Possibility and Probability in Japanese: でしょう, かもしれません, はずです, だろう
Welcome! In this guide, we are going to explore how to express uncertainty, probability, and logical expectation in Japanese. Whether you are writing an essay in Paper 2, tackling a nuanced translation in Paper 1, or listening to an interview in Paper 3, choosing the right degree of certainty is vital for scoring top marks at Edexcel A Level.
Don't worry if these structures feel similar at first. By the end of this guide, you will know exactly how to select the right expression based on probability percentage, register, and grammatical connections.
---1. The Probability & Certainty Scale
Think of probability in Japanese like a weather forecast. You wouldn't say "it will definitely rain" if there's only a slight drizzle predicted. Japanese uses specific sentence endings depending on how sure the speaker feels:
1. はずです / はずだ (~90–95% Certainty): Logical expectation. "Should be", "ought to be", "bound to happen" based on facts, evidence, or prior arrangements.
2. でしょう / だろう (~70–80% Probability): Strong conjecture or educated guess. "Probably", "I expect", "most likely".
3. かもしれません / かもしれない (~30–50% Possibility): Low-to-moderate possibility. "Might", "may", "could be".
Quick Summary Table:
• はずです (polite) / はずだ (plain): ~90–95% — Objective expectation based on logic/evidence
• でしょう (polite) / だろう (plain): ~70–80% — Subjective probability / educated guess
• かもしれません (polite) / かもしれない (plain): ~30–50% — Possibility / conjecture without certainty
2. Step-by-Step Breakdown: Formation and Usage
Structure 1: でしょう (Polite) & だろう (Plain)
Degree of Certainty: ~70–80% (High probability)
English Equivalents: "Probably", "most likely", "I think / expect"
Use でしょう in polite speech and だろう in plain-form writing (such as your Paper 2 literature/film essays) or informal conversations.
Formation Rules:
• Verbs (Plain Form): Plain dictionary / past / negative + でしょう / だろう
Example: 明日雨が降るでしょう (It will probably rain tomorrow).
• い-Adjectives: Plain form + でしょう / だろう
Example: 試験は難しいだろう (The exam will probably be difficult).
• な-Adjectives: Stem only (drop だ / な) + でしょう / だろう
Example: 図書館は静かでしょう (The library is probably quiet).
• Nouns: Noun only (drop だ) + でしょう / だろう
Example: 彼は日本人だろう (He is probably Japanese).
Key Takeaway: Never put だ before でしょう or だろう! Say 日本人だろう, never 日本人だだろう.
---Structure 2: かもしれません (Polite) & かもしれない (Plain)
Degree of Certainty: ~30–50% (Possibility)
English Equivalents: "Might", "may", "perhaps / possibly"
Use this when something is possible, but you are far from certain. In casual spoken Japanese, this is sometimes shortened to just かも.
Formation Rules:
• Verbs (Plain Form): Plain dictionary / past / negative + かもしれません
Example: 電車が遅れるかもしれません (The train might be delayed).
• い-Adjectives: Plain form + かもしれません
Example: 値段が高いかもしれない (The price might be high).
• な-Adjectives: Stem only (drop だ / な) + かもしれません
Example: 彼は暇かもしれません (He might be free).
• Nouns: Noun only (drop だ) + かもしれません
Example: これは偽物かもしれない (This might be a fake).
Key Takeaway: Just like with でしょう, attach directly to the noun or な-adjective stem without adding だ or な.
---Structure 3: はずです (Polite) & はずだ (Plain)
Degree of Certainty: ~90–95% (Logical Expectation)
English Equivalents: "Should be", "ought to be", "is expected to"
はず acts grammatically like a noun. Because of this, it follows noun-modifying rules (the same rules you use before words like ひと or こと). You use it when you have a solid, logical reason to believe something will happen.
Formation Rules:
• Verbs (Plain Form): Plain form + はずです
Example: 荷物は今日届くはずです (The package is supposed to / should arrive today).
• い-Adjectives: Plain form + はずです
Example: この映画は面白いはずだ (This film ought to be interesting).
• な-Adjectives: Stem + な + はずです (Notice the な!)
Example: 彼は日本語が上手なはずです (He should be good at Japanese).
• Nouns: Noun + の + はずです (Notice the の!)
Example: 今日は日曜日のはずです (Today should be Sunday).
Negative and Impossibility Forms:
• Logical Non-expectation: 〜ないはずです ("It is expected that [X] will not happen")
• Complete Impossibility: 〜はずがありません / 〜はずがない ("There is no way that...", "It cannot be that...")
Key Takeaway: Remember that はず needs な for な-adjectives and の for nouns!
---3. Summary of Connecting Patterns
Here is a quick reference trick to keep the connection rules straight:
• Verb (Plain): 書く + でしょう / かもしれません / はずです
• い-Adj: 高い + でしょう / かもしれません / はずです
• な-Adj: 静か + でしょう / かもしれません BUT 静かな + はずです
• Noun: 学生 + でしょう / かもしれません BUT 学生の + はずです
Memory Trick: Think of はず as a real noun. Just as you say 「静かな部屋」 and 「学生の本」, you must say 「静かなはず」 and 「学生のはず」!
---4. Common Pitfalls & Examiner Tips
Examiners frequently highlight the following recurring errors in Paper 1, Paper 2, and Paper 3:
1. The "Particle Insertion" Mistake
• Incorrect: ✕ 静かだでしょう / ✕ 学生だかもしれません
• Correct: ○ 静かでしょう / ○ 学生かもしれません
• Incorrect: ✕ 元気はずです / ✕ 先生はずです
• Correct: ○ 元気なはずです / ○ 先生のはずです
2. Register Mismatch in Essays and Translations
In Edexcel Paper 2 essays, you must write in a consistent register (typically the plain/da-form). Do not mix polite forms (でしょう, かもしれません, はずです) with plain endings in the same essay. Use だろう, かもしれない, and はずだ instead.
3. Misusing はずです for Personal Obligations / Advice
In English, we say "I should study tonight." However, in Japanese, はずです indicates logical expectation, not moral duty or personal intention. For personal obligation, use structures like 〜べき or 〜たほうがいい.
4. Translation Accuracy (Paper 1 & Paper 2)
• If the English text says "It might rain", translate it using 降るかもしれません (~30–50%), not 降るでしょう.
• If the English text says "He should know the answer" (based on his background/knowledge), translate it using 知っているはずです (~90–95%), not 知っているだろう.
5. Quick Review Checklist
✓ Is the likelihood low-to-medium (30–50%)? Use かもしれません / かもしれない.
✓ Is it a likely conjecture (70–80%)? Use でしょう / だろう.
✓ Is it a logical expectation based on clear evidence (90–95%)? Use はずです / はずだ.
✓ Did you add な to な-adjectives and の to nouns before はず?
✓ Did you remove だ before でしょう and かもしれません?