Causes and dependence with

因 means “the basis for something to come into being” or “a foundation”.

Etymology

This kanji is an pictographic character comprised of 囗 as an enclosure and 大 as a person, such as a person lying on a mat.

Causes

(Cause)

原因(げんいん) means the cause of a result or condition, often a problem, accident, or failure.

It combines 原 (origin) with 因 (cause) to show the originating cause.

Manga panel from カードキャプターさくら showing example of Cause of incidents in the pool with 原因.
カードキャプターさくら » Volume 1 » Page 112

After cheerleading practice, Sakura overhears her friends talking about incidents at the school pool, where Sakura and Chiharu were among those mysteriously pulled underwater.

千春(ちはる):
「きょう また プールで足(あし) 引(ひ)っぱられておぼれそうになったんだって」
“I heard that today, someone got dragged under the water at the pool and almost drowned again.”
奈緒子(なおこ):
「こわいねーーー」
“That's scary!”
千春(ちはる):
「先生(せんせい)が原因(げんいん)がわからないならプール閉鎖(へいさ)するしかないっていってたよ」
“The teacher said that if they can't figure out the cause, they'll have no choice but to close the pool.”
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(Cause of death)

死因(しいん) is the illness, injury, or event that caused someone to die. It is common in medical reports, police investigations, and legal records.

It combines 死 (death) with 因 (cause) to show the cause behind a death.

Manga panel from 名探偵コナン showing example of Determining the cause of death with 解剖.
名探偵コナン » Volume 16 » Page 25

Inspector Megure suggests the murder suspect committed suicide by drowning himself. The medical examiner disagrees.

監察医(かんさつい):
「ですが死因(しいん)は溺死(できし)ではありません…」
“However, drowning wasn't the cause of death...”
目暮(めぐれ):
「え?」
“What?”
監察医(かんさつい):
「解剖(かいぼう)してみないと断定(だんてい)できませんが… おそらく毒物(どくぶつ)を飲(の)んだあと池(いけ)に入(はい)ったものと…」
“I can't say for certain without an autopsy... but it's likely he took poison and then entered the pond...”
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