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The Actual Truth About Midnight:
Is It Really 12 AM Or 12 PM?

(And Which Of Those Two Times Is Actually Noon?)

The Definitive Answers

- by -

Bob Bishop ("Mr. Logic" on Radio Station KSCO)

It is a commonly accepted notion that the midnight hour is an AM hour. (Some naive individuals even seem to think that the letters "AM" are actually an abbreviation for "After Midnight".) And some misguided individuals (such as attorneys ) make the foolish claim that it isn't actually AM until one minute past midnight. And still others seem to incorrectly think that midnight is neither 12 AM nor 12 PM.

But now, let's set the record straight, once and for all. (However, let me warn you in advance: I am not going to mindlessly "parrot back" the "fashionable" answers to the questions about noon and midnight. Instead, I'm going to present the correct answers to those questions, along with the explanations of why those answers are correct.)

If all you're interested in are the final "bottom-line" answers to the questions about noon and midnight, (and if you don't care about actually understanding those answers), then let me just state them here:

Noon is actually twelve o'clock AM (followed by 12:01AM, 12:02AM, ... 12:59AM, 1:00PM)

Midnight is actually twelve o'clock PM (followed by 12:01PM, 12:02PM, ... 12:59PM, 1:00AM)

Now, if you don't agree with those answers (or equivalently, if you don't understand why those are the correct answers), then let me explain them to you:

The Explanations

First, let's consider what the letters "AM" and "PM" mean: