一方だ【いっぽうだ】

一方だ says a change keeps going in one direction: "more and more", "just keeps getting…". It follows the dictionary form of a verb of change – ふえる増える, へる減る, あがる上がる, or an adjective with なる.

The trend is usually an unwelcome one, but a good one works too.

The verb stays in the dictionary form whatever the tense. The past goes on だ.

• × 悪くなった一方だ → 悪くなる一方だった

一方で in the middle of a sentence

Before another clause, 一方だ becomes 一方で, which looks just like いっぽう一方で "while, on the other hand". After a verb of change, with a second clause that follows on rather than contrasts, it is this pattern: "keeps…, and".

一方だ or ばかりだ

ばかりだ attaches the same way and means the same. It leans harder towards a bad trend, so for a good one 一方だ is the safer choice.