Almost all civilizations have based their calendars on either the lunar month or the solar year, despite the inherent difficulty that the year is not made up of an exact number of lunar months.

• 尽管存在着年并非由准确的太阴月数组成这一内在困难，但是几乎所有文明社会都是将他们的历法建立在太阴月或太阳年基础之上的。