Can i use the っ to replace the ん in こんにちは, it would still be konnichiwa right?
If i can't then please explain to me why.
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2019-10-14T06:31:01.320
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2019-10-14T09:17:21.810
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question
hiragana kana-usage gemination
っ(sokuon) usage
This is why you shouldn't rely on romanization while learning Japanese
phonology. Looking through the lens of romaji, っ and ん may certainly seem to
do more or less the same thing: きっさ _kissa_ , はっぱ _happa_ , あんな _anna_ , and
ぐんま _gumma_ (the last one may vary according to the practice). This is because
romaji aims to make Japanese pronunciation friendly to those who read Roman
alphabet, and not to reflect its internal mechanism.

The truth is, っ and ん represent their own, what is called "moraic phoneme",
respectively.

  * っ: moraic obstruent //Q//*
  * ん: moraic nasal //N//*

Confusingly, they don't have single fixed sound values on their own, but have
different realization depending on what comes after (or lack thereof), as in
below (or [see this answer for deeper
analyses](https://japanese.stackexchange.com/a/57122/7810)):

> 新 しん _shin_ //ɕiN// [[ɕĩ ~ ɕĩɴ]]  
>  新米 しんまい _shimmai_ //ɕiNmai// [[ɕĩmmɐi]]  
>  新年 しんねん _shinnen_ //ɕiNneN// [[ɕĩnnẽ(ɴ)]]  
>  新型 しんがた _shingata_ ** //ɕiNgata// [[ɕĩŋŋɐ(~ ɡɐ ~ ɣɐ)tɐ]]

The cheat sheet is that when you see _m_ or _n_ doubled in romaji, it
represents ん + [next consonant], and everything else doubled is っ + [next
consonant]. So _konnichiwa_ never stands for こっにちは. こんにちは can never be spelled
こっにちは. And こっにちは does not exist as a word.

Then is こっにちは unpronounceable? Not necessarily. Such kind of combination [does
exist in colloquial Japanese and is actively
used](https://japanese.stackexchange.com/a/20995/7810). But I doubt if there
is any romanization method that can transcribe it, because they're never
expected to appear as long as you speak in "good grammar", so far.

Incidentally, I can probably show their contrast if I can assume you speak
Vietnamese. [A Vietnamese phrasebook for Japanese tourists by Vietnam
Airlines](https://www.meetsvietnam.com/conversation_book/conversation_book.pdf)
gives the pronunciation ヴィエ **ッ** ナーム for _Việt Nam_ , while チュエンヴィエ **ン** for
_chuyên viên_. Thus I can say that replacing こんにちは with こっにちは would be as
different as that of _viên + nam_ with _viêt + nam_.

* * *

*: In academic literature, they are likely printed in small caps; if your environment supports them: //ꞯ// and //ɴ//  
**: Note that even romaji does not write it "phonetically" like * _shinggata_
, because it is natural in European languages that an _n_ followed by _g_
changes into _ng_ sound.
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