Have you ever tried to tell someone to meet you at noon but weren’t sure whether to write 12:00 a.m. or 12:00 p.m.? Or maybe got into a heated argument regarding which to use?
Well, I have good news and bad news.
The bad news is that you’ve probably been wrong about it. Here’s why:
The a.m. in 12:00 a.m. is an abbreviation for ante meridiem, a Latin term for “before midday”. Unsurprisingly, p.m. is an abbreviation for post meridiem, meaning “after midday”. Midday, in this case (strictly speaking), is noon. Since noon can be neither before nor after itself, technically, we shouldn’t be using a.m. or p.m.
So what’s a person to do? Well, that’s the good news: not only is there a solution, but it results in far less confusion.
Use noon to refer to 12:00 during the day and midnight to refer to 12:00 during the night.
This method has support of several style guides and dictionaries:
Chicago Manual of Style
“Except in the twenty-four-hour system, numbers should never be used to express noon or midnight (except, informally, in an expression like twelve o’clock at night). . . . And the term 12:00 p.m. is ambiguous, if not illogical.” (, 9.39)
American Heritage Dictionary of the English Language
“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.” (“AM”, 5th Edition, 2011)
Canadian Press Stylebook
“Write noon or midnight, not 12 noon or 12 midnight.” (11th Edition, 1999, p. 288)
Alternatively, you could stick with a 24-hour clock, indicating noon as 12:00 and midnight as 24:00 or 0:00; however, unless it’s clear that you use a 24-hour clock, readers may not know what 12:00 refers to.
So, maybe just stick with saying “noon” and “midnight”.
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