べからずDo not, Must not, Should not, Cannot (べからざる)

べからず, and べからざる are two formal expressions used to convey the meaning of 'must not (A)', or 'ought not to (A)'. It is a combination of the helper-conjugation form of the auxiliary verb べし, べから, and the classical auxiliary verb ず 'not'. ざる itself is just the helper-conjugation form of ず, meaning that the nuance remains exactly the same. In this way, we can see that the literal meaning of 'ought not (A)' exhibits some sort of moral or logical obligation, as is true for all uses of べき derived patterns.

べからず and べからざる will be seen following verbs in their dictionary forms. べからざる will be followed by a noun, indicating that the noun is being modified by the phrase.

• ことわざ：「初心(しょしん)忘(わす)れるべからず。」

  Proverb: 'Do not forget beginner's humility.'
• この施設内(しせつない)ではスケートボードなどのことをするべからず。

  You must not skateboard or anything similar in this facility.
• 配達員(はいたついん)を装(よそお)って玄関(げんかん)のドアを開(あ)けさせるのは、許(ゆる)すべからざる行為(こうい)だ。

  Making someone open the door, by pretending to be a delivery person is an act that is not to be forgiven.
• 吸(す)うべからざる場所(ばしょ)でタバコを吸(す)っているのを見(み)られたら、１０００(せん)円(えん)払(はら)うことになります。

  If you are seen smoking in an area where you must not smoke, you will end up having to pay 1000 yen.

In modern Japanese, the meanings of both of these grammar patterns have shifted slightly from 'obligation', to simply having a strong nuance of 'don't (A)'. In addition to this, they will almost only ever be used on signs or notices.

Caution

The べからざる form that combines with nouns is usually only seen in a few set variations. These are 許(ゆる)すべからざる 'cannot be forgiven', ありうべからざる 'must not exist' (impossible), and 欠(か)くべからざる 'must not be without'.