AM vs PM | Ante Meridiem and Post Meridiem
AM and PM indicate two sessions of time in a day. They are both different. AM stands for Ante Meridiem, whereas PM stands for Post Meridiem. This is the main difference between the two abbreviations.
AM or ante meridiem means ‘before noon’ in Latin. Post meridiem means ‘after noon’ in Latin. There is a belief that AM means ‘after midnight’. This is so because the time represented by AM is between 12’o clock in the night or midnight, and 12’o clock or noon. The time after noon is understandably called as PM.
It is interesting to note that the time 12’o clock is called either as midnight or as noon. Observe the sentences
1. I expect you will come at noon.
2. He slept at the stroke of midnight.
In the first sentence, you can see that the word ‘noon’ is understood as 12’o clock in the morning, and the word ‘midnight’ in the second sentence, is understood as 12’o clock in the night. Hence, it can be inferred that both noon and midnight cannot be represented either by AM or PM. This is a very important observation to make while representing time with AM or PM.
Sometimes, we do find midnight represented as 12 pm and noon represented as 12 am, but it is not right to do so. In short, it can be said that AM and PM start immediately after midnight and noon or midday respectively. Thus, 00:00 am and 00:00 pm have no meanings at all. They can be simply called as midnight and noon respectively.
It is interesting to note that both the abbreviations are used as adjectives, since they describe the time of the day or the night as the case may be. These are the differences between AM and PM.