Why is の placed after the object and before を here?


Why is の used here after the object in this sentence? Can it be omitted and
still have the same meaning “Why didn't you buy the right size?”

> どうしてちょうどいい大きさ **のを** 買わなかったの？

Obviously, it's not a verb nominalized. By meaning, it substitutes something
like Tシャツ but it not a substitution for a noun like Aいの (e.g., 大きいのです).




Other than the usage as a verb/adjective nominalizer, the particle の that
follows a noun (or noun phrase) acts like a noun, just as if もの is omitted
right after the particle. So here ちょうどいい大きさの can be interpreted as
ちょうどいい大きさのもの “the one of the right size”

> どうしてちょうどいい大きさを買わなかったの？

The variation where の is also omitted is sometimes heard in daily
conversation, but it allows strange interpretation “buy size itself” as well
and thus sometimes confusing.




Other than the usage as a verb/adjective nominalizer, the particle の that
follows a noun (or noun phrase) acts like a noun, just as if もの is omitted
right after the particle. So here ちょうどいい大きさの can be interpreted as
ちょうどいい大きさのもの “the one of the right size”

> どうしてちょうどいい大きさを買わなかったの？

The variation where の is also omitted is sometimes heard in daily
conversation, but it allows strange interpretation “buy size itself” as well
and thus sometimes confusing.

