Full Form of AM and PM: AM Full Form is Ante Meridiem (‘before mid-day’) and PM Full Form is Post Meridiem (‘after mid-day’). The 24 hours in a day is divided into two parts – AM and PM. In other words, Ante Meridiem represents ‘midnight to noon’ and Post Meridiem represents ‘Noon to Midnight’. The terms are derived from Latin words where ‘meridies’ means ‘midday’; ‘ante’ means ‘before’; and ‘post’ means ‘after’.
Also, most people tend to get confused with the usage of AM and PM for 12 O’ clock. Since the word ‘meridiem’ refers strictly to noon or midday, the term AM and PM does not apply for 12:00. The time 12:00 has to be used without any suffix. It is either 12:00 or 12:00 midnight in a 12-hour clock.
Full Form of AM and PM – Additional Information
Time is an interesting mystery, which we have, for our own convenience, described it in terms of mathematics, physics, and clocks. While we have yet not clinched any strong evidence as to what exactly time is; whether it is a just a figment of imagination or has something way murkier behind its existence. Whatever the case may be, time remains, at least for now, an oblivion case.
Like I have mentioned before, clocks are one of the methods by which we define time. It is reasonable, of course, because not every human being is a mathematics or science genius to fashion his or her vocabulary with technical words. Keeping beside the general stuff, which we shall anyway have in our consideration throughout the discussion, let us begin with some preliminary information that everyone must have.
We shall keep our focus particularly on the format of time. We shall begin with the 6-hour time format followed by 24-hour time format briefly followed by an extensive discussion of our main theme, which is a 12-hour format that comprises two essential components namely, AM that stands for Ante Meridian and PM that stands for Post Meridian.
Before we move to 24-hour format, we shall discuss the now archaic system of time, 6-hour clock system. The system is a traditional system of time that is prevalent in the Thai language. It was formerly used in languages like the Lao language and the Khmer language. Though like the 24-hour clock system it counts 24 hours every day but the time period is divided into four quarters. For each quarter, the number of hours counted is six.
Barring the sixth hour in every quarter, the hours in each quarter are indicated in period denominated words, which are mong chao that indicates the first half of the day (from 7.00 to 12.59); Bai … mong that indicates latter half of the day (from 13.00 to 18.59); … thum that indicates the first half of the night; Ti … that indicates the latter half of the night time. These terms have been believed to have originated from the sounds produced by the conventional time keeping inventories.
People used to play the gong when the hours in day were announced whereas the drum was played to announce hours in night time. This explains the term mong, which is similar to the sound of the gong and thum, which is similar to the sound produced by the drum. In Thai, the word Ti is used to indicate the hit and is believed to have come from the activity of hitting the time keeping inventories. Morning and evening are indicated by the words Chao and bai respectively.
Now the exception, which is the sixth hour of each quarter is indicated by different terms. At dawn, the sixth hour of the quarter is referred to as yam rung whereas the sixth hour at the dusk is referred to as yam kham. Kham and rung mean dusk and dawn respectively. The time of midday and midnight is referred to as thiang/thiang wan and thiang khuen respectively. Both of these terms regionally mean midday and midnight. .
This system of time has been used since the time of Ayutthaya Kingdom however, it was codified in the year 1901 by King Chulalongkorn. It was codified in Royal Gazette 17:206. Now, the use of these terms and the time format is limited to colloquial use.This system was eventually abolished in Laos and Cambodia during the French intervention and the French system of the time was then used.
Of the two standard time conventions in the world, the 24-hour format is one of them. It is the time convention wherein the day occurs from midnight to midnight. The time format is, as its name suggests, divided into 24 hours. The time in this convention is indicated in hours, which have been passed since midnight. That is from 0 hours to 23 hours. This system is a comparatively popular time notation in the world as of now.
The time convention is used by an international standard by the name ISO 8601, which is an international standard that covers the transmission of date and time data and is issued by the International Organization for Standardization (abbreviated as ISO). The 24-hour format is used in medical field for documenting care that prevents any confusion as to the events pertaining to the medical history of a patient. This standard of time is commonly known as Military Time in countries like Canada, India, the United States and other countries where the 12-hour format is still prevalent.
Now that we have discussed the 24-hour format, we shall move closer to our main discussion on the less popular 12-hour format. 12-hour time format is one of two prevalent standard time conventions in the world in which the time (24 hours in a day) is bifurcated into two periods. Those two periods are AM, which as mentioned above stands for Ante Meridian, and PM, which stands for Post-meridian. The former expression is a Latin phrase, which means before midday and the latter expression, which is obviously another Latin phrase, stands for after midday.
In this system of time, each period comprises 12 numbers, in which the number 12 functions as a zero, followed by 1, 2, 3, and so on until 11 in a sequential order. The time cycle begins from 12 midnight (12 a.m.) and continues to 12 noon, which is understood by 12 p.m. and then continues to the midnight to mark the end of the day.
Let us explore the history behind the development and use of this kind of time format. The origins of the 12-hour clock format can be found in ancient civilizations like Egyptian and Mesopotamian, which are known to have ushered in a new age of human development. Ancient Egyptian civilization is known to have developed many inventories like sundials that were for day time usage and water clocks that were night time usages. These inventories have been found in various Egyptian tombs and even that of the tomb of Amenhotep, who was a renowned Pharaoh. These inventories or let us call them clocks used to divide time into 12 hours, much like the modern 12-hour clock system.
