Why Do We Really Use The 12-Hour Clock?

We use the 12-hour clock frequently in our daily lives. We have grown accustomed to it over time. But the odd fact about it is that it is quite confusing to use. We all experienced difficulty in using it when we were taught the 12-hour clock system as children. Did we forget its challenges as we grew up? Or do the challenges of the 12-hour clock system go quietly unnoticed in our society every day? When was the last time you got confused between 12:00 during daytime and 12:00 during nighttime?

Most recently, I heard a story from my parents that they showed up 12 hours late for a train. The train had long left. They had booked the train that had departed at 02:00 in the morning and thought it was for 02:00 in the afternoon. The train ticket did not indicate this difference clearly enough (at least according to my parents). Sure, we have invented the concept of a.m. (ante meridiem from Latin) and p.m. (post meridiem) to distinguish between day and night. But isn’t it simply easier to have a 24-hour time clock (cycling from 00:00 hours to 24:00 hours)? All these questions are circling around in my head. If you’ve been bitten by this bug as well, join me in this brief journey to answer some of these questions about the 12-hour clock.

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The Origins

We trace the origins of the 12-hour clock back to old Mesopotamia and ancient Egypt. These civilizations seem to have split the day into 2 cycles: a day cycle which could be tracked by the movement of the sun, and a night cycle which could be tracked by the movement of the moon and the stars. This could also explain how we came up with the concepts of a.m. and p.m. The Egyptians for instance used the 12-hour clock face in both sundials as well as in their water clocks (water clocks were used to track time after sunset). Fast forward to this day and age, the 12-hour clock has grown dominant in its usage in a whole host of countries, including the United Kingdom, the United States, Canada, Australia, New Zealand, etc.

But Why 12?

12 just seems to be a random choice, isn’t it? For instance, it could have been 11, but it had to be 12! Why? For starters, a year has 12 lunar cycles. The ancients took notice of that. Furthermore, ancient cultures such as Mesopotamia used a base-12 counting system. We use a base-10 counting system today because most of us have 10 fingers. But back then in these ancient cultures, they used the features of the hand shown in the image below to count. The typical hand just happened to have 12 features, which made counting the number of yearly lunar cycles with one hand possible. Furthermore, 12 is an easily divisible number (divisible by 2, 3, 4, and 6, for instance).

This made calculating halves, thirds and quarters easier for people without having to resort to fractions. All in all, there was no single reason why it had to be 12. A whole bunch of reasons contributed to why 12 came up on top. So, it turns out that the choice of 12 was not so random after all!

Why Do We Still Use the 12-Hour Clock?

Even when we consider all of these advantages the 12-hour clock offers, common sense says that a 24-hour clock provides most of its advantages minus the confusion. So, I’d argue that it’s not the best system. But when it comes to mass adoption of systems, network effects make it extremely difficult to change deep-rooted systems. It is often the case that the most popular system thrives because the majority of people are used to that system and/or have built systems and subsystems that depend on the original system.

A classic example of this is the most common English keyboard layout. The keys are actually not placed the most ergonomically for human friendliness. Inventors placed the key layout this way for the mechanical efficiency of the typewriters. We no longer use typewriters, but the system still thrives today. Some companies tried to introduce more ergonomic keyboard layouts in the past, but they failed in mass adoption. Similarly, the 12-hour clock may not be the best clock system humanity has ever developed, but it still thrives today due to its deep-rooted historical origins and widespread network effects. Whether we like it or not, we seem to be stuck with it. So, we might as well try to be aware of its limitations and compensate accordingly. At least for now, we were able to answer some of those pesky questions circling in our heads.

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Further reading that might interest you: Why Does Temperature Have No Upper Limit? and How To Use Mathematics To Choose A Life Partner?