Meaning & usage
一方だ (いっぽうだ) describes a change that keeps moving in one direction. Use it after the dictionary form of a verb of change, such as 増える (increase) or 減る (decrease). It can describe an ongoing trend rather than a single completed event.
To describe a changing adjective, use a verb form such as 高くなる一方だ (keeps getting more expensive), rather than attaching 一方だ directly to 高い. The polite ending is 一方です.
Keep this pattern separate from 一方で (on the other hand), which contrasts two aspects of a situation. The noun 一方 in 一方通行 (one-way traffic) also does not demonstrate this grammar pattern.
Example sentences 3
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使わないアプリが増える一方だ。
The number of apps I do not use keeps increasing.
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この店の客は減る一方です。
The number of customers at this shop keeps decreasing.
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修理を待つ間に、問題は大きくなる一方だった。
While we waited for repairs, the problem kept getting bigger.
In past JLPT papers
This came up in 5 past exam questions.
And 1 more test.
Words in these examples
Sources and content notes
This explanation and the original examples were corrected with AI assistance. Independent Japanese-language review is pending.