Start with a question:
明日の試験は難しい＿＿。
A. だろう B. でしょう C. Both work
The answer is C. だろう and でしょう mean almost the same thing — "probably, I suppose, right?" The only difference is formality.
Core Meaning: The Speaker's Conjecture
だろう / でしょう express the speaker's conjecture based on some evidence — not 100% certain, but reasonably confident:
-
山田さんはもう結婚しているだろう。 → Yamada-san is probably already married.
-
来週から忙しくなるでしょう。 → It'll probably get busy starting next week.
-
熱が下がりましたから、もう大丈夫でしょう。 → The fever's gone down, so it should be fine now.
だろう vs でしょう: Different Tone
| だろう | でしょう | |
|---|---|---|
| Formality | Casual | Polite |
| Nuance | Talking to yourself / among friends | Polite / formal situations |
| Common in | Daily chat, inner monologue | Weather forecasts, business, speaking to elders |
In short: だろう is plain form, でしょう is polite form — same relationship as「だ / です」.
Casual conversation
A：荷物、届いたかな？ B：もう届いただろう。 → It's probably arrived already. (casual, between friends)
Weather forecast
明日は全国的に晴れるでしょう。 → It will likely be sunny nationwide tomorrow. (formal, polite)
How to Attach
だろう / でしょう attach to the plain form of the sentence:
| Word type | Attachment | Example |
|---|---|---|
| Verb | Plain form + だろう | 行くだろう (will probably go) |
| い-adjective | Plain form + だろう | 寒いだろう (probably cold) |
| な-adjective | Stem + だろう | 静かだろう (probably quiet) |
| Noun | Noun + だろう | 雨だろう (probably rain) |
Note: For な-adjectives and nouns, do not add な or だ before だろう. ❌
静かなだろう→ ✅ 静かだろう ❌雨だだろう→ ✅ 雨だろう
でしょう follows exactly the same attachment rules — just replace だろう with でしょう.
Common Pairings
たぶん + だろう / でしょう
たぶん (probably) often pairs with だろう / でしょう to reinforce the conjecture:
たぶん明日は雨だろう。 → It'll probably rain tomorrow.
きっと + だろう / でしょう
きっと (surely) pairs for higher confidence:
きっと合格するでしょう。 → You'll surely pass.
Another Use: Seeking Agreement
でしょう has another common use — confirming with the listener, with rising intonation, like "right?":
この料理、おいしいでしょう？ → This dish is good, right? (You think so too, right?)
昨日は寒かったでしょう？ → Yesterday was cold, wasn't it?
This use only works with でしょう, not だろう (because you're addressing someone and need to be polite).
Self-Test
Q1. 「明日は＿＿暑くなるだろう。」 Which adverb fits most naturally?
A. かならず B. たぶん C. ぜんぜん
Show answer
B. たぶん. だろう expresses conjecture, so たぶん (probably) is the most natural fit. かならず (definitely) is too strong, ぜんぜん (not at all) is typically used with negatives.
Q2. A weather forecast says "It will probably rain tomorrow." Use だろう or でしょう?
Show answer
でしょう. Weather forecasts are formal public communication, so use the polite form でしょう. → 明日は雨が降るでしょう。
Q3. 「静か＿＿だろう」— do you add「な」in the middle?
Show answer
No. な-adjectives connect directly to だろう using just the stem: 静かだろう, not 静かなだろう.
Summary
- だろう / でしょう = conjecture (probably, I suppose, right?)
- だろう is casual, でしょう is polite
- Attach to plain form; な-adjectives and nouns drop な/だ
- でしょう can also seek agreement (right?)
- Common pairings: たぶん (probably) or きっと (surely)