Learn Hardcore Japanese: sensei ha gakusei ni kanzi wo kakaseru. - The teacher makes the students write kanji.

書かせる is the causative form of 書く, meaning “to make someone write” or “to let someone write.” It shows that the teacher causes the student to write kanji.

How do you form the causative for a verb like 書く?

For u-verbs (like 書く):

Change the final -u vowel to the -a vowel (書く → 書か)
Add せる: 書か + せる = 書かせる
For ru-verbs, drop る and add させる (食べる → 食べさせる).
Irregulars: する → させる, 来る → 来させる.

Why is 学生 marked with に instead of を?

In a causative construction, the person who is made or allowed to do something gets the particle に (or occasionally から in passive-style speech). The original verb’s object remains marked with を. So 学生に marks the one who writes.

What role does 漢字を play here?

漢字を is the direct object of the base verb 書く—it shows what the student is writing. We still use を for the thing being acted on, even in causative sentences.

How can you tell if this causative means “make” (force) or “let” (permit)?

Japanese causative covers both “make” and “let.” Context is key:

To emphasize permission (“let”), you might say 書かせてあげる (I let/allow them to write).
To stress compulsion (“make”), plain 書かせる or adverbs like 無理やり can be used.
The speaker’s attitude and surrounding words clarify the nuance.

How would you say this sentence in polite form?

Change 書かせる to its polite ending 〜ます:
先生は学生に漢字を書かせます。

What is the passive counterpart of this sentence (“The students are made to write Kanji by the teacher”)?

In passive causative you say:
学生は先生に漢字を書かされる。
This literally means “The students are made to write kanji by the teacher.”

What’s the difference between using は and が with 先生 here?

Using 先生は marks the teacher as the topic, hinting we’re talking about what the teacher does.
If you say 先生が学生に漢字を書かせる, you’re simply stating who does the action (subject-focus). The nuance is subtle:

は often contrasts or sets the scene (As for the teacher, …).
が is more neutral, just identifies the doer (the teacher does it).