～だろう
probably or surely
～だろう is the plain conjectural ending. It follows the plain form of a verb or い-adjective, or attaches directly to a noun or な-adjective (without だ), and marks the sentence as the speaker’s guess or supposition.
It maps to English “probably” or “I suppose”. It is the plain-style counterpart of polite ～でしょう, so it is common in writing and in casual speech.
1. Making a guess
Add だろう to a statement to show you believe it is true but are not certain.
明日は晴れるだろう。
“It will probably be sunny tomorrow.”
- 明日（あした）= tomorrow
- は = topic marker
- 晴れる（はれる）= to clear up, become sunny
- だろう = probably (speaker’s guess)
2. Guessing about something you cannot check
～だろう also works for past events, when you are inferring what must have happened.
彼はもう家に着いただろう。
“He has probably arrived home by now.”
- 彼（かれ）= he
- は = topic marker
- もう = already
- 家（いえ）= home, house
- に = destination marker
- 着いた（ついた）= arrived
- だろう = probably
How to form it
Plain form + だろう; for nouns and な-adjectives, attach だろう directly (drop だ).
- 晴れる（はれる）= to clear up → 晴れるだろう（はれるだろう）= will probably clear up
- 寒い（さむい）= cold → 寒いだろう（さむいだろう）= is probably cold
- 雨（あめ）= rain → 雨だろう（あめだろう）= is probably rain
Key idea
～だろう softens a statement into a prediction: the speaker is fairly confident, but is presenting it as a guess rather than a fact. When you need to be polite, switch to ～でしょう.
Built on the same stem
Updated .