What Do AM And PM Actually Mean?

Most of us are familiar with the terms “am” and “pm” as references to the first half and the second half of the day, commonly known as morning and afternoon/evening. But have you ever wondered what those letters actually stand for?

A Look into Latin

Although Latin may be considered a dead language by some, its influence persists in various aspects of our lives, including how we denote time. “AM” originates from the Latin phrase ante meridiem, which translates to “before midday” in English. Conversely, “PM” is derived from post meridiem, meaning “after midday.”

If you’re inclined towards pedantry, you might be tempted to correct those who use “12 am” or “12 pm.” Technically, 12 pm cannot be “after midday” because it is midday. Royal Museums Greenwich recommends using “12 noon” or “12 midnight” to avoid confusion.

However, constant correction might earn you some raised eyebrows from your peers.

To Punctuate or Not to Punctuate

According to the Chicago Manual of Style, there are six accepted ways to abbreviate ante meridiem and post meridiem: all caps with periods, all caps without periods, small caps with periods, small caps without periods, lowercase with periods, and lowercase without periods.

Traditionally, the use of capital letters with periods was favored in formal style guides like Chicago. While this convention may still persist in some academic or publishing contexts, nowadays, any consistent method of abbreviation is generally acceptable.

The Less Confusing Alternative

If you’re concerned about mistakenly showing up at the airport at 4 pm instead of 4 am (a mistake worth avoiding), you might consider switching to the 24-hour system.

Although your friends might tease you for adopting what seems like a military style, using the 24-hour system can significantly reduce confusion. For instance, instead of “midnight” being represented as “12 am,” it is simply denoted as “00:00,” reflecting the start of the day.

The transition becomes slightly more unfamiliar after 1 pm, which becomes “13:00,” and so forth until midnight. However, the question of whether midnight should be represented as “00:00” or “24:00” remains open for debate.

Ultimately, the choice between the 12-hour and 24-hour systems boils down to personal preference and the context in which time is being communicated.