Is Facebook's use of double が grammatically unambiguous?


Facebook has issued me the following alert:

> Aさんが、Bさんがあなたとシェアした写真について「いいね！」と言っています

I think this is a translation of "A likes the photo that B shared with you."

Is it obvious what's being said? Why couldn't it be read as both A and B
liking the photo?




Actually, this kind of "double が" situation happens all the time. Sometimes
there's just no elegant way around it. In this case, Aさんは doesn't feel exactly
right because these notifications appear out of the blue with no surrounding
context. In cases where brand new information is coming in, が usually feels
better in introducing it. Imagine it sort of like an announcement of a radar
contact: "Sir! A meteor has been detected on the starboard side!" This would
definitely be が. The Facebook notification is very similar in feeling.

I admit that I too feel a tinge of worry when I'm forced to use this sort of
construction, but I've never seen a native speaker have any trouble
understanding these.

**Edit** : Sorry, I didn't answer your actual question:

> Why couldn't it be read as both A and B liking the photo?

If both people liked the photo, the sentence would be more explicit about
that. It would look something more like:

AさんもBさんも、Bさんがあなたとシェアした写真について「いいね！」と言っています。

On the other hand, if only B liked the photo that B himself shared, it would
like be simply:

Bさんが、あなたとシェアした写真について「いいね！」と言っています。

The fact that two parties are mentioned makes the reader expect that one of
them lives in a relative clause. So it is natural to expect that A is the main
subject of the sentence.




Actually, this kind of "double が" situation happens all the time. Sometimes
there's just no elegant way around it. In this case, Aさんは doesn't feel exactly
right because these notifications appear out of the blue with no surrounding
context. In cases where brand new information is coming in, が usually feels
better in introducing it. Imagine it sort of like an announcement of a radar
contact: "Sir! A meteor has been detected on the starboard side!" This would
definitely be が. The Facebook notification is very similar in feeling.

I admit that I too feel a tinge of worry when I'm forced to use this sort of
construction, but I've never seen a native speaker have any trouble
understanding these.

**Edit** : Sorry, I didn't answer your actual question:

> Why couldn't it be read as both A and B liking the photo?

If both people liked the photo, the sentence would be more explicit about
that. It would look something more like:

AさんもBさんも、Bさんがあなたとシェアした写真について「いいね！」と言っています。

On the other hand, if only B liked the photo that B himself shared, it would
like be simply:

Bさんが、あなたとシェアした写真について「いいね！」と言っています。

The fact that two parties are mentioned makes the reader expect that one of
them lives in a relative clause. So it is natural to expect that A is the main
subject of the sentence.

