While studying ばかりだ I found in a grammar book the following example:

> 日本語の成績が下がるばかりだ。

It was also written that in this sentence ばかりだ cannot be substituted by 一方だ,
but searching on the internet I found many sentences with 成績が下がる一方だ. Now, I'm
not sure if I didn't understand the difference between ばかりだ and 一方だ, or I read
the grammar book incorrectly. Can somebody clarify it to me?
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2019-07-06T19:15:31.557
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2019-07-10T13:01:26.367
2019-07-06T22:50:10.490
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question
grammar
Is this sentence grammatically correct?
I don’t know the Japanese grammar correctly. but as a native Japanese speaker,
成績が下がる一方だ is very natural.  
I also search internet , most japanese article says it’s correct.
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2019-07-06T19:39:45.093
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2019-07-06T19:39:45.093
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answer
IMHO both 日本語の成績が下がるばかりだ and 日本語の成績が下がる一方だ are perfectly fine because it's
about an undesirable change.

  * 一方だ only refers to a temporal change, whereas ばかりだ can refer to a bad thing happening many times (≒"always"). 

> × 迷惑をかける一方で申し訳ない。  
>  ○ 迷惑をかけるばかりで申し訳ない。

  * ばかり almost exclusively describes an undesirable change, whereas 一方だ can also refer to a good change. 

> ○ 彼の日本語の成績は上がる一方だ。  
>  × 彼の日本語の成績は上がるばかりだ。
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2019-07-08T22:57:12.753
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