When should I replace kanji with hiragana?

Question

When should I write 海山 and when should I write うみやま?

Answer 1

Well, it's always safe to use the hiragana. You could technically write Japanese entirely in kana, although it would become very difficult to read and lack the context clues provided by kanji.

If 海山 is someone's (family) name, first make sure it is really pronounced as うみやま because it could have some other pronunciation. Secondly, depending on the context for which you're writing the name, you have several different options.

If you're using 海山 to just mean "the sea and mountains" (or the phrase 海山の恩), you can, and probably should use kanji.

So what's the rationale for using replacing kanji with hiragana? Well, if you don't know how to write the kanji, you can always fall back to hiragana as I mentioned. Another rationale would be writing something like a children's book. Since young children may not know kanji, or how to read a certain kanji, the author may use hiragana (although I believe 海 and 山 are likely taught at a young age).

And although you didn't ask the inverse question, I'll answer it anyway. What's the rationale for using kanji instead of all kana? As I said, ease of reading. Once you start learning kanji, reading anything written in all kana can be "difficult"; not that it's hard, but certainly can take longer. Kanji also gives context. Japanese has many homonyms, so seeing something written in kanji can give you a reasonable, if not exact understanding of what it means. For example, if I write the word いし, you don't know if I mean "rock" (石), "doctor" (医師), "will/volition" (意志), or any of the many other words with that pronunciation.

Answer 2

Hiragana is a script, which in normal Japanese texts is used alongside with kanji and katakana. Hiragana is usually used for grammatical functions (e.g., particles, verb inflections, etc.) and for words for which there doesn't exist kanji, or for words, whose kanji are non-standard. 海山 would usually be written in kanji. However, 海山 could in principle also be read かいさん (or かいざん, see dainichi's comment below), which may be a reason for writing it with furigana (like so [海山]{うみやま}) or with hiragana alone, for example in books for primary school kids. Does this answer your question?