Usage of のに in this sentence: じゃ、あたらしいのにかえましょう


Assuming the following sentence and its answer:

> にもつがおもくて、ふくろのひもがきれそうです。  
>  じゃ、あたらしいのにかえましょう。

I don't really understand why we have to use のに instead of を in the answer,
actually I'd have answered like this:

じゃ、あたらしいをかえましょう。which would mean "Then let's buy a new one".

The way I interpreted the usage of のに is more like "Then we'll have to buy a
new one." Is that correct or is there a more accurate translation?




あたらしいをかえましょう is ungrammatical. あたらしい is an adjective, and the object of a
sentence (thing marked by を) must be a noun or noun phrase.

あたらしい **の** をかえましょう would be grammatical but it would not have the correct
meaning. The の here means 'one' and makes the adjective into a noun phrase.
This sentence would mean "Let's change the new one". But, you want to change
**to** the new one, hence に rather than を.




あたらしいをかえましょう is ungrammatical. あたらしい is an adjective, and the object of a
sentence (thing marked by を) must be a noun or noun phrase.

あたらしい **の** をかえましょう would be grammatical but it would not have the correct
meaning. The の here means 'one' and makes the adjective into a noun phrase.
This sentence would mean "Let's change the new one". But, you want to change
**to** the new one, hence に rather than を.

