〜一方だ: 'Keeps Getting More and More'
A change that only heads one way
〜一方だ describes a change that is moving steadily in a single direction and shows no sign of reversing. Think of it as English "keeps getting more and more ~" or "just keeps ~ing." Because it paints a one-way slide, it very often carries a negative or worrying feeling: things keep getting worse, busier, more expensive. It can describe a good trend (成績は上がる一方だ), but if you just want a neutral "is increasing," the plain 〜ている form (増えている) usually sits better.
この町の人口は減る一方だ。
この まちの じんこうは へる いっぽうだ。
This town's population just keeps dropping.
減る (to decrease) is a change verb — perfect for 一方だ.
試験が近づいて、ヤッタンの不安は大きくなる一方だった。
しけんが ちかづいて、ヤッタンの ふあんは おおきく なる いっぽうだった。
As the exam drew near, Yattan's anxiety only grew and grew.
〜なる verbs (大きくなる) are textbook 一方だ material.
The verb has to name a trend
The word in front is almost always a change verb — 上がる, 増える, 悪くなる, 減る — something that names a direction of travel rather than a one-off event. That is why 食べる一方だ or 見る一方だ sounds off: eating and watching aren't directional changes. Reach instead for 増える, 減る, 上がる, 下がる, 悪くなる, 強くなる, and the 〜くなる / 〜になる family.
モチは新しい趣味を始めてから、出費が増える一方だ。
モチは あたらしい しゅみを はじめてから、しゅっぴが ふえる いっぽうだ。
Ever since Mochi took up a new hobby, his spending just keeps going up.
Attaching it: dictionary form, tense on だ
Attach 一方だ directly to the dictionary (plain present) form of that change verb. The verb itself never moves — it stays plain present — and any tense or politeness rides on だ.
| Element | Form | Example |
|---|---|---|
| Change verb (dictionary form) | Vる + 一方だ | 増える → 増える一方だ |
| 〜くなる / 〜になる | …なる + 一方だ | 悪くなる → 悪くなる一方だ |
| Past tense | 一方だった | 増える一方だった (kept increasing) |
| Polite | 一方です | 増える一方です |
The trap here is retiming the verb: it's 悪くなる一方だ (✓), never 悪くなった一方だ or 悪くなっている一方だ (✗). If you want the past, shift だ → だった and leave the verb alone.
In warnings and reports
Because it names an unstoppable slide, 一方だ is a natural fit for cautioning someone or relaying a trend you've heard about.
放っておくと、病人の容体は悪くなる一方ですよ。
ほうっておくと、びょうにんの ようたいは わるく なる いっぽうですよ。
If you leave it alone, the patient's condition will only get worse.
A typical warning use — the one-way change is undesirable.
先生によると、都会の人口は増える一方だそうだ。
せんせいに よると、とかいの じんこうは ふえる いっぽうだ そうだ。
According to the teacher, the urban population just keeps growing.
一方だ or 一方で?
Same kanji, two completely different jobs. 〜一方だ ends a sentence on だ/です and marks an escalating one-way change (上がる一方だ = "keeps rising"). 〜一方(で) sits mid-sentence and joins two coexisting facts as a contrast — "on the other hand / while" (彼は厳しい一方で、優しいところもある = "he's strict, but also has a kind side"). The swap-test settles it: if "more and more" fits, it's 一方だ; if "whereas" fits, it's 一方で. Note that a single sentence can even stack both, as when an escalating change meets a contrast clause.
物価は上がる一方で、給料は変わらない。
ぶっかは あがる いっぽうで、きゅうりょうは かわらない。
Prices keep rising, while wages stay the same.
Here 上がる一方 stacks an escalating change with a contrast clause.
The short version
- 〜一方だ = a change that keeps going one way, more and more — often negative.
- Attach it to a dictionary-form change verb: 増える / 減る / 悪くなる + 一方だ.
- Tense rides on だ: 一方だ → 一方だった → 一方です.
- Don't mix it up with 〜一方(で) ("on the other hand"), which is a contrast.
Practice it
Pick the sentence that uses 〜一方だ correctly for a one-way change.
＿＿＿に入れるのに最もよいものを選びなさい。
物価は＿＿＿。
Frequently asked questions
What's the difference between 一方だ and 一方で?
〜一方だ at the end of a sentence means a change keeps intensifying in one direction (物価は上がる一方だ = 'prices keep rising'). 〜一方(で) joins two clauses to mean 'on the other hand / while' (厳しい一方で、優しい = 'strict, yet kind'). Same 一方, completely different use.
Which verb form comes before 一方だ?
The dictionary (plain present) form: 増える一方だ, 悪くなる一方だ. Never the past or 〜ている form. Tense is shown on だ → だった instead.
Does 一方だ always sound negative?
Not always, but usually. It most naturally describes worsening or unstoppable trends. It can describe a positive trend too (成績は上がる一方だ), but for a plain 'is increasing' the 〜ている form is often more neutral.
Can I use 一方だ with any verb?
Only with change/trend verbs — 増える, 減る, 上がる, 下がる, 〜くなる, 〜になる. Action verbs like 食べる or 見る don't work because they don't describe a one-directional change.
Where 〜一方だ fits
Don't confuse it with
- 〜ば〜ほど · N3 — 〜ば〜ほど means 'the more X, the more Y.' Learn how to repeat verbs and adjectives in the ば-form + dictionary/plain + ほど pattern, with な-adjective and noun forms.
More N3 grammar to explore
Keep going with related patterns at the same level:
- 〜かけ / 〜かける — 〜かけ attaches to a verb stem to mean an action is started but unfinished: 食べかけのパン (half-eaten bread), 読みかけの本 (book I'm partway through), 死にかけた (nearly died).
- 〜うちに — 〜うちに means 'while a state lasts' — do something before it changes: 明るいうちに帰ろう. Learn 〜ないうちに ('before X happens'), 〜ているうちに, and うちに vs 間に.
- 〜ことだ — 〜ことだ gives direct, practical advice — 'the best thing is to' / 'you should.' Learn the formation, how it differs from べき and the nominalizer こと, and common mistakes.
- 〜まま — 〜まま means a state stays unchanged while something else happens: 電気をつけたまま寝た ('slept with the light on'). Learn た/ない/noun/adjective forms and そのまま.
- 〜ながら（も） — The concessive 〜ながら（も） means 'although / even though,' pointing out a contradiction between two facts about the same subject: 彼は忙しいながら、健康に気をつけない. Not to be confused with the 'while doing' ながら.
- 〜によると/によれば — によると and によれば both mean 'according to,' citing the source of information a sentence is based on (天気予報によると、明日は雨だそうだ). The sentence almost always ends in a hearsay form like そうだ or らしい.