Deshou, Hazu and Beki: Probability and Obligation
English "should" is doing two unrelated jobs. "The train should arrive at six" is a prediction. "You should apologise" is an obligation. Nothing in the word tells you which, so English speakers carry the overlap into Japanese — and Japanese will not have it. Probability lives in one family of words — でしょう (deshou), だろう (darou), かもしれない (kamoshirenai), はず (hazu) — and obligation in another — べき (beki), なければならない (nakereba naranai) — and the two never mix.
This page covers both families, in order of how much you are claiming.
でしょう (deshou) / だろう (darou): probably
でしょう (deshou) and だろう (darou) are the same word in two registers. でしょう (deshou) is the polite form; だろう (darou) is the plain form used with friends, in writing, and in your own head.
| Polite | Plain | |
|---|---|---|
| Probably | でしょう (deshou) | だろう (darou) |
Both attach to plain-form clauses:
| Japanese | Meaning |
|---|---|
| 明日は晴れるでしょう (ashita wa hareru deshou) | It will probably be sunny tomorrow |
| 彼は忙しいでしょう (kare wa isogashii deshou) | He's probably busy |
| これは正しいでしょう (kore wa tadashii deshou) | This is probably right |
| 学生でしょう (gakusei deshou) | He's probably a student |
でしょう (deshou) is not a strong claim. It sits somewhere around "probably" or "I'd expect" — confident enough to say out loud, loose enough to be wrong. Japanese conversation is full of it for exactly that reason: asserting something flatly (明日は晴れです) sounds like you have privileged information, while でしょう (deshou) leaves room for the world to disagree.
Three uses worth separating
- Prediction: 明日は雨でしょう (ashita wa ame deshou, "it'll probably rain tomorrow")
- Confirmation, with rising intonation: そうでしょう？ (sou deshou?, "right? isn't that so?") — you are checking, not predicting
- Agreement or empathy, as でしょうね: 大変でしたでしょうね (taihen deshita deshou ne, "that must have been hard") — softening, sharing the feeling
The softer でしょうか (deshou ka) turns a guess into a polite question: これでいいでしょうか (kore de ii deshou ka, "would this be all right?").
The confidence ladder
| Expression | Confidence | Meaning |
|---|---|---|
| かもしれない (kamoshirenai) | low | maybe, might |
| でしょう / だろう (deshou / darou) | medium-high | probably |
| はずだ (hazu da) | high, evidence-based | should be, is supposed to be |
| に違いない (ni chigainai) | very high | must be, no doubt |
Two of these deserve a note. かもしれない (kamoshirenai, "might") is the doubt end of the scale and pairs with でしょう (deshou) constantly in real speech: 明日は晴れるかもしれません (ashita wa hareru kamoshirenai, "it might be sunny tomorrow"). And に違いない (ni chigainai, "must be") is the confident end — 彼はもう帰ったに違いない (kare wa mou kaetta ni chigainai, "he must have gone home already").
はず (hazu): it should be, because…
はず (hazu) is where English "should" as prediction usually lands, but it comes with a condition English does not state: はず (hazu) requires a reason. It means "given what I know, this must be the case."
| Japanese | What the reason is |
|---|---|
| 彼はもう着いたはずです (kare wa mou tsuita hazu desu, "he should have arrived by now") | He left hours ago |
| ここにあるはずだ (koko ni aru hazu da, "it should be here") | This is where I put it |
| 彼は来るはずです (kare wa kuru hazu desu, "he should be coming") | He said he would |
Formation: a plain-form clause plus はず (hazu); with nouns, 名詞 + の + はず (meishi + no + hazu) — 学生のはずです (gakusei no hazu desu, "he should be a student").
Three forms to know:
- はずがない (hazu ga nai) — "there is no way, impossible": そんなはずがない (sonna hazu ga nai, "that can't be right")
- はずだった (hazu datta) — "was supposed to": 昨日届くはずだった (kinou todoku hazu datta, "it was supposed to arrive yesterday") — with the strong implication it did not
- はずなのに (hazu na no ni) — "even though it should be": 安いはずなのに高い (yasui hazu na no ni takai, "it should be cheap, but it's expensive")
はず (hazu) is not a guess. 明日は雨のはずです (ashita wa ame no hazu desu) means you have a reason — a forecast you saw, a plan you were told about. If you are just guessing, that is でしょう (deshou). And はず (hazu) sounds odd about your own deliberate future actions: 私が行くはずです (watashi ga iku hazu desu) is strange because you do not need to infer your own plans; use 予定 (yotei) or つもり (tsumori) instead.
