What does らん in 「強からん事を祈る」 mean?

Question

I came across this sentence while reading Osamu Dazai's Ningen Shikkaku. The sentence is pretty long, so I have only included the relevant part.

あまりに人間を恐怖している人たちは、かえって、もっともっと、おそろしい妖怪を確実にこの眼で見たいと願望するに到る心理、神経質な、ものにおびえ易い人ほど、暴風雨の更に強からん事を祈る心理、ああ、この一群の画家たちは...

When I searched it online, I came across this article on Chiebukuro which says:

「推量」になりますが、ヨーロッパの言語でいう接続法などに近い用法です。

「ん」 in 「らん」 becomes some kind of guess or conjecture here. But what I do not understand is, what kind of form is 「強から」.

「強か」 is a な-adjective but I am confused as to what the that bold part in the sentence means and how it fits in the overall context of the larger sentence.

Complete sentence for reference:

あまりに人間を恐怖している人たちは、かえって、もっともっと、おそろしい妖怪を確実にこの眼で見たいと願望するに到る心理、神経質な、ものにおびえ易い人ほど、暴風雨の更に強からん事を祈る心理、ああ、この一群の画家たちは、人間という化け物に傷めつけられ、おびやかされた揚句の果、ついに幻影を信じ、白昼の自然の中に、ありありと妖怪を見たのだ、しかも彼等は、それを道化などでごまかさず、見えたままの表現に努力したのだ、竹一の言うように、敢然と「お化けの絵」をかいてしまったのだ、ここに将来の自分の、仲間がいる、と自分は、涙が出たほどに興奮し、 「僕も画くよ。お化けの絵を画くよ。地獄の馬を、画くよ」

Answer 1

Adding onto Ringil's post.

The crux of the question

what I do not understand is, what kind of form is 「強から」.

To understand this, we need to look more deeply into how い adjectives can be inflected or conjugated.

Some background: inflected forms of い adjectives

As Ringil notes, this derives from base adjective 強【つよ】し (classical terminal [sentence-ending] form), modern 強【つよ】い.

In Classical Japanese, the い adjectives had two inflection patterns. One of these evolved into the modern one you're probably familiar with, and is generally called the 本【ほん】活用【かつよう】 or "main" conjugation.

The "main" conjugation pattern for Classical い adjectives: ク活用【かつよう】

Another name for this pattern is ク活用【かつよう】, so-named for the adverbial form ending in く. Japanese grammars distinguish this from the シク活用【かつよう】, used for those い adjectives that end in しい, like 美【うつく】しい or 素晴【すば】らしい. (We won't go into the シク活用 pattern here.)

• 強し - the 終止形【しゅうしけい】 or terminal form, used to end a sentence or clause
• 強き - the 連体形【れんたいけい】 or attributive form, used to modify a noun
  → As Classical evolved into modern, the attributive lost the //-k-// to end in just //-i//, and then the attributive replaced the terminal.
• 強く - the 連用形【れんようけい】 or adverbial form, used to modify a verb or clause, or otherwise indicate the manner
• School grammars also list the 未然形【みぜんけい】 or irrealis ("hasn't happened yet, or hasn't completed yet") form, mostly used for the negative. For い adjectives, this is the same as the adverbial.
• 強けれ - the 已然形【いぜんけい】 or realis ("has happened already") form, most commonly used in modern Japanese for the conditional ば
• There isn't any 命令形【めいれいけい】 or imperative form for い adjectives.

The "other" conjugation pattern for Classical い adjectives: カリ活用【かつよう】

This other inflection pattern has mostly disappeared from the modern language, outside of some set phrases. This pattern is called the カリ活用【かつよう】 or "kari" conjugation.

• There isn't any 終止形【しゅうしけい】 or terminal form
• 強かる - the 連体形【れんたいけい】 or attributive form, used to modify a noun
• 強かり - the 連用形【れんようけい】 or adverbial form, used to modify a verb or clause, or otherwise indicate the manner
• 強から - the 未然形【みぜんけい】 or irrealis ("hasn't happened yet, or hasn't completed yet") form, mostly used with the negative and certain other auxiliaries
• There isn't any 已然形【いぜんけい】 or realis form for the kari pattern.
• 強かれ - the 命令形【めいれいけい】 or imperative form

This kari conjugation is actually a contraction, formed from the regular く adverbial ending + the various inflections of あり (the Classical "to be" verb, as found in modern あります). This is also where we get the modern "past tense" for い adjectives -- forms like 強かった are contractions of 強く + あった.

Your problem word: 強からん

As we see above in the kari conjugation pattern, 強から is the 未然形【みぜんけい】 or irrealis stem used with the negative and certain auxiliaries. This 強から is essentially 強く + あら, where あら in turn is the 未然形【みぜんけい】 or irrealis stem of あり (modern ある).

The ん on the end is a contraction, in this case, of the suppositional / volitional auxliary む. This attaches to the 未然形. Over time, this //-amu// ending became the modern suppositional / volitional ending //-oː//.

(I've delved into these historical sound changes in む in a different post; please read that for more detail.)

So 強からん = 強からむ = 強く + あらむ = (in modern Japanese) 強いだろう.

Side note: 強か

You mention:

「強か」 is a な-adjective

In that case, the reading is したたか. While a valid reading, that form doesn't fit the grammar of the sentence, since then we'd have 強【したた】からん, and there is no らん or らむ ending that attaches straight onto the root of な adjectives.

Answer 2

強し{つよし} - base adjective

強から - 未然形

強からむ = 未然形 + auxiliary む

強からん = 未然形 + auxiliary む with sound change

As the thing in Chiebukuro says, む is usually used to express volitional/speculation. I think in this case, it doesn't add too much to the meaning and that 暴風雨の更に強からん事を祈る means to pray for stronger/more dangerous storms.