Parsing the sentence 書く人物の顔が頭に入っていないと効果はない


This sentence is from Death Note, specifically on how to use it.

This sentence is written in-universe using English. It states, “This note will
not take effect unless the writer has the person’s face in their mind when
writing his/her (the victim’s) name.”

I understand that 書く is modifying 人物, which would lead me to believe that 人物
is in reference to **the person writing**.

However, 人物 being the owner of 顔 would imply that 人物 is the person whose name
is **being written**.

What is going on, grammatically speaking? Is this sentence ambiguous to native
speakers? Would it be any more or less ambiguous without the story context of
Death Note?




Grammatically, this is an inherent ambiguity of Japanese relative clauses. A
Japanese relative clause works by changing the word order and **dropping** a
case particle like が, を or に, and therefore it may result in an ambiguous
phrase. This typically happens when both the subject and the object are
humans.

> 人物 **を** 書く。 (Someone) write the (name of the) person.  
>  書く人物 the person ((whose name) someone) writes / the person whose name is
> written  
>  (人物 is the object of 書く)

> 人物 **が** 書く。 A person writes (something).  
>  書く人物 the person who writes (something) / the writer  
>  (人物 is the subject of 書く)

For example, あげた人 can refer to either a giver or a receiver depending on the
context. From AがBをCに紹介する ("A introduces B to C"), you can construct 紹介する人,
which can be interpreted either as "someone who introduces B to C" (=A),
"someone who A introduces to C" (=B), or "someone who A introduces B to" (=C).

See also: [が in subordinate
clauses](https://japanese.stackexchange.com/q/30171/5010)

