why do we use am and pm

Most English speakers know that a. m. refers to the hours from midnight and noon, and
p. m. to the hours from noon and midnight. But what do these ubiquitous abbreviations stand for? The term we associate with the morning, a. m. , is an abbreviation the Latin phrase ante merdiem meaning before midday; p. m. is an abbreviation of post merdiem, meaningyou guessed itafter midday. These two terms help keep ambiguity at bay in the 12-hour time system.


There is a third, lesser-known abbreviation in this system: m. from the Latin merdis meaning midday means noon. However, m. is rarely used and might confuse readers or listeners should you casually drop it into conversation or insert it into your writing; noon is conventionally expressed as 12 p. m. or 12:00 p. m. and midnight as 12 a. m. or 12:00 a. m. In formal writing, it is best to lowercase both a. m. and p. m. and retain the periods (as opposed to writing them AM / PM or am/pm ); however, should you choose to use a different format, the most important rule is to be consistent throughout your piece.


Note that when a. m. or p. m. end a sentence, as in The train is arriving at 10 p. m. , it is not necessary to place an additional period at the end. And, for our final writing tip, since these abbreviations specify an hours relation to noon, it is not necessary to use morning, evening, night, or oclock with them. what a. m. and p. m. stand for.


And no, its not, as my first grade teacher told me, After Midnight and Past Midday. LIES!!! Though, funny enough, not really that far off the translated versions of the Latin words for which a. m. and p. m. actually do stand for. It turns out, a. m. stands for ante meridiem, which is Latin for Before Midday; p. m. stands for Post Meridiem, which is Latin for After Midday.


Interestingly, this finally clears up for me one of the interesting quirks of the 12 hour clock system where time counts from 12 a. m. to 1 a. m. and likewise goes from 11 a. m. to 12 p. m. , which always seemed odd, but now makes perfect sense given what a. m. and p. m. stand for.

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