In addition, there are some scholars who differ on opinions about the categories of Jodai (until the Nara period), Chuko (in and around the Heian period), medieval, early modern, modern, and present, and in some cases Chuko is not used at all.
また、上代・中古・中世・近世・近現代という区分けには研究者によって異論もあり、中古を設定しない場合もある。