Make a polite guess or seek agreement (でしょう / だろう)

The Mental Model: Softening Certainty with Buffer Space

In Japanese communication, stating an unverified fact with categorical certainty (です) can feel overly blunt or aggressive. If you are not 100% certain, or if you want to leave room for the other person's perspective, でしょう provides polite conjectural buffer space: “It is probably so,” or “I presume.”

• 明日は雨が降るでしょう: “It will likely rain tomorrow.” (Objective conjecture).
• 田中さんはまだ会社にいるでしょう: “Tanaka is probably still at the office.”

Two Intonations, Two Completely Different Meanings

Just like ね, the pitch contour on でしょう completely shifts its grammatical function:

• 1. Falling Intonation (でしょう↘): Objective Polite Conjecture (Around 70–80% probability).
• Used in weather forecasts, news reports, and polite professional hypotheses.
• 午後から晴れるでしょう: “It will likely clear up in the afternoon.”
• 2. Rising Intonation (でしょう↗): Seeking Agreement or Confirmation.
• Functions like an elevated tag question: “Right? Isn't that so?”
• あなたもそう思うでしょう？: “You think so too, don't you?”

The Casual Twin: だろう

でしょう is the polite form. Its plain/casual equivalent is だろう:

• Casual speech among friends (common in male speech): 明日は雨だろう (“It'll probably rain tomorrow”).
• Internal monologue (thinking to yourself): どうしてだろう (“Why would that be, I wonder?”).
• Written journalism and non-fiction: 今後も増加するだろう (“It will likely continue to increase”).

Connection Rules: The Dropped だ Trap

Pay close attention to how words connect to でしょう:

• Verbs (Plain form): Connect directly.
• 行くでしょう (will probably go), 来ないでしょう (probably won't come).
• い-adjectives — Plain form: Connect directly.
• 高いでしょう (probably expensive), 寒くないでしょう (probably not cold).
• Nouns & な-adjectives: Drop the affirmative copula だ before attaching でしょう!
• Noun: 学生でしょう (NOT *学生だでしょう).
• な-adjective: 静かでしょう (NOT *静かだでしょう).

The Social Hazard: The Smug “Told You So!”

When spoken casually with a rising intonation and a triumphant grin (でしょう！？), it transforms into: “See? I told you so!”

While fine when teasing friends, saying でしょう？ with a smug rising pitch to a teacher, customer, or workplace senior sounds arrogant and disrespectful. Keep your tone neutral in professional settings.