Why is が used instead of を in this sentence?


From Shin Kanzen Master JLPT N1 Grammar:

あ、本が出しっぱなしだ。

I thought that 出す always follows を, i.e. you (subject) take out something
(object).

Is it because 本 is emphasized in this sentence, similar to how が is used
instead of を [with the potential form of a
verb](https://japanese.stackexchange.com/questions/609/the-difference-
between-%E3%81%8C-and-%E3%82%92-with-the-potential-form-of-a-verb)?

Or is it because 出しっぱなしだ as a whole acts more like an adjective that describes
the book?




You could say 出しっぱなし works _like_ an adjective in that sentence, or you could
also see 出しっぱなしだ as a shorter way of saying 出しっぱなしになっている. Either way, it
describes the state of the book and therefore the book deserves the subject’s
spot.

本を出しっぱなしだ is also possible. It means the same as 本を出しっぱなしにしている. This focuses
on someone’s earlier act on the book rather than the current state of the
book. The book is the object of the act in this case.




You could say 出しっぱなし works _like_ an adjective in that sentence, or you could
also see 出しっぱなしだ as a shorter way of saying 出しっぱなしになっている. Either way, it
describes the state of the book and therefore the book deserves the subject’s
spot.

本を出しっぱなしだ is also possible. It means the same as 本を出しっぱなしにしている. This focuses
on someone’s earlier act on the book rather than the current state of the
book. The book is the object of the act in this case.

