Plain Verb followed by がよい

Question

Recently I am reading 走れメロス, and there is a sentence pattern that I am not familiar with (Group 2). Compare the following sentence groups:

Group 1

訪ねて行くのが楽しみである。

疑うのが、正当の心構えなのだと、わしに教えてくれたのは、おまえたちだ。

Group 2

自惚れているがよい。

その身代りを呼ぶがよい。

勝手にするがよい。

There is a nominalizer の before the verb in Group 1's sentences, whereas it doesn't in Group 2's. I am aware that it is always plain verb followed by "がよい" in the text, but what does "plain-verb がよい"exactly mean? Does the meaning remain natural or the same if a nominalizer (say, の) is added? (Though I speculate "plain-verb がよい" approximates its volitional counterpart, but I am not sure).

Furthermore, can "plain-verb が" followed by other kinds of 述語 rather than "良い"? Is "plain-verb がよい" still used in modern Japanese? If so, would you use it personally in everyday life, hear it from other people's utterance, or the sentence pattern is more likely to be used in a play script spoken by actors?

It is my first time to see this sentence structure, so I have many doubts. Would you tell me as much as you know about this sentence pattern?

Answer 1

In archaic Japanese, there was no such thing as a nominalizer. Instead, the 連体形 (or attributive form, noun-modifying form) of a verb was used to nominalize a verb. We can still see an attributive form used as a noun in proverbs and idioms, for example 逃げるが勝ち ("Running is winning") and 聞くは一時の恥 ("Asking is a one-time shame").

～するがよい uses the same grammar. This ～がよい is a part of role language used almost exclusively in fiction by archaic demon, samurai, noble people, etc. It sounds fairly old-fashioned and pompous. The negative counterpart is ～するでない (e.g., 呼ぶでない = Call not).