The Common Era is the period during which the current system of numbering years applies - the one under which the First world War began in 1914 and ended in 1918. It is abbreviated as CE. The period Before the Common Era is abbreviated as BCE. Some say that it stands for 'Christian Era'.
Counting starts from the supposed date of the birth of Jesus Christ (1 CE, although current scholarship suggests that c.4BCE, the date of the death of King Herod, who ruled at the time of the birth, is more likely). This explains the abbreviations A.D., or AD, and B.C., or BC, which were the norm before the very end of the twentieth century. 'B.C.' is the easier, being English: it stands for 'before Christ'. A.D. is from the Latin Anno Domini, which means 'in the year of the Lord'. (It dates back to early days of western Christianity, when the only Christian church was the Roman Catholic church, which used only Latin for all its business.)
- Students are recommended to use CE and BCE rather than AD and BC, as British society becomes less and less Christian and more and more multicultural. In the west, all other systems of counting year dates are minority.
- If you are studying history or literature, it may be appropriate to revert to the older system at times. A further complication can arise in dates before 1752, when the Julian Calendar, sometimes called OS or 'Old Style', was replaced by the Gregorian Calendar in use today.
- if you are studying (Christian)Theology, it may always be advisable to do so.
- If you are studying cultures which use other systems of dating, it may be sensible to include dates in that system - but always together with the equivalent in the BCE/CE numbers. For example, a student of Arab history might write the date of an event in Saudi Arabia which occurred in the year 2008 CE as (1429 AH, 2008 CE), using both the Islamic and Christian systems.
- Historical note: The system owes its origin to Dionysius Exiguus (died between 526 and 556), a Scythian monk who wanted to replace the Roman system of numbering years as the regnal years of the Emperors - particularly those who persecuted Christians. In 525 (CE), he began to number years from the birth of Jesus, which he marginally miscalculated as 753 a.u.c (= the supposed foundation of Rome). He called the years numbered from then Anni Domini Nostri Jesu Christi, 'the years of our Lord Jesus Christ'. The system was adopted by Bede in 731, and spread throughout Europe by 1422.