べき (beki): it ought to be done
べき (beki) is obligation — what is right, correct or expected of someone. It attaches to a dictionary-form verb, with one famous irregular:
| Verb | + べき |
|---|---|
| 行く (iku, "go") | 行くべき (iku beki, "should go") |
| 謝る (ayamaru, "apologise") | 謝るべき (ayamaru beki, "should apologise") |
| する (suru, "do") | すべき (su beki, "should do") — するべき also appears, すべき is the standard form |
| Japanese | Meaning |
|---|---|
| 学生は勉強すべきだ (gakusei wa benkyou su beki da) | Students should study |
| 謝るべきです (ayamaru beki desu) | You should apologise |
| そんなことは言うべきじゃない (sonna koto wa iu beki ja nai) | You shouldn't say that |
| もっと早く来るべきだった (motto hayaku kuru beki datta) | I should have come earlier |
Two things make べき (beki) sharper in Japanese than "should" in English. First, it is moral or principled, not practical — it passes judgement. Second, it is strong. Telling a friend もっと勉強すべきだ (motto benkyou su beki da, "you should study more") sounds like a scolding, which is why Japanese speakers usually reach for softer tools:
| Form | Strength | Use |
|---|---|---|
| 〜たほうがいい (ta hou ga ii) | advice | 早く寝たほうがいい (hayaku neta hou ga ii, "you'd better go to bed early") |
| 〜べき (beki) | principle, judgement | 嘘をつくべきではない (uso o tsuku beki de wa nai, "one shouldn't lie") |
| 〜なければならない (nakereba naranai) | necessity, external | 行かなければならない (ikanakereba naranai, "I have to go") |
| 〜ことになっている (koto ni natte iru) | rule, arrangement | ここでは静かにすることになっている (koko de wa shizuka ni suru koto ni natte iru, "you're supposed to be quiet here") |
If you want to give advice rather than deliver a verdict, 〜たほうがいい (ta hou ga ii) is the everyday choice. べき (beki) is for editorials, principles and the occasional moment where you mean it.
はず vs べき, in one table
| はず (hazu) | べき (beki) | |
|---|---|---|
| Category | expectation | obligation |
| Based on | evidence and reasoning | what is right |
| Question answered | "what is probably true?" | "what ought to be done?" |
| Subject | things and people alike | people, mostly the listener |
| Example | 彼は来るはずです (kare wa kuru hazu desu, "he should be coming") | 彼は謝るべきです (kare wa ayamaru beki desu, "he should apologise") |
| English trap | "should be" | "should do" |
The test: if the sentence is about what will turn out to be true, it is はず (hazu). If it is about what someone ought to do, it is べき (beki). はず (hazu) can never tell anyone to do anything, and べき (beki) can never describe a fact.
Common mistakes for English speakers
1. Using はず (hazu) for a bare guess. 明日は寒いはずです (ashita wa samui hazu desu) claims you have evidence. If you are simply predicting, use 明日は寒いでしょう (ashita wa samui deshou).
2. Translating "should have" as はずだった (hazu datta). This is the single most valuable trap on this page. "I should have studied" is 勉強すべきだった (benkyou su beki datta) — obligation, regretted. 勉強するはずだった (benkyou suru hazu datta) means "I was supposed to study" — a plan existed, and it did not happen. The English "should" hides which one you mean; Japanese forces the choice.
3. Using でしょう (deshou) about things you know. 私は日本人でしょう (watashi wa nihonjin deshou) is absurd — you know your own nationality. でしょう (deshou) is for things you are inferring, not things you know.
4. Missing the intonation split on でしょう (deshou). Falling でしょう (deshou) is a prediction; rising でしょう (deshou) is a request for confirmation. The words are identical, so the tune is the grammar. English does the same thing with "right?" — but it uses a separate word for it, so learners do not think to listen.
5. Using べき (beki) for practical advice. 病院に行くべきです (byouin ni iku beki desu, "you should go to the hospital") is not wrong, but it sounds like a moral instruction. 病院に行ったほうがいいです (byouin ni itta hou ga ii desu, "you'd better go to the hospital") is what a friend actually says.
6. Marking べき (beki) with a past tense verb. 行ったべき (itta beki) does not exist. べき (beki) follows the dictionary form only — 行くべき (iku beki) — and the past is carried by the copula: 行くべきだった (iku beki datta, "should have gone").
7. Using だろう (darou) in polite company. だろう (darou) is plain form. With a stranger, a teacher or a client it is でしょう (deshou). 明日は雨だろう said to your boss sounds curt, even though the meaning is identical.
8. Treating かもしれない (kamoshirenai) and でしょう (deshou) as interchangeable. 明日は雨でしょう (ashita wa ame deshou) is "probably rain"; 明日は雨かもしれない (ashita wa ame kamoshirenai) is "it might rain". The difference in confidence is the whole point of the sentence, and English speakers tend to flatten both into "maybe".
9. Forgetting that はず (hazu) needs a reason you could state. If you cannot finish the sentence "…because…", you want でしょう (deshou). はず (hazu) without a reason behind it sounds like you are bluffing about evidence.
Summary
Probability runs on a ladder: かもしれない (kamoshirenai, "might"), でしょう / だろう (deshou / darou, "probably"), はず (hazu, "should be — and here's why"), に違いない (ni chigainai, "must be"). Obligation is a separate family led by べき (beki, "ought to"), softened for daily use into 〜たほうがいい (ta hou ga ii). Keep them apart by asking one question: am I predicting the world, or prescribing behaviour? Prediction takes the probability ladder, prescription takes べき (beki).
These forms are how Japanese conversation stays non-committal, and the only way to feel the difference in confidence is to type them in context: romaji.live practice pairs でしょう with かもしれません in the same scene. Read tsumori and yotei next, since はず and 予定 sit close together, and see the polite form for the です / ます (desu / masu) endings these all attach to.
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