Overview
These two endings let you make a guess instead of stating a fact — “it’ll probably rain,” “he’s likely tired,” “that’s the one, right?” They are not two different meanings; they are one grammar at two politeness levels. でしょう is simply the polite form of だろう, the way です is the polite form of だ. Whatever だろう can do, でしょう does too — just more politely. The shorthand for students: だろう = plain/casual “probably ~”; でしょう = the same thing, polite. They trip learners up for two reasons. First, students assume the two words differ in meaning when they really differ only in politeness. Second, each of them quietly does two separate jobs — making a guess (“probably ~”) and asking for agreement (“~, right?”) — and which job is meant depends on your intonation, not on the word itself. The sections below untangle both. The entries lead with a simple example, then a funny one.
でしょう — “probably ~ / ~, right? (polite)”
Explanation
でしょう is the polite way to say you’re guessing rather than asserting. In its first job it means “probably / most likely ~”: 明日は雨でしょう (“it will probably rain tomorrow”). This is the language of weather forecasts, careful predictions, and any time you want to soften a claim into a likelihood instead of a hard fact. It pairs naturally with たぶん (“probably”): たぶん来るでしょう (“they’ll probably come”). In its second job, said with a rising tone, it turns into “~, right? / don’t you agree?” — seeking the listener’s agreement: おいしいでしょう？ (“it’s delicious, right?”), 疲れたでしょう？ (“you’re tired, aren’t you?”). Same word, two jobs, split by intonation: falling tone guesses, rising tone asks for a nod.
Grammatically, でしょう attaches to the plain form of whatever comes before it, and the attachment rules are worth pinning down. After a verb: plain form + でしょう (行くでしょう, 行ったでしょう, 降るでしょう). After an い-adjective: い-adj + でしょう (高いでしょう, 寒いでしょう). After a な-adjective: drop the な (静かだ → 静かでしょう, never 静かなでしょう). After a noun: the noun attaches directly with no だ (学生でしょう, 雨でしょう — not 学生だでしょう). This “no だ before でしょう” point is the single most common slip, so hold onto it: noun/な-adjective go in bare.
The register is polite and gender-neutral, at home in both speech and writing. The teaching anchor is the polite guess: でしょう softens a statement into a likelihood, or (rising) invites agreement, in a way that’s safe with anyone. It differs from だろう only in politeness — だろう is the plain-form version of the exact same grammar. If the student is being polite, or writing a forecast-style prediction, でしょう is the fit.
Examples
明日は寒いでしょう。 — It will probably be cold tomorrow.
🌤️ 天気予報の人が「明日は晴れでしょう」と言いました。だから、私はかさを持って行きませんでした。でも、その日、雨がたくさん降りました。 — The weather forecaster said, “It’ll probably be sunny tomorrow.” So I didn’t take an umbrella. But that day, it rained a lot.
Common mistake
Don’t insert だ before でしょう after a noun or な-adjective — でしょう already carries that job. ✗ 学生だでしょう is wrong; it’s 学生でしょう. ✗ 元気なでしょう is wrong; it’s 元気でしょう. And remember the intonation decides the meaning: 学生でしょう↘ (“they’re probably a student”) versus 学生でしょう↗ (“they’re a student, right?”). Flatten the wrong way and your guess becomes a question, or the reverse.
だろう — “probably ~ / ~, right? (plain)”
Explanation
だろう does everything でしょう does, but in the plain, casual register — it’s the form for talking to friends, for self-talk, and for plain-style writing. As a guess it means “probably ~”: 彼は来ないだろう (“he probably won’t come”), たぶん高いだろう (“it’s probably expensive”). As a rising-tone agreement-seeker it means “~, right?”: すごいだろう？ (“cool, right?”). One extra note on the “right?” use: because it’s blunt, だろう？ in casual speech can sound a bit rough or masculine, so many speakers soften it. But as a plain-style guess — especially in writing, like a novel or an essay — だろう is completely neutral and standard.
Grammatically, だろう attaches exactly like でしょう, to the plain form, with the same rules. Verb: 来るだろう, 降っただろう. い-adjective: 高いだろう, 寒いだろう. な-adjective: drop な (便利だ → 便利だろう). Noun: attach bare, no だ (学生だろう, not 学生だだろう). The two forms are grammatical twins from the neck down; only the head — だろう versus でしょう — changes to set the politeness. だろう comes from plain だ, でしょう from polite です, which is the whole story of their difference.
The register is plain/casual (speech among friends and self-talk) or plain-style writing. The teaching anchor is the plain guess: same meaning as でしょう, just informal. It differs from でしょう only in politeness level. If the student is speaking casually, thinking aloud, or writing in plain style, だろう is the fit; to be polite, switch to でしょう.
Examples
彼はもう寝ているだろう。 — He’s probably already asleep.
🍰 弟がケーキを作りました。「おいしいだろう？」と弟は言いました。でも、食べたら、とてもまずかったです。弟はさとうと塩をまちがえました。 — My little brother made a cake. “It’s delicious, right?” he said. But when I ate it, it tasted really bad. He’d mixed up the sugar and the salt.
Common mistake
Don’t double up the だ after a noun — だろう already contains it. ✗ 学生だだろう is wrong; it’s 学生だろう. And be aware of tone in casual speech: 行くだろう↘ is a neutral guess (“they’ll probably go”), but 行くだろう↗ as “you’re going, right?” can sound blunt or pushy to some listeners, so in polite company use でしょう↗ instead.
How to choose
—From here on, it will be available to members only—