Remembering when to use [原]{げん} and when to use [源]{げん}?


The kanji 原 and 源 seem to often have not only an identical pronunciation, but
also a very similar meaning, and I'm having a lot of trouble remembering the
spellings of several words:

Using 原:

  * [[原]{げん}[因]{いん}](http://jisho.org/word/%E5%8E%9F%E5%9B%A0) - cause, source, origin
  * [[原]{げん}[始]{し}[的]{てき}](http://jisho.org/word/%E5%8E%9F%E5%A7%8B%E7%9A%84) - primitive; original

Using 源:

  * [[起]{き}[源]{げん}](http://jisho.org/word/%E8%B5%B7%E6%BA%90) - origin; beginning; rise
  * [[水]{すい}[源]{げん}](http://jisho.org/word/%E6%B0%B4%E6%BA%90) - fountainhead, source of a river

I'm wondering if there's some shade of meaning that I am missing between these
two characters, or maybe if there's some Japanese equivalent to the "i before
e except after c" rule that would help me remember which is which. For the
most part, it does not seem that the words containing 原 have anything more to
do with meadows than the words containing 源.




Putting etymology aside, in modern Japanese...

源 means _resource_. When one can draw something useful from it, always use ○源.
Similarly, a place from which something is (radially) emitted is described
using 源.

  * 水源、電源、光源、熱源、財源、音源、動力源、エネルギー源、タンパク源
  * 震源、発生源、汚染源、ノイズ源

原 means _cause_. When it's the cause for something, use 原. (incidentally
English uses a similar-looking suffix `-gen`)

  * 原因、病原体 (pathogen)、アレルギー原 (allergen)

原 also means _primitive_ or _fundamental_ :

  * 原始、原初、原子、原理、原則、原色

原 also means _atomic/nuclear_ :

  * 原発 (short for 原子力発電所)、原爆 (short for 原子爆弾)

Unfortunately, these are still many difficult cases, especially when the word
translates to "origin(al)" or "source". But you can use 原 and 源
interchangeably in some cases.

  * 原型、原作、原料
  * 源泉
  * 起源 / 起原
  * 語源 / 語原
  * 根源 / 根元 / 根原




Putting etymology aside, in modern Japanese...

源 means _resource_. When one can draw something useful from it, always use ○源.
Similarly, a place from which something is (radially) emitted is described
using 源.

  * 水源、電源、光源、熱源、財源、音源、動力源、エネルギー源、タンパク源
  * 震源、発生源、汚染源、ノイズ源

原 means _cause_. When it's the cause for something, use 原. (incidentally
English uses a similar-looking suffix `-gen`)

  * 原因、病原体 (pathogen)、アレルギー原 (allergen)

原 also means _primitive_ or _fundamental_ :

  * 原始、原初、原子、原理、原則、原色

原 also means _atomic/nuclear_ :

  * 原発 (short for 原子力発電所)、原爆 (short for 原子爆弾)

Unfortunately, these are still many difficult cases, especially when the word
translates to "origin(al)" or "source". But you can use 原 and 源
interchangeably in some cases.

  * 原型、原作、原料
  * 源泉
  * 起源 / 起原
  * 語源 / 語原
  * 根源 / 根元 / 根原

