've always thought of directional を as a *separate particle* which happens to be *written and pronounced the same way*. However, in 国語辞典s such as [大辞林 and 大辞泉](http://kotobank.jp/word/%E3%82%92), both usages are listed under the same entry. So I'm wondering how independent the two really are. It seems to me that, because directional を appears with intransitive verbs, and because direct object を appears with transitive verbs, the two occupy separate syntactic slots. That makes me wonder if it's possible to take a construction such as 空を飛ぶ, which uses the directional を, and turn it into a transitive construction which *also* takes the direct object を, such as `◯◯を空を飛ばす`. My thought is this: if they don't really occupy different slots, then this is ungrammatical because of the *double-o constraint*, which says that a single verb phrase may have no more than one を-marked noun phrase. But if they *do* occupy different slots, and they're really different particles, then you should be able to create a single verb phrase containing both. I'm not sure my `◯◯を空を飛ばす` example is very good. (It's supposed to mean *"send ◯◯ flying through the air"*.) But if it's possible to create a grammatical example combining both directional を and direct object を, I would like to know, regardless of whether my particular example is very good. **Is it possible to create such a construction?**

Answer 1

を is a direct object marker and is usually placed after the most important noun or the word that you are emphasizing the most. To use it twice would indicate two initial subjects in your sentence and thus not make much sense. As for directional and direct object, having one or the other translates the sentence differently and requires another particle to fill in the other space. So ”OOをそらに飛ぶ” or "OOは空を飛ぶ” would be a better translation as to not confuse which subject you are talking about. There really isn't much of a difference between directional and direct object. They are really only an issue when you try to translate it to English. It is probably mentioned twice in the book to point out the different circumstances in which it can be used.