Introduction
Have you ever wanted to say things like:
- “It will probably rain tomorrow.”
- “I think the economy will get better.”
- “He will surely be happy.”
In Japanese, when you want to express a guess, prediction, or probability, you can use:
～だろう / ～だろうと思う = probably… / I think it will…
Let’s learn how to use these natural Japanese expressions to share your predictions and thoughts.
1. Meaning: What does ～だろう mean?
～だろう (darou) has the exact same meaning as ～でしょう (deshou). It is used to express:
- a guess or presumption,
- a prediction about the future,
- probability.
Common English translations:
- probably…
- I guess…
- I think…
2. Formation
Basic structure
To use this grammar, simply attach だろう to the plain form of a verb, adjective, or noun.
Verb / い-adjective
Plain form + だろう
- 増える (to increase) → 増えるだろう
- 良い (good) → 良いだろう
な-adjective / Noun
Dictionary form (without だ) + だろう
- 元気 (energetic) → 元気だろう (NOT 元気なだろう, 元気だだろう)
- 雨 (rain) → 雨だろう (NOT 雨だだろう)
Examples by word type
| Type | Example |
|---|---|
| Verb | これからは外国人の旅行者が増えるだろう。 Foreign tourists will probably increase from now on. |
| い-adjective | この仕事は難しいだろう。 This job will probably be difficult. |
| な-adjective | 彼はきっと元気だろう。 He is surely doing fine (energetic). |
| Noun | 明日は雨だろう。 It will probably rain tomorrow. |
How to guess about the past
You can also use だろう to guess about something that already happened. Simply change the verb or adjective into the past tense (Ta-form) before adding だろう.
- 昨日は雨だっただろう。(It probably rained yesterday.)
- そのテストは難しかっただろう。(That test was probably difficult.)
Make it Sound Natural: Use たぶん and きっと
Native speakers often pair ～だろう with specific adverbs to show exactly how confident they are in their guess.
- たぶん (Probably) + だろう: Standard guess (~70% sure).
- たぶん、明日は雨だろう。(It will probably rain tomorrow.)
- きっと (Surely / Definitely) + だろう: Strong confidence (~90% sure).
- 彼はきっと喜ぶだろう。(I’m sure he will be happy.)
3. Spoken vs. Written Japanese (だろう vs だろうと思う)
It is important to know when to use ～だろう and when to use ～だろうと思う.
- ～だろう： Written Language (書き言葉)
Used in news articles, essays, and reports. It sounds objective and declarative. - ～だろうと思う： Spoken Language (話し言葉)
Used in daily conversations. Adding と思う softens the sentence and emphasizes that it is your personal opinion or guess.
Compare:
- これからは外国人の旅行者が増えるだろう。
Foreign tourists will probably increase. (Written) - 外国人の旅行者が増えれば、経済がもっと良くなるだろうと思います。
If foreign tourists increase, I think the economy will get better. (Spoken)
4. Watch Your Intonation! (Rising vs. Falling)
When using ～だろう in casual conversation, your intonation changes the entire meaning!
- Falling Intonation (だろう ⬇): Expresses a guess or prediction (Probably…).
- 明日は雨だろう ⬇ (It will probably rain tomorrow.)
- Rising Intonation (だろう？ ⬆): Seeking agreement or confirming a fact (…, right? / Didn’t I tell you?).
- 言っただろう？ ⬆ (I told you so, didn’t I?)
- これ、おいしいだろう？ ⬆ (This is delicious, right?)
5. Example Sentences
Written style (～だろう)
弟の誕生日にゲームを買ってあげるつもりだ。きっと喜ぶだろう。
I plan to buy my younger brother a video game for his birthday. I’m sure he’ll love it.
次のワールドカップはフランスが優勝するだろう。
France will probably win the next World Cup.
娘の成績が悪いのは、勉強時間が足りないからだろう。
My daughter’s poor grades are probably because she doesn’t study enough.
Spoken style (～だろうと思う)
この曲は人気が出るだろうと思います。
I think this song will probably become popular.
