Both だろう and でしょう express probability or conjecture in Japanese. They’re the same grammar at heart — just in different registers.
At a Glance
| Form | Register | Meaning | Example |
|---|---|---|---|
| だろう | Casual / plain | Probably / I guess | 雨が降るだろう |
| でしょう | Polite | Probably / it would seem | 雨が降るでしょう |
だろう — Casual Conjecture
Use だろう in casual conversation to express a guess or probability.
明日は晴れるだろう。 — It will probably be sunny tomorrow.
彼はもう帰っただろう。 — He’s probably already gone home.
Rising intonation on だろう (だろう↑) turns it into a seeking-agreement question.
でしょう — Polite Conjecture
でしょう is the polite form used in formal speech, news broadcasts, and when speaking to superiors.
明日は晴れるでしょう。 — It will probably be sunny tomorrow. (weather forecast style)
With rising intonation: 行くでしょう？ — You’re going, right? (seeking agreement, politely)
YukaI always hear でしょう on the weather forecast. Is that why it sounds formal?
ReiExactly! でしょう is standard for weather reports and news — very common in broadcast Japanese. In everyday conversation with friends, you’d use だろう or even just ね to express the same uncertainty.
YukaWhat about かもしれない? How is that different?
Reiだろう/でしょう = higher probability (probably ~70-90%). かもしれない = lower, more uncertain (might ~30-50%). Use かもしれない when you’re less sure.
Probability Scale
| Expression | Probability | English equivalent |
|---|---|---|
| 絶対に〜する | ~100% | Will definitely |
| きっと〜だろう | ~80-90% | Surely / certainly will |
| 〜だろう / でしょう | ~60-80% | Probably |
| 〜かもしれない | ~30-50% | Might / maybe |
| 〜かな (casual) | ~20-40% | I wonder if… |
Common Mistakes
| Wrong | Correct | Note |
|---|---|---|
| Using でしょう with close friends all the time | だろう or ね | でしょう sounds stiff in casual conversation |
| Mixing with かもしれない (same probability) | Different levels | だろう = more certain; かもしれない = less certain |
Quick Quiz
1. (Weather forecast tone) It will probably rain tonight. → 今夜は雨が降るでしょう
2. (Casual, to friend) He’s probably busy. → 彼は忙しいだろう
3. (Uncertain) She might come. → 彼女は来るかもしれない
Practice in the Comments!
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Keep Learning: Grammar Hub | かもしれない vs でしょう vs はずだ | そうだ — Hearsay vs Appearance
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