なさい

なさい is a mild command form used to tell someone to do something. It is formed by attaching なさい to the verb stem (the masu-stem). While it is softer than the blunt imperative form (e.g. しろ), it still carries clear authority and is not used toward superiors or equals. It is most common by parents speaking to children, teachers to students, or in written instructions such as exam directions.

Formation

Remove ます from the polite form and add なさい:

• たべる食べる → 食べます → 食べ → 食べなさい
• よむ読む → 読みます → 読み → 読みなさい
• する → します → し → しなさい
• くる来る → 来ます（きます） → 来（き） → 来なさい（きなさい）

Tone and usage

なさい sits between 〜～てください (polite request) and the plain imperative (e.g. かけ書け、たべろ食べろ) in terms of directness. It sounds parental or instructional rather than rude, but it is clearly a command, not a request.

Shortened form

In casual speech, なさい is often shortened to ～な (with a falling intonation). This is very common among parents and close authority figures.

Be careful not to confuse this shortened な with the prohibitive な (e.g. いく行くな "don't go!"), which attaches to the dictionary form.