Understanding AD/BC and CE/BCE: Historical Dating Systems Explained

The abbreviations AD and BC (or their secular equivalents CE/BCE) are the global standard for labeling years. "AC" is not a standard abbreviation in English-language historiography; it appears to be a confusion with the Latin Anno Domini (AD) or the Romance language equivalents (e.g., Spanish a.C. = antes de Cristo, Italian a.C. = avanti Cristo).

Standard English Conventions

• AD (Anno Domini) = "In the Year of the Lord." Years after the traditionally calculated birth of Jesus Christ. Written before the year: AD 2024.
• BC (Before Christ) = Years before that epoch. Written after the year: 500 BC.
• No Year Zero: 1 BC is immediately followed by AD 1.

Secular/Academic Alternatives

• CE (Common Era) = equivalent to AD. 2024 CE.
• BCE (Before Common Era) = equivalent to BC. 500 BCE.
• Preferred in interfaith, scientific, and international contexts. Identical numbering.

Other "AC" Usages

In specific contexts, AC may stand for:

• Ante Christum (Latin for "Before Christ") – rare, mostly in older European texts.
• After Christ – informal, non-standard English usage.
• Anno Conditae (or Ab Urbe Condita / AUC) = "From the Founding of the City (Rome)" – 753 BC = AUC 1. Used in classical studies.
• Alternating Current – electrical engineering.

Practical Guidance

• Use AD/BC or CE/BCE consistently.
• In English writing, avoid "AC" for years—it will confuse readers.
• For ancient dates, specify the calendar (Julian vs. Gregorian) if precision matters.

The dating system originated with Dionysius Exiguus (6th century monk) and was popularized by Bede. Its global adoption reflects historical contingency—not theological consensus. CE/BCE retains the same epoch while acknowledging diverse users.