The grammar of 教授がハリーをひとり占めにはできなかった


> みんなが寄ってくるので、 **教授がハリーをひとり占めにはできなかった** 。  
>  Everyone had gathered round, so the professor was unable to monopolise
> Harry.

I'm struggling with the grammar of the second clause here. The closest
structure I can see is XをYにする i.e. make X into Y, but in potential form.
Literally "the professor was unable to make Harry a monopolisation". I also
wonder why は is needed.

ひとり占め apparently works as a する verb, so why not simply 教授がハリーをひとり占めできなかった? In
fact why not 教授 **は** ハリー **が** ひとり占めできなかった?




This sentence is a bit irregular although most native speakers, myself
included, wouldn’t notice it unless someone specifically asks about it. What’s
irregular is that が makes us parse it this way.

> みんなが寄ってくるので、［教授がハリーをひとり占め］にはできなかった。

Syntactically, this is identical to this.

> みんなが寄ってくるので、［ひとり占め］にはできなかった。

Usually, if you want to specify who does the monopolization and who they
monopolize, you would make a sentence and turn it into a noun phrase, like
this.

> みんなが寄ってくるので、［教授がハリーをひとり占めにすること］はできなかった。

I would say the original sentence is a somewhat “sloppy” version of this
sentence. They mean the same thing.

〜を独り占めする and 〜を独り占めにする are practically interchangeable. In fact, the following
sentences both sound completely natural.

> みんなが寄ってくるので、［ひとり占め］はできなかった。

> みんなが寄ってくるので、［教授がハリーをひとり占めすること］はできなかった。

However, removing に from the original sentence makes it a bit weirder.

> ? みんなが寄ってくるので、［教授がハリーをひとり占め］はできなかった。

教授が and ハリーを, which are expected to modify some verb, seem more out of place
in the noun phrase in the brackets. I suppose に reminds us of the existence of
an omitted verb, namely する in the more complete version with a nominalized
sentence, and that makes the original sentence easier to understand the way it
is intended despite its “sloppiness.”

は singles out what the professor couldn't do among all things. I get a sense
of “even if they wanted to” from it.

Lastly, 教授はハリーがひとり占めできなかった would mean a completely different thing. Harry
would be the one monopolizing the professor.




Aをひとり占めする and Aをひとり占めにする are both correct and mean the same thing, "to keep A
all to oneself".

The former is a fairly simple transitive suru-verb. In this approach, you must
say 教授はハリー **を** ひとり占めできなかった because Harry is the simple direct object of
ひとり占めする. If you used が, the meaning of the sentence would change drastically
("Harry could not ...").

As for the latter, one way of understanding it would be to understand 独り占め
also as a descriptive noun (i.e., a no-/na-adjective) meaning "monopolized".
XをYにする works fine with adjectives (e.g., 問題を簡単にする, 壁紙を緑色にする). You can say
彼女によって独り占めの島 and 彼女が独り占めしている島 interchangeably (although the latter is more
common). Similar examples include:

  * **半殺し** : Aを半殺しする and Aを半殺しにする both mean "to half-kill A". 半殺しの人 and 半殺しされた人 mean "half-killed person".
  * **丸投げ** : Aを丸投げする and Aを丸投げにする both mean "to leave A entirely (to someone)". 丸投げの議題 and 丸投げされた議題 mean "the topic thrown (to someone)".

