What it means
べからず expresses a strong prohibition: “must not” or “should not.” It follows a verb in the dictionary form and is mainly used in formal written language, official rules, warnings, regulations, and solemn statements. Its tone is forceful and somewhat archaic or literary, so it is uncommon in ordinary conversation.
Usage note
べからず is not a polite conversational form. In everyday speech, use 〜てはいけない, while 〜てはならない is a more contemporary formal alternative for strict rules or prohibitions.
Example sentences
図書館の資料を、館長の許可なく持ち出すべからず。
Library materials must not be taken out without the director's permission.
作業中の機械に手を触れるべからず。
Hands must not touch the machinery while it is operating.
災害時の避難経路を妨げるべからず。
Do not obstruct evacuation routes during a disaster.