Hi,
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Japanese Writing and Pronunciation
In writing, a Japanese employs Chinese characters and kana together. A Chinese character has its individual meaning as well as the sounds, and it is employed for nouns, verbs, adjectives and such "solid" words. A kana represents merely a syllable sound and it has no meaning of its own. It is employed for endings, post-positions and such parts of less import. There are forty-eight letters in kana while there are a limitless number of Chinese characters.
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It is not impossible to write everything in kana, but (1.) that will betray the lack of education on the part of the writer. Indeed, the original meaning of the word kana is substitute letter, and the Chinese characters are considered real letters (hon-ji). (2.) Although the Chinese characters are difficult to learn, once they are learned and mastered, they make a most rapid reading possible, because they convey the meaning directly to the eyes without resorting to the "sound".
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p. 169, Japanese in Thirty Hours, Eiichi Kiyooka
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