JLPT N1: べからざる (must not)

Perhaps some of you remember the following lesson: [NDL #354] - JLPT N1: べく.

In that lesson, I briefly mentioned how ～べきだ (N3 grammar) means something like "should." And we saw how べく (N1 grammar) means something like "thinking to" or "for the purpose of."

Well, べからざる is pretty much the opposite of those, as it means something along the lines of "must not." This makes sense because the verb ending ～ざる denotes negation--that is, it means "not."

Examples are the best teachers:

親からの愛は子供の健やかな成長には欠くべからざるものだ。
おや　から　の　あい　は　こども　の　すこやかな　せいちょう　に　は　かく　べからざる　もの　だ。
The love of a parent is vital to the healthy growth of a child.
Literally: "parent + from + の + love + は + child + の + healthy + growth + には + lack / be lacking + べからざる + thing + だ."

So the verb 欠く (かく) means "to lack," "to be lacking," "to be short of."

We add べからざる to the end of it, and it gives us "must not be lacking."

In the translation, "must not be lacking" was changed to "is vital to."

欠く（to be lacking）
欠くべからざる（must not be lacking）

Here's the construction:

V る ＋ べからざる

In this lesson, we'll use these verbs and verb phrases:

欠く（かく // to lack; to be lacking）
軽視する（けいしする // to think lightly of; to disregard）
許す（ゆるす // to allow; to forgive）
知る（しる // to know）

All we have to do is attach べからざる to the dictionary form:

欠くべからざる（must not lack）
軽視するべからざる（must not take lightly）
許すべからざる（must not allow/forgive）
知るべからざる（must not know）

Note that べからざる will always be followed by a noun.

In this lesson, we see it followed by:

もの（thing）
こと（thing）
問題（もんだい // problem）
行為（こうい // behavior; actions）

Specifically, we have:

欠くべからざるもの（thing that must not be lacking）
軽視するべからざる問題（problem that must not be taken lightly）
許すべからざる行為（behavior that must not be allowed）
知るべからざること（thing that must not be known）

Perhaps, with that, you have prepared yourself enough to take on the remaining example sentences...

日本の少子高齢化は軽視するべからざる問題になっている。
にほん　の　しょうし　こうれいか　は　けいし　する　べからざる　もんだい　に　なっている。
Japan’s declining birthrate and aging population are becoming a problem that must not be taken lightly.
Literally: "Japan + の + declining birthrate + aging population + は + taking lightly + do + べからざる + problem + is becoming."

I highly recommend memorizing these terms if you ever want to have high-level conversations about Japanese society. They are used all the time:

少子化（しょうしか // declining birthrate）
高齢化（こうれいか // aging population）
少子高齢化（しょうしこうれいか // declining birthrate and aging population）

We can also add 社会 (しゃかい // society) to the end of them. This is useful because Japan is a society with a declining birthrate and an aging population:

少子化社会（しょうしかしゃかい // society with a declining birthrate）
高齢化社会（こうれいかしゃかい // society with an aging population）
少子高齢化社会（しょうしこうれいかしゃかい // society with a declining birthrate and aging population）

This is seen as a huge problem in Japan because they're about to have too many old people and not enough young people to support them. Personally, I wish that all countries had this problem because I'm terrified that the exploding human population is going to result in mankind's ultimate destruction... but using that argument to posit that a decreasing population is a good thing doesn't seem to work too well in Japan (I always get shut down when I try to make this point T_T).

家庭内暴力は許すべからざる行為である。
かていない　ぼうりょく　は　ゆるす　べからざる　こうい　である。
Domestic violence is a behavior that must not be allowed.
Literally: "in the home + violence + は + allow + べからざる + behavior + である (=is)."

どうやら私は知るべからざることを知ってしまったようだ。
どうやら　わたし　は　しる　べからざる　こと　を　しって　しまった　ようだ。
It seems that I’ve somehow learned something that I should not know about.
Literally: "somehow + I + は + know + べからざる + こと + を + learned of (=know and + did [completely]) + seems + だ."

Normally I'd say to go out try to use the grammar point in everyday life, but I don't think you need to be using this one. You might come across it every now and then, in which case you'll want to understand it. But I personally never use it.

In other JLPT lessons (e.g. ～してはいけない), we'll see more common/useful equivalents.