姉が幼なじみと結婚しました。二人はきっと幸せになるだろうと思います。
My older sister got married to her childhood friend. I’m sure they’ll be happy together.
田中さんなら、この仕事を手伝ってくれるだろうと思います。
I think Tanaka-san would be willing to help with this task.
6. Related grammar (comparison)
～だろう vs ～でしょう
In Japanese, you can show guess, probability, or prediction with: (short form) ＋ でしょう
Both expressions mean “probably” or “I suppose”, and in many situations they are interchangeable.
However, でしょう is more polite, while だろう is the plain form.
| Expression | Nuance |
|---|---|
| ～だろう | Plain / casual / often used in writing |
| ～でしょう | Polite / often used in conversation |
Examples:
- 明日は雨だろう。
It will probably rain tomorrow. - 明日は雨でしょう。
It will probably rain tomorrow. (more polite)
～だろう vs ～かもしれない
Both express uncertainty, but the degree of confidence is different.
| Expression | Meaning |
|---|---|
| ～だろう | Probably (~70–90%) |
| ～かもしれない | Maybe (~50%) |
Compare:
- 明日は雨だろう。
It will probably rain tomorrow. - 明日は雨かもしれない。
It might rain tomorrow.
The speaker is more confident when using ～だろう.
～だろう vs ～そうだ
These grammar patterns are both used for predictions, but the basis of the prediction is different.
- Based on something the speaker can directly observe.
- Often based on appearance or immediate evidence.
～だろう
- Based on reasoning, knowledge, experience, or general judgment.
Example:
- 空が暗い。雨が降りそうだ。（≒雨が降るだろう）
The sky is dark. It looks like it’s going to rain.
7. Practice
Translate the following sentences into Japanese using ～だろう or ～だろうと思います.
| Clue | Example Answer |
|---|---|
| It will probably rain tomorrow. | 明日は雨だろう（と思います）。 |
| I think this song will NOT become popular. | この曲は人気が出ないだろう（と思います）。 |
| I think France will win the World Cup. | フランスがワールドカップで優勝するだろう（と思います）。 |
| I think the economy will NOT improve. | 経済は良くならないだろう（と思います）。 |
| Tanaka-san will probably come tomorrow. | 田中さんは明日来るだろう（と思います）。 |
| I think this restaurant will become famous. | このレストランは有名になるだろう（と思います）。 |
| I think this project will succeed. | このプロジェクトは成功するだろう（と思います）。 |
| That test was probably difficult. | そのテストは難しかっただろう（と思います）。 |
| John probably didn’t attend that meeting. | ジョンはその会議に参加しなかっただろう（と思います）。 |
FAQ
- QWhat is the difference between だろう and でしょう?
- A
They mean the exact same thing, but their politeness level is different. でしょう is polite and can be used directly to listeners. だろう is the plain (casual) form. In formal speeches or polite conversations, you should use でしょう (e.g., 明日は雨でしょう).
- QCan I say ～だろうと思います in polite situations?
- A
Yes! Even though だろう is a plain form, because you end the sentence with the polite と思います, the whole sentence becomes polite. This is a common and natural way to express your opinion respectfully.
- QDoes ～だろう sound masculine?
- A
In spoken Japanese, ending a sentence simply with ～だろう (without と思う) can sound a bit masculine, blunt, or authoritative. Women often prefer to use ～かな or ～でしょう in casual speech. However, in written Japanese (essays, news), ～だろう is gender-neutral and used by everyone.
- QCan I use ～だろう with my boss?
- A
No, ～だろう is a plain form and sounds too casual or blunt for speaking directly to a superior. If you are talking to your boss, you should use the polite form ～でしょう or ～だと思います instead.
Conclusion
In this article, you learned how to use ～だろう and ～だろうと思う to express guesses, predictions, and probabilities.
- Use ～だろう for writing or objective predictions.
- Use ～だろうと思う in conversations to share your personal guess or opinion.
Mastering this grammar will help you express your thoughts and predictions naturally. Try using it the next time you predict the weather or talk about the future!
