The causative form says that someone causes another person to do something. It has two main uses: making someone do it (an order, even if they do not want to) and letting someone do it (permission for what they want to do). The form is the same, so the context tells you which one it is; 〜させてくれる / 〜させてあげる usually show permission. It is normally used from a higher position to a lower one, such as parent to child or manager to staff.
§1Structure
Group I (五段): change the final -u sound to the -a sound + せる (書く → 書かせる, 読む → 読ませる, 待つ → 待たせる, 行く → 行かせる; verbs ending in う become わせる: 言う → 言わせる, 使う → 使わせる). Group II (一段): drop る + させる (食べる → 食べさせる, 見る → 見させる). Group III: する → させる, 来る → 来させる (こさせる). Every causative verb conjugates as a Group II verb (食べさせます, 食べさせない, 食べさせた, 食べさせて). Sentence pattern: with an intransitive verb, [causer] は + [doer] を + causative verb; with a transitive verb, [causer] は + [doer] に + [object] を + causative verb.
§2Examples
母は弟に野菜を食べさせました。
はははおとうとにやさいをたべさせました。
My mother made my younger brother eat vegetables.
先生は学生を立たせました。
せんせいはがくせいをたたせました。
The teacher made the students stand up.
父はわたしに好きな仕事を選ばせてくれました。
ちちはわたしにすきなしごとをえらばせてくれました。
My father let me choose the job I liked.
部長は田中さんを大阪へ行かせた。
ぶちょうはたなかさんをおおさかへいかせた。
The department manager sent Mr. Tanaka to Osaka.
お子さんにスマホを使わせていますか。
おこさんにスマホをつかわせていますか。
Do you let your child use a smartphone?
わたしは子どもに夜遅くまでゲームをさせません。
わたしはこどもによるおそくまでゲームをさせません。
I don't let my children play video games until late at night.
長い時間待たせて、すみませんでした。
ながいじかんまたせて、すみませんでした。
I'm sorry I kept you waiting for a long time.
娘が習いたいと言ったので、ピアノを習わせている。
むすめがならいたいといったので、ピアノをならわせている。
My daughter said she wanted to learn, so I am letting her take piano lessons.
§3Common mistakes
- Using を twice with a transitive verb. 母は弟を野菜を食べさせました is wrong. When the verb already has an object with を, the person who does the action takes に: 母は弟に野菜を食べさせました.
- Mixing up せる and させる. Group I verbs take せる after the -a sound, and Group II verbs take させる: 書かさせる and 食べせる are wrong. The correct forms are 書かせる and 食べさせる.
- Using the causative for someone above you. 先生を来させました sounds as if you gave the teacher an order, which is rude. When a higher person does something for you, use 〜ていただく or 〜てもらう: 先生に来ていただきました.
§4How it's different from similar grammar
- Passive form (れる / られる)
- The forms look similar, so check the sound after the -a: 読ませる is causative and 読まれる is passive. In a causative sentence the subject gives the order and the に-person does the action: 先生は学生に本を読ませました (The teacher made the students read a book). In a passive sentence the subject receives the action and the に-person does it to them: わたしは妹に日記を読まれました (My diary was read by my sister).
- てもらう (have someone do something as a favor)
- Both can be translated as 'have someone do', but the relationship is different. The causative is an order or permission from above: 兄は弟に荷物を運ばせました (The older brother made his younger brother carry the luggage). てもらう is a favor that the speaker is thankful for, and it can be used with anyone: 友だちに荷物を運んでもらいました (I had my friend carry the luggage for me).
§5How this shows up on the JLPT
N4 grammar questions often give four forms of one verb (causative, passive, potential, plain) and ask which fits, so decide who gives the order and who does the action. Particle questions test を for the doer with intransitive verbs and に with transitive verbs. In sentence-ordering questions, the usual order is '[causer] は → [doer] に → [object] を → causative verb'. The causative also appears inside longer expressions such as 〜させてください and 〜させてくれる, which are frequent in listening.
§6Quick check (3 questions)
1. Which is the causative form of 待つ?
まつ
2. Choose the particle that fits the blank: 先生は学生＿＿作文を書かせました。
せんせいはがくせい＿＿さくぶんをかかせました。
3. Which sentence correctly says 'My mother made my younger brother clean his room'?