12 a.m. or 12 p.m.?
Which sentences are correct?
- Noon is at 12 a.m.
- Noon is at 12 p.m.
- Midnight is at 12 a.m.
- Midnight is at 12 p.m.
The correct sentences are B and C.
Why?
Midnight is considered the beginning of the day, not the end of the day. A day begins in the morning and a.m. indicates morning, so midnight is 12 a.m.
The abbreviations a.m. and p.m. stand for the Latin terms ante meridiem (“before midday”) and post meridiem (“after midday”), respectively, with “midday” being noon. In Ancient Rome, time was measured by the Sun, and noon was the time when the Sun was highest in the sky. Before noon, the Sun rose. After noon, the Sun descended. That’s what the change from a.m. to p.m. designates, irrespective of the number 12, which signifies the same time. So even though 12 follows 11, at midday the time changes from a.m. to p.m. by definition of the terms.
Because midnight is considered the start of the day, it receives the “before midday,” or a.m., designation.
For practical purposes, simply remember that 12 on the clock is followed by a different abbreviation than follows the numbers 1–11 that precede it.
