the contrast between and is neutralized before and : . by convention, it is often assumed to be , though some analyze it as , the voiced counterpart to . the writing system preserves morphological distinctions, though spelling reform has eliminated historical distinctions except in cases where a mora is repeated once voiceless and once voiced, or where rendaku occurs in a compound word: , from . some dialects retain the distinctions between and and between and , while others retain only and but not and , or merge all four (see yotsugana).