A regulation in the ritsuryo codes ('Gisei-ryo,' or the regulation of ceremonies code) regarding the title to be used for the Tenno states that the Emperor should be called 'Sumemimanomikoto,' 'Sumeramikoto,' or another such title in accordance with the customs of that time; this was despite the fact that there were already seven ways of addressing the Emperor—'Tenshi' at ceremonies, 'Tenno' in Shosho (imperial edicts or decrees), 'Kotei' in relations with China (domestic and diplomatic), 'Heika' when addressed by vassals in close proximity, 'Daijo-Tenno' when retired, 'Joyo' when going out, and 'Shaga' when traveling—because these names are only used in writing ('Tenshi' attending ceremonies in particular were addressed as 'Sumemimanomikoto').
天皇という呼称は律令制（「儀制令」）に規定があり、祭祀においては「天子」、詔書には「天皇」、華夷においては（国内外にむけては）「皇帝」、臣下がすぐそばから呼びかける時には「陛下」、皇太子など後継者に譲位した場合は「太上天皇（だいじょうてんのう）」、外出時には「乗輿」、行幸時には「車駕」という7つの呼び方が定められているがこれらはあくまで書記（表記）に用いられるもので、どう書いてあっても読みは風俗（当時の習慣）に従って「すめみまのみこと」や「すめらみこと」等と称するとある（特に祭祀における「天子」は「すめみまのみこと」と読んだ）。