Why 原因 Is げんいん, Not げいいん: Japanese Sounds That Fool Your Ears
The word 原因 (cause) is read げ-ん-い-ん. But ask a class to write it down and half will put げいいん. What is striking is that even native speakers slip on words like this. Here is why your ears get fooled, and how to fix it.
The Trap
原因 has four beats (mora): げ・ん・い・ん. The middle is ん followed immediately by い. In fast speech, that ん + い runs together and starts to sound like a long え-ish vowel, so the ear hears げいいん, and that is what people write.
It is the same family of mistake as mishearing where a word breaks. Once you know the pattern, you can catch it every time.
Why ん + Vowel Blurs
The ん (moraic nasal) changes its sound depending on what follows it. Before a vowel, it is pronounced as a nasalized sound with no clear consonant edge, so the boundary between ん and the next vowel becomes soft and hard to locate.
The fix is to remember that ん is always its own full beat. Count it deliberately: げ (1) ん (2) い (3) ん (4). If you give ん its beat, you will never collapse it into the next vowel.
Words Everyone Gets Wrong
Why Typing Catches It, Speaking Doesn't
Speech optimizes for ease of articulation, so a native speaker's mouth will happily blur げんいん toward げいいん because it is a smoother motion, and listeners fill in the gap from context anyway. Typing removes that shortcut entirely: an IME has no context to fill in, so it converts exactly what you told it, mora by mora.
This is why the same person can say a word slightly wrong for years without noticing, then suddenly discover the mistake the first time they try to type it. The keyboard is a stricter test than the ear.
Test Yourself
Before reading on, say these three words slowly, counting the beats on your fingers: 訓練 (くんれん, training), 反応 (はんのう, reaction), 婚姻 (こんいん, marriage). Each one has a ん sitting directly before a vowel or a nasal-adjacent sound, the same structure that trips people up on 原因.
If any of them came out shorter than their real mora count, that is exactly the blur this article is about, just with a different word. The fix is identical: give ん its own beat every time, regardless of which word it appears in.
Let Typing Check You
The Japanese IME is a free spell-checker for exactly this. Type genin and 原因 appears. Type geiin and it will not convert correctly. If your reading does not turn into the kanji you expect, your reading is wrong.
Make this a habit: whenever a word with ん + vowel won’t convert, slow down and find the ん you dropped.
Teacher’s Note
Don’t feel bad about these. 雰囲気 (ふんいき) is mispronounced as ふいんき so often that nearly everyone has done it. The cure is the same for all of them: treat ん as a real, countable beat. Mora counting fixes pronunciation, spelling, and listening all at once.
Learn words by their sound, not just their kanji
Nihongo Pass pairs every word with native audio and readings, so ん + vowel words like 原因 and 雰囲気 stick correctly from day one.