The great Roman empire too had used the system of 12-hour clocks. The daylight was bifurcated into 12 hours though there may be variations in a year and the night was bifurcated into four watches. Even though there were differences in the then and now prevalent system, the fundamentals were pretty much similar.
The world witnessed the first mechanical clock during the 14th century. Many civilizations used dials that presented all 24 hours, however, in areas in and around Northern Europe dials used indicated all 12 hours based on Roman Numerals. This system of using Roman numerals for indicating hours is known as Double XII system and could be seen in some clocks these days. The system of 12-hour clock was used for quite a substantial time of British empire.
In the 15th century, this system of 12-hour clock became a standard for indication of time in the British empire, particularly in Northern Europe. The use of the 24-hour system was reserved for special uses such as in chronometers and astronomical clocks. Today most analog clocks use the 12-hour system, which is more convenient for such types of clocks.
The use of 12-hour clock system and 24-hour clock system varies. For example, many countries use the 12-hour clock system in spoken system whereas the 24-hour clock system is used for the written system. What’s more interesting that non-English speaking countries might not even know what a.m. and p.m. stand for and what their respective uses are. The same goes for use in computer systems. The default time format in most of the operating systems is the 24-hour time format however, one can change it to 12-hour format as per one’s convenience.
Now that we have dealt with 12-hour format in general, let us discuss two important components of this category of format. These two components, AM and PM have great importance in the 12 hour system and therefore, must be understood properly. Once you have understood these terminologies then the purpose and functioning of the 12-hour system would be a piece of cake for many to understand.
AM – Ante Meridian (Before Noon) and PM – Post Meridian (After Noon):
These two must be understood together and therefore, will be dealt with under the same head. Both terms a.m. and p.m. are abbreviated forms of Latin phrases namely, ante meridian and post meridian respectively. These two phrases mean before noon and after noon in English and have relevance as far as the 12-hour clock system is concerned. These terms are also written as AM and PM and am and pm. They are more commonly known in Spanish and English language. In Greek, they are used as π.µ. and µ.µ. respectively. It is rare to see people using the formal expressions that are “before noon” and “after noon”, as most of the use of 12-hour clock is verbal only.
Now let us discuss the typographical aspects of both these terms. As mentioned earlier that there many abbreviated variants to say ante meridian and post meridian like a.m., p.m., AM, PM, and whatnot, there are still debates on which one is correct. Many books prefer the use of space between the number and the abbreviated forms a.m. and p.m. Many stylebooks suggest that if not suggesting any numeric, then do not use a.m. and p.m. The typography will largely vary with different countries. Thus, one has to adjust with the country usage.
There is a lot of confusion regarding the use of both these abbreviated terms a.m. and p.m. Many people find it confusing as far as what time 12 p.m. and 12 a.m. suggest. Literally speaking, noon is neither before or after, as the full forms of a.m. and p.m. suggest. Thus, technically, a.m. and p.m. do not apply. To sort out this confusion, the American Heritage Dictionary of the English Language (abbreviated as AHD), which is an American Dictionary that Houghton Mifflin publishes, has appended a note on this issue, which says and I quote “By convention, 12 AM denotes midnight and 12 PM denotes noon.
Because of the potential for confusion, it is advisable to use 12 noon and 12 midnight.” There are other interpretations made by other persons and institutions as well. In the book Mapping Time, the author E.G. Richards gave a diagram suggesting that 12 a.m. indicates noon and 12 p.m. indicates midnight. This interpretation is quite contrary to the common use.
Many American style books and Frequently Asked Questions (abbreviated as FAQs) on the webpage of the National Institute of Standards and Technology (abbreviated as NIST) suggest that one should use noon or 12 noon and midnight or 12 midnight to avoid confusion because there is no definite answer to the question raised. So, avoid using 12 a.m. and 12 p.m. The same is recommended by the Canadian Press Stylebook, which in its 11th edition published in the year 1999 states that it is advisable to write 12 noon or 12 midnight instead of 12 a.m. and 12 p.m.
The FAQs on the webpage of the Britain’s National Physical Laboratory mentions that unless there is any option, it is recommended that the use of the terms 12 a.m. and 12 p.m. should be avoided. The issue is contentious and has not been resolved. Many American style books have developed this method of referring to both these time periods as 11.59 p.m. and 12.01 a.m. This is becoming increasingly common in American legal system, particularly in contracts and for announcing schedules for trains, airplanes, buses, etc.
This problem does not arise when the time format is used is 24-hour time format. This category of 24 hour format because it uses 00.00 for indicating midnight at the beginning of the day and 12:00 is used for indicating noon. In fact in the 24-hour time format, 24:00 can be very conveniently used indicate midnight at the day’s end.
In the United Kingdom many methods have been developed to alleviate the confusion in the use of these terms. Take for example TV mag, Sun newspaper from the date December 17, 2005 makes use of noon for 12.00 and midnight for 0.00. The sequential enumeration begins with a.m. and p.m. but these have not been used again. Sometimes, one can see use of 12 midnight in sub-listings. Daily Telegraph, London’s prominent newspaper, makes use of the terms “12.00 noon” and “12.00 midnight” in its respective individual listings.