Causative form

The causative form is used when a 'causer' influences a 'causee' to act. The basic sentence structure is: [Causer] は/が [Causee] に/を [Verb-causative].

1. Conjugation Rules:

• Group 1 (Godan): Change the final -u sound to the -a sound and add 〜せる.
  Example: 行く（いく）→ 行かせる (make/let go).
  Note: For verbs ending in a vowel + う (like 買う（かう）), use わ: 買わせる.
• Group 2 (Ichidan): Remove 〜る and add 〜させる.
  Example: 食べる（たべる）→ 食べさせる (make/let eat).
• Group 3 (Irregular): する becomes させる; 来る（くる） becomes 来させる（こさせる）.

2. Particle Usage:
The particles change depending on whether the base verb is transitive or intransitive:

• Transitive Verbs: The causee is marked with に to avoid having two を particles.
  Example: 子供に本を読ませる (Make the child read a book).
• Intransitive Verbs: For living beings with volition, you can often use either を or に. Using に focuses on the causee as an agent with their own volition, while を treats the causee more as a direct object of the causer's action. While some beginner textbooks teach a simplified rule that を means coercion and に means permission, in reality, both can be used for permission or coercion depending on context.
  Example: 子供を走らせる vs. 子供に走らせる (Make/let the child run). For inanimate objects or things without volition, you must use を.
  Example: 車を走らせる (Drive/make the car run).
  Note 1: For verbs expressing emotion or involuntary actions (like 泣く（なく） or 驚く（おどろく）), the causee must be marked with を.
  Example: 親を泣かせる (Make one's parents cry).
  Note 2: If the intransitive verb already takes a location or path marked by を (e.g., 道（みち）を歩く（あるく）), the causee must be marked with に to avoid having two を particles.
  Example: 子供に道を歩かせる (Make/let the child walk down the street).
  Note 3: If a dedicated lexical transitive verb already exists (e.g., お湯を沸かす - boil water, 車を止める - stop a car), you must use it instead of the causative form of the intransitive verb (e.g., do not use 沸かせる or 止まらせる). This is because lexical transitives are used when the subject directly performs the action on an object, whereas the causative of an intransitive is used when the subject makes someone or something else perform the action.

3. Shortened Form (Casual):
In casual speech, causative verbs are sometimes shortened by replacing 〜せる with 〜す. This is most common with Group 1 (Godan) verbs (e.g., 行かせる becomes 行かす; 読ませる becomes 読ます). Note that Group 1 verbs ending in す (like 話す（はなす） or 探す（さがす）) generally cannot be shortened to 〜さす due to the awkward repetitive sound. While less common in standard Japanese, shortened forms for Group 2 (Ichidan) verbs (e.g., 食べさす) and irregular verbs (e.g., さす) also exist in very casual speech or specific regional dialects.

4. Nuance and Sociolinguistic Rules:
The bare causative form is strictly 'top-down' (used by superiors to subordinates, parents to children, etc.). It cannot be used to describe making or letting a superior do an action. Because this form can sound forceful, it is often combined with 〜てあげる or 〜てくれる to clearly express 'letting' someone do something as a favor. In formal requests, the pattern 〜させてください (please let me do) is very common. Additionally, combining the causative with receiving verbs like もらう (e.g., 〜させてもらえませんか) is a core, indispensable usage for politely asking for permission. Finally, to express being forced to do something from the victim's perspective, Japanese naturally uses the causative-passive form (使役受身, e.g., 〜させられる), as Japanese culture tends to avoid direct expressions of forcing.