一方(いっぽう)だMore and more, Continue to, Keep on, -er and -er

どんどん is an adverb that implies rapid or dramatic change, often in leaps and bounds, and is common in everyday speech. In contrast, 一方だ is more formal and used to describe ongoing change that continues beyond the speaker's control. Structurally, 一方だ follows the verb, unlike どんどん, which appears before it.

Both can be used to describe change, but with different patterns. ば〜ほど expresses a proportional relationship between two things, like 'the more (A), the more (B)', e.g. 練習すればするほど上手になる ('The more you practice, the better you get.') 一方だ shows a continuous, one-way change in a single direction, e.g. 物価は上がる一方だ ('Prices just keep rising.')

ばかりだ and 一方だ are similar in that both express continuous or progressive change. However, ばかりだ is typically used with negative developments and often carries a more subjective tone, e.g. 状況は悪くなるばかりだ ('The situation keeps getting worse'). 一方だ, on the other hand, sounds more neutral or objective, and doesn't necessarily imply a negative trend, e.g. 人口は増える一方だ ('The population keeps increasing').

Both 一方だ and ますます express progressive change, but differ in usage. 一方だ follows verbs, often in formal or objective contexts to describe trends, e.g. '物価は上がる一方だ' ('Prices keep rising'). ますます has a similar nuance, but precedes the phrase or sentence, e.g. '彼の人気はますます高まっている' ('His popularity is increasing more and more').

Both 一方だ and いよいよ express change, but differ in usage. 一方だ follows verbs, often in formal or objective contexts to describe trends, e.g. '物価は上がる一方だ' ('Prices keep rising'). いよいよ suggests something is finally or imminently happening, often with anticipation, e.g. 'いよいよ試合が始まる' ('The match is about to begin').

While they look similar, 一方で and 一方だ serve different functions. 一方で shows contrast between two ideas or situations, e.g. '一方で反対する人もいる' ('On the other hand, some people are against it'). 一方だ follows verbs to describe trends, e.g. '物価は上がる一方だ' ('Prices keep rising').

つづける and 一方だ both indicate continuation but differ in tone. つづける means a simple ongoing action, e.g. 減り続けている 'is still decreasing'. 一方だ follows dictionary-form verbs and adds a sense of progression in one direction, often negatively, e.g., 減る一方だ 'is getting worse and worse'.