of kana ha hi fu he ho are used to represent, in some words, the sounds wa, i, u, e, o, respectively. Precedence is given to grammar over pronunciation. For example, the verb warau (to laugh), is written warafu, and in accordance with Japanese grammar rules, waraō, the volitional form of warau, is written warahau. The kana du and di, which are mostly only used in rendaku in modern kana usage, are more common. Modern kana usage replaces them with the identically-pronounced zu and ji in most cases. For example, ajisai (hydrangea) is written adisawi. Most of the historical kana usage has been found to accurately represent certain aspects of the way words sounded during the Heian period. As the spoken language has continued to develop, some orthography looks odd to the modern eye. As these peculiarities follow fairly regular patterns, they are not difficult to learn. However, some of the historical kana usages are etymologically mistakes. For example, aruiwa (or) might be found written incorrectly as: *aruhiwa or *aruwiwa mochiwiru (use) might be found written incorrectly as: *mochihiru tsukue (desk, table) might be found written incorrectly as: *tsukuwe Those familiar with Japanese writing may notice that most of the differences apply to words which are usually written in Kanji anyway, and so would require no changes to switch from one Kana system to another (unless furigana are employed). In particular, yōon sounds occur almost exclusively in the Chinese-derived readings that are usually only seen in Kanji compounds (although not entirely; kyō "today," written kefu in the old system, is a native Japanese word), and therefore do not look any different (without furigana). The relative lack of difference in appearance in practice between the two systems was a major reason the spelling reform succeeded, and also why the three grammatical particles o, e, wa continue to be written as wo, he, and ha instead of o, e, and wa; many felt that changing these exceedingly common spellings would unnecessarily confuse readers. It is also for this reason that many character dictionaries continue to include the historical spellings, since they are relevant there. Some forms of unusual kana usage are not, in fact, historical kana usage. For example, writing dojō (loach, a sardine-like fish) in the form dozeu is not historical kana usage (which was dodiyau), but a kind of slang writing originating in the Edo period. Examples Here are some