must not do; is not allowed to
Form: Verb in て-form + はいけない (plain) / はいけません (polite). Contracted in speech: 〜ちゃいけない for plain て, 〜じゃいけない after voiced て (飲んじゃいけない).
Meaning: direct prohibition — the speaker, a rule, or an authority is saying don't. Stronger than a request; used on signs, in classrooms, from parents.
Key forms: the て-form is the load-bearing piece — get that wrong and the whole pattern collapses. 食べる → 食べて + はいけない; 飲む → 飲んで + はいけない; する → して + はいけない; 来る → 来て + はいけない.
vs. 〜ないでください: please don't — polite request, softer, asks rather than forbids. vs. 〜てはならない: identical meaning, stiffer register (laws, contracts, formal writing). vs. 〜な (imperative negative): blunt one-word command, masculine — 行くな don't go.
Furigana is above every kanji; the pattern is already filled in.
ここで写真を撮ってはいけません。
You must not take photos here.
授業中に話してはいけない。
You must not talk during class.
この道は危ないから通ってはいけません。
This road is dangerous, so you must not go through it.