When it is three o’clock at night, what will the clock look like? We’ve got two possible answers, three o’clock am and three o’clock pm.
Let’s start by comparing our two possible answers. What’s the same and what’s different about them? Well, the thing that’s the same about them is that they both show three o’clock written digitally. Any o’clock time that’s written digitally has two zeros after the two dots. And because we’re thinking about the time three o’clock, the number before the two dots is three.
So, both of our times show three o’clock. But we’re looking for the time that shows three o’clock at night. And the clue to this is in the two letters that follow both times, am and pm. Let’s draw a timeline to help us understand what am and pm represent.
Imagine this is one long continuous line. The start of a new day is 12 o’clock midnight, the middle of the night. Let’s label six o’clock, six o’clock in the morning. Then we come to another 12 o’clock. This time it’s 12 o’clock in the middle of the day. We also call this time noon. Let’s mark six o’clock in the evening. Eventually, we reach midnight again when a new day begins and we start all over again. That’s why we can draw an arrow here to show that the timeline continues.
The letters am and pm stand for two Latin phrases, ante meridiem and post meridiem. The word meridiem was the Latin word for the middle of the day, for noon. Ante means before, so ante meridiem before noon. So, any time between midnight and midday is an am time.
pm stands for post meridiem. Post means after, after midday, or afternoon. And so, pm times are anytime from midday all the way through to midnight. Where can we label three o’clock on our timeline? Well, three o’clock happens twice during a day. The first time is between midnight and six o’clock, an am time. This is three o’clock am.
The second three o’clock in the day is between midday and six pm. It’s three o’clock in the afternoon, three o’clock pm. And so, if it’s three o’clock at night, which of our two clocks is correct? Is it three o’clock am? Or three o’clock pm? An easy mistake to make is the thing that all the nighttime times are pm times. But remember, when we get to midnight, the time becomes am. And so, at three o’clock at night, the clock will read 3:00 am.