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.