べからず・
べからず gives a forceful, literary command not to do something. べからざる appears before a noun and presents an act, error, or situation as unacceptable or impermissible.
Choosing between the two forms
べからず ends the instruction itself: it tells the reader that an action must not be done. べからざる instead carries that judgment into a following noun phrase, often producing English such as “an unforgivable act,” “an unacceptable error,” or “something that must not be overlooked.”
Warnings and condemnation
The sentence-final form is naturally terse, while the noun-modifying form is common in solemn criticism.
How it sounds today
Although you can build this pattern with many verbs, that does not make it a normal everyday prohibition. For ordinary modern rules, instructions, and conversation, speakers generally choose a modern construction. Use this pattern when the severe, maxim-like, or old-fashioned tone is itself appropriate.
A maxim-like use
権力は私益のために用いるべからず。
Power must not be used for private gain.
AnalyzeThe form makes this sound like a solemn principle rather than a casual opinion.
More examples
この門より内に入るべからず。
Do not enter beyond this gate.
Analyze公の記録を私意で改めるべからず。
Public records must not be altered for personal reasons.
Analyzeいかなる理由があろうとも、人の尊厳を傷つけるべからず。
Whatever the reason, one must not violate human dignity.
Analyze研究者として、データを都合よく操作すべからず。
A researcher must not manipulate data for convenience.
Analyzeこれは民主社会において許すべからざる暴挙である。
This is an outrage that cannot be tolerated in a democratic society.
Analyzeその発言は、指導者として口にすべからざるものであった。
That was something a leader should never have said.
Analyze決して見過ごすべからざる兆候だ。
It is a warning sign that must not be overlooked.
Analyze