AM and PM: What do AM and PM actually stand for?

All there is to know about the 12-hour time system

Everyone uses these abbreviations every day. That said, do you actually know what they stand for? In the past, we could only tell the time with the sun’s position. Nowadays, we are using digital clocks for tracking our daily activities. Most countries use the 12-hour time format, often coupled with the abbreviations: AM and PM. Let’s find out what they mean and their origin.

How does the 12-Hour system work?

The 12-hour system originated from Northern Europe. Then, it was spread globally via the British Empire. Since then, this system is considered the international hour system. The AM and PM convention was only used by some English-speaking nations and former British colonies, as well as a few other countries such as the United States, Canada (except the province of Quebec), Australia, New Zealand, and the Philippines.

The 12-hour system equally divides the 24 hours of a day into two halves of 12 hours. The first 12 hours are designated as AM, which runs from midnight to noon. The second 12-hour is marked as PM, which runs from noon to midnight. The abbreviations of AM and PM are acquired from the Latin language. The abbreviation of AM stands for “ante meridiem”, which translates to “before midday (noon)”. Note that you can also write it as follows:

  • a.m.
  • am
  • A.M.

PM on the other hand stands for “post meridiem”, which translates to “after midday (afternoon)”. PM can also be written as follows:

  • p.m.
  • pm
  • P.M.

Uncertainty on Midnight and Noon

One confusing point about the 12-hour system is which abbreviation should be used for noon and midnight. Don’t worry anymore, here is an easy explanation of how it works.

Each half consists of 12 hours numbered as follows:

12 (sometimes shown as 0),1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 11.

The 24-hour/day cycle begins at 12 midnight which is usually referred to as 12:00 AM.

Then, the circle runs through 12 noon which is usually referred to as 12:00 PM and continues until midnight at the end of the day.

And there you go, not so bad is it? Luckily, most of the digital clocks and watches we use nowadays indicate midnight as AM and noon as PM automatically. Another way to avoid confusion is that you can use the term 12-noon and 12-midnight, instead of 12 PM and 12 AM.

Military time

Military time is a bit different since the coordination of military actions needs an accurate and unambiguous comprehension of time. As in the past, the solar day was the primary measure of time using a full-day timetable. The military institutions utilize a similar 24-hour clock format and do not separate hours from minutes. For example, instead of noon or 12:00 PM (civilian time), military time indicates “1200” which is pronounced as “twelve hundred”.

This pronunciation is also used for denoting time in radio communication. This format is the most exact way to mention the time and being used for navigation and scheduling. Last but not least, in the practice of medicine, the 24-hour clock is also commonly used in the documentation of care. Indeed, they use it to prevent any ambiguity when events happened in a patient’s medical history. Similarly, busses and trains sometimes use the 24-hour clock format for their timetables.

What are the advantages of using the AM and PM abbreviations?

Here are the 2 main reasons why using AM and PM is convenient for all of us:

  • An easy way to understand time for everybody

Adjusting time measurements can be difficult when you fly from one place to another. With the AM and PM format, it is easier for people who are traveling to adapt to a new timezone. For that reason, this system played a big part in establishing an outline of time that everybody could agree on.

  • As they say, time is money!

As we all know, farmers used to keep track of time with the natural use of the sun’s position in the past. Thereafter, when the modern era came, lots of them abandoned the fields and changed their job to work in the city. Therefore, these rural workers had to adapt to a more modern time system instead of the good old traditional rural scheduling they were used to. By providing work shifts and time cards, it helped workers to keep an accurate track of their working shifts. Having the AM/PM abbreviation directly beside the time was clearly indicating if it was morning or afternoon without any confusion. In other words, no more excuses for workers to not show up on time!

With that out of the way, you now know how to define AM and PM without a doubt. Anyhow, most of us have wristwatches, cell phones, as well as many other gadgets to know the time. Let’s be honest, we have it pretty easy these days!

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