AM and PM Full Form

Whenever we check the time or tell anybody the time, we often accompany it with units such as am and pm But we don’t know what these terms mean. We know that am starts at night and pm starts at noon. We use am for the first 12 hours of a day and pm for the next twelve hours a day.

AM stands for ante merīdiem and PM stands for post merīdiem. These are Latin phrases that mean before midday and after midday, respectively. So basically, the 24 hours of the day are divided into two groups as before midday hours and after midday hours.

Use of AM and PM

There are two formats of clocks, i.e., 12 hours clock format and 24 hours clock format. Since a day is made up of 24 hours, it’s easy to tell the time in the 24 hours format without using any unit. However, in a 12 hours format, each number is repeated twice a day. 

While it isn’t much of an issue when you’re telling the current time as it’s easy to know whether it’s day or night. However, when you need to document when something takes place for future references, you must mention whether it’s 1 o’clock at night or 1 o’clock in the afternoon. Here, the a.m. and p.m. units come into use.

Full form of AM and PM

The abbreviation a.m. stands for ante meridiem, and the phrase post meridiem is abbreviated to p.m. Since the 12-hour format of the clock is widely popular, the abbreviations a.m. and p.m. have gained quite some popularity. However, sometimes these abbreviations are not mentioned while stating a time. 

In such cases, we have to determine whether it’s a.m. or p.m. for ourselves based on the context of the time. For example, if someone invites us for dinner at 8 O’clock but fails to mention a.m. or p.m., we take it to mean p.m. based on the context of “dinner.”

Origin of AM and PM

The abbreviations am and pm do not expand into full English forms. They are Latin phrases. AM is the Latin phrase “ante meridiem,” before midday. And PM is a Latin phrase “post meridiem,” which means after midday. 

Hence, all the hours which occur from 12 at the start of a new day to the noon of that day are followed by a.m. And all the hours that fall after 12 O’clock in noon are followed by the unit p.m. These units gained popularity around the 17th century AD

AM

AM or the ante meridiem is a unit used in a 12-hour clock format to indicate hours that fall before noon. These hours consist of a total of 12 hours. They begin at 12:00 am, the first hour of any day. They extend up to 11:59 am just before noon, which is the last hour of am. It covers all the night after 12 am, early morning hours right until noon.

PM

PM or the post meridiem is another unit of a 12-hour clock format used to indicate hours of days that fall in the afternoon. They are a total of 12 hours, beginning with 12 and followed by one up to 11. The first hour of PM begins precisely at noon, 12:00 pm. 

From this point onwards, the second half of the day starts. PM covers all the afternoon hours, evening hours, and a few of the night hours. The last clock time with the unit PM is 11:59 pm which also marks the end of the day. As soon as the clock shows 12 a.m. again, the beginning of a new day is observed.

The need for AM and PM

We needed to invent these abbreviations in the first place because of the 12-hour clock format. The day was divided into two cycles based on day and night time. Each of these cycles consisted of 12 hours each.

Instead of using 24 hours to represent all times, a clock system based on these cycles was considered more convenient. To implement this, there was a need to come up with something to distinguish between these two cycles. 

This is why AM and PM were invented. The physical clocks were designed on the same phenomenon of two cycles in a day. Hence, there are only 12 numbers on a watch even though there are 24 hours in a day. However, an analogue clock doesn’t show us these units. But digital clocks or clocks in our computers or phones show us time with AM and PM units when set to a 12-hour clock format.

Conclusion

The full forms of AM and PM are ante meridiem and post meridiem, respectively. They are used in a 12-hour clock format to distinguish two clock cycles from one another. The hours which use AM occur from the start of the day until noon. The hours of PM start from noon until the day ends.

To convert 24-hour timings in 12-hour format using AM and PM, you should subtract 12 from numbers higher than 12. Physical clocks were designed in this time format. AM and PM are prominently used today.