Lesson 48: Expectation with わけ, はず, べき, べし, ものだ, かもしれない

わけ is a noun meaning "reason" (as in "why"). At the end of a statement, it says a reason for something was identified through deduction/judgment.

Use one: the speaker knows something that's relevant, and they're making a statement to put emphasis on the fact that it's true and relevant right now. According to that fact or reason, something else is to be expected.

つまり、私たちは餌というわけですね

Basically, it's a matter of fact that we're food.

(There's a reason to know that we're food)

You can imagine that they're in trouble or there's something wrong with them.

Use two: one thing leads to another, based on fact. When negated, you can think of it as a way to refute an expectation that didn't follow good reasoning.

魔術師の家系の子供は、それだけで魔術に適した人間ってわけ。

That reason alone is why the children of magical lineages are suited to magic.

年齢でクラスが決まってるわけじゃないの。

There's no reason for classes to be decided based on age.

はず expresses that the speaker expects something to factually be true or come true. The english "should" expresses both this and "subjective" expectation, i.e. that it would be bad otherwise, so it's not a 1:1 match. はず also implies that the expectation is based on reasoning and is not pure conjecture.

高かったはずだ It must've been expensive.

優しいはずだ She should be kind. (I'm pretty sure she's kind)

べき states that the speaker expects a certain action or state, because otherwise it would be bad, irresponsible, etc.

When in the past tense like べきだった (or similar), it says that an action or state "was" or "would have been" right, usually the latter.

べし is an archaic version of べき. You're unlikely to run into it, but you never know with fiction.

ものだ can also express "should" with the nuance that it's a general "should" that applies to a lot of people, not just a specific person or a group. This only applies when it's being used for mood reasons, just like のだ. You should also watch out for ものを, another confusing use of もの.

かもしれない is a compound sentence-ending particle. It attaches the same way as か alone does. It expresses that the speaker thinks the statement is a possibility. Sometimes people attach this to things they know are true for politeness's sake.

悪質ではあるかもしれないけど―― Though it may be volatile...