公元
The English phrase "common Era" appears at least as early as 1708, and in a 1715 book on astronomy it is used interchangeably with "Christian Era" and "Vulgar Era". A 1759 history book uses "common æra" in a generic sense, to refer to the common era of the Jews. The first use found so far of the phrase "before the common era" is in a 1770 work that also uses "common era" and "vulgar era" as synonyms, in a translation of a book originally written in German. The 1797 edition of the Encyclopædia Britannica uses the terms "vulgar era" and "common era" synonymously. In 1835, in his book "Living Oracles", Alexander Campbell, wrote: "The vulgar Era, or Anno Domini; the fourth year of Jesus Christ, the first of which was but eight days", and also refers to the "common era" as a synonym for "vulgar era" with "the fact that our Lord was born on the 4th year before the vulgar era, called Anno Domini, thus making (for example) the 42d year from his birth to correspond with the 38th of the common era..." The "Catholic Encyclopedia" (1909) in at least one article reports all three terms (Christian, Vulgar, Common Era) being commonly understood by the early 20th century.