As is also shown in "Manyoshu," where expressions like 'reading days' or 'reading months' are used to mean measuring time (or counting days), historically speaking the cycles of the moon phase and its motion have provided a basis for calendars; and, as considered worldwide, the lunar calendar has an older origin than the solar one.
「読む」は、万葉集にも「月日を読みて」「月読めば」など時間（日月）を数える意味で使われている例があり、また暦の歴史を見ると、月の満ち欠けや運行が暦の基準として用いられており、世界的に太陰暦が太陽暦に先行して発生したのである。