[thaumasiotes]

> The "f" pronunciation has been retained only before "u", like in Fuji.

Well, there is a convention that syllables starting with h- are spelled with f- (in foreign transcription) if the following vowel is -u. There's not much difference in the pronunciation itself; maybe there was more of one when the spelling convention was set.

[adrian_b]

At least in the recent past and probably also today in some Japanese dialects, the "f" pronunciation must have been retained before "u".

For example, in some Okinawan dialects the "f" pronunciation has been retained before all vowels.

Because of this, after Okinawa was occupied by Japan in the last quarter of the 19th century, the Japanese used "fu" before vowels, to transcribe the Okinawan pronunciation. For instance, the Okinawan syllable "ha" (pronounced "fa") was transcribed by the Japanese as "fua", because writing it like "ha" would have resulted in a too different pronunciation.

So at least by that time "fu" must have been still perceived as clearly different from "ha", "hi", "he" and "ho".

[thaumasiotes]

> At least in the recent past and probably also today in some Japanese dialects, the "f" pronunciation must have been retained before "u".

I wasn't disputing that as to the recent past.

I searched up some Japanese-language videos on youtube as a followup, and I can report:

A noticeable "f" is present before "u" in many cases. (I found it in the words "tofu" and "daifuku", plus the obvious English loanwords "soft", "firm", and "waffuru". My best guess as to the vowel following "f" is "u" for "soft" and "a" for "firm".)

But, not consistently. You don't have to pronounce the syllable that way. (Observed also in "tofu" and "daifuku".)

The nature of my low-effort search precludes any statements about dialectal variation. I wouldn't want to claim that the syllable onsets are "clearly different" to modern speakers today. But (1) the option to have an "f" is still present in -u syllables, and (2) the existence of common loanwords where the foreign sound is recognized is, if anything, going to serve to strengthen awareness of the hypothetical difference.

[adrian_b]

I agree with you.

I was explaining the historical pronunciation, because without knowing it, for the English speakers there are many puzzling things related to the syllables starting with "h", e.g. why "hashi" is voiced to "-bashi", why hiragana "huji" is transcribed to Latin "Fuji", why the particle "wa" is written "ha" in hiragana, why the capital city of Okinawa, which is now written "Naha" (because now the traditional Okinawan pronunciation does not matter any more) can be found in older texts written as "Nafua", why "Yawara" (the original native name of what is now called "jiu-jitsu", through translation into Sino-Japanese) was written in hiragana as "yahara" in the old books, and so on.

As you have mentioned, modern Japanese frequently uses "fu" before vowels or in final position, in transcribing the words borrowed from English or other languages, to mark the consonant "f", which otherwise does not exist in Japanese, and in these borrowed words it is more likely to be pronounced as English "f".