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What Do AM & PM Really Mean?

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  • Tip Bones

If you've ever carefully adjusted your alarm to read 'AM' versus 'PM,' or vice versa, you're familiar with the concept of the common initialism. Generally speaking, AM refers to the morning, the time before noon, and PM noon and after. But other than confusing our digital alarms, what purpose does this abbreviation serve, and what does it mean?

When we say 'before' or 'after' noon, it doesn't seem to be reflected in the abbreviation itself. But it actually comes from the Latin phrase ante meridiem, meaning literally before the midpoint of the day, and post meridiem, meaning after the midpoint. That midpoint of the day, of course, is noon

But what about noon and midnight? They are neither perfectly before or after noon. Noon is itself, and can't be before or after. Midnight might be considered both, as it is basically the midpoint to the midpoint, so to speak. AM became the designation of midnight because it starts the new day, and PM was assigned to noon just to have its opposite, because starting PM after 12 would be confusing for everyone.

You can use plain old 'M' to mark noon itself, but almost nobody does this, and your meaning might be unclear. Maybe this is is good time to set to a 24 hour clock!