How to tell them apart
はず expresses a confident expectation based on evidence or logic — you believe something is or was the case, like 高かったはずだ (I expect it was expensive). べきだ expresses a moral or logical judgment that something ought to be done or be the case, like あるべき所 (where it should be). The key distinction is that はず describes what you think is true, while べきだ describes what you think is right or desirable. Swapping them is unnatural: saying 高かったべきだ sounds wrong because it mixes expectation with obligation, and あるはずの所 changes a normative claim into a mere guess.
- はず Use はず when you are fairly confident something is or was true based on evidence.
- べきだ Use べきだ when expressing a judgment that something ought to be done or be so.
| Grammar point | Meaning | JLPT level |
|---|---|---|
| はず hazu | Speaker's natural assumption; something ought to be so | N4 |
| べきだ bekida | is supposed to; is morally right to do | N3 |
はず hazu
Speaker's natural assumption; something ought to be so
はず expresses the speaker's expectation that something is or should be the case, based on reasoning. It follows plain-form verbs and い-adjectives, な-adjectives and nouns with な, and combines with がない or もない to strongly deny that something could be true.
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そんなの、身体にとっていいはずがないじゃありませんか。
That can't be good for your health, can it?
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一週間でどれほどのことが学べるか、自分でもびっくりするはずだよ！
You'd be surprised what you can learn in a week.
べきだ bekida
is supposed to; is morally right to do
べきだ expresses that something is the right or proper thing to do, a duty or expectation. It attaches directly to the dictionary form of a verb (する can also appear as すべきだ). It is a strong judgment, so it suits advice, opinions and statements about what ought to be.
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母親たちは子どもに道路で遊ばせないようにするべきだ。
Mothers should keep their children from playing in the streets.
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老人のための国立の病院がもっとあってしかるべきだ。
There should be more national hospitals for old people.
はず and べきだ are JLPT N4–N3 grammar points that Japanese learners often mix up. This page compares them side by side on meanings, usage and example sentences, so you can tell them apart.