A.M. and P.M. are two abbreviations you’ve most definitely heard a lot in your life; everyone has! But you might not know exactly what they mean. These two little abbreviations are used to indicate whether a time is in the morning or in the afternoon.
But don’t let the simplicity of these abbreviations fool you. These terms have a rich history and a few quirks that make them worth understanding. I’ll go over all the details in this quick guide!
What Do A.M. and P.M. Stand For?
As a kid, I always thought “at morning” and “post morning.” But actually, the appreciated term A.M. stands for “ante meridiem,” which is a Latin term for “before noon.” It’s used to indicate that a time is in the morning, before 12:00 p.m. (noon). We also know it as the hour after midnight.
But P.M., on the other hand, stands for “post meridiem,” which is Latin for “afternoon.” It’s used to indicate that a time is in the afternoon or evening, after 12:00 p.m. (noon), or the hour before midnight.
What Are A.M. and P.M. of Time?
The simple terms A.M. and P.M. are based on the traditional way of measuring time, which is based on the position of the sun in the sky. The ancient Romans divided the day into two 12-hour periods, with the first period starting at sunrise and ending at noon (when the sun’s at the highest point in the sky) and the second period starting at noon and ending at sunset.
Remembering the Difference Between A.M. and P.M.
One way to remember the difference between A.M. and P.M. is by thinking of the word “ante” (A) as meaning “before” and “post” (P) as meaning “after.” So, A.M. is before noon and P.M. is after noon.
Another way to remember is that the alphabet begins with the letter “A,” and the morning is the first part of the day. Similarly, the letter “P” is the 16th letter of the alphabet, and the afternoon/evening is the second half of the day.
Does the Whole World Use A.M. and P.M.?
Fun fact! In some countries, instead of using A.M. and P.M., they use a 24-hour format, where the day starts at 00:00 (midnight) and goes up to 23:59 (11:59 P.M.). It’s really just the Americas that adopt the use of acronyms.
Nowadays, with the rapid dawning of technology and digital devices, it’s becoming even more common to see time represented in the 24-hour format. But the use of A.M. and P.M. is still prevalent, particularly in written and spoken language. When I’m writing, it’s what I use, mostly because I know the average reader is going to understand it better.
How to Properly Use A.M. and P.M.
In terms of usage, you can use A.M. and P.M. for both formal and casual settings; it depends on the context. In a more formal setting, you might use them in a business meeting, like, “The meeting starts at 9 A.M.” In a casual setting, you might use them in a text message to a friend, such as, “I’ll be home by 6 P.M.”
Using A.M. and P.M. in a Sentence
- I’m going to meet my friends at 8 A.M.
- I always wake up at 6 A.M.
- The party starts at 7 P.M.
- I’m going to bed at 11 P.M.
- I used to pre-tape morning television shows so I could sleep in and watch them in the P.M.
Spelling and Capitalization of A.M. and P.M.
Their official spelling is with the periods: A.M. and P.M. However, over time, language has evolved, and the spellings am and pm are acceptable when written in a certain way.
- The event will begin at 11 am.
- You have soccer practice at 5 pm.
Also, using lowercase letters with or without periods is acceptable and actually more commonly used today.
- School starts at 8 a.m.
- I stayed up until 11 p.m. watching the new season of my favorite show.
Difference Between a 24-Hour Clock and a 12-Hour Clock
The difference between a 24-hour clock and a 12-hour system is in the way that time is measured and represented.
A 12-hour clock, also known by most people as a standard clock, divides the day into two 12-hour periods: one period from midnight until noon and another period from noon to midnight. The first period is indicated by A.M. (ante meridiem) and the second period by P.M. (post meridiem).
This common system is based on the traditional way of measuring time, which is based on where the sun is in the sky. It uses the numbers 1 to 12 to indicate the hours, and the day starts at 12:00 A.M. (midnight) and ends at 11:59 P.M. Basically, it’s the AM-PM clock we all use today in households and businesses all over the world.
A 24-hour clock, more commonly known as military time, is different and divides the day into 24 equal hours. The day starts at 00:00 (midnight) and goes up to 23:59 (11:59 P.M.). It doesn’t use A.M. or P.M. at all, and it’s based on a continuous count of hours starting from 0 to 23.
The system is widely used in the military, in transportation, and some other fields, as it eliminates the need for A.M./P.M. distinction, and it’s less prone to confusion. Just think of any military movie or T.V. show you’ve ever watched. They probably used terminology like “we meet at oh eight hundred hours” which basically means 0800 on their clock and translates to 8:00 A.M. on the 12-hour clock.
The Clock Is Set
You should have a better understanding of the current definition of A.M. and P.M. now. Just remember that they’re two terms used to indicate whether a time is in the morning or afternoon. A.M. stands for “ante meridiem,” meaning “before noon,” and P.M. stands for “post meridiem,” meaning “afternoon.” They can be used in both formal and casual settings, and it’s important to remember that. Hope my guide has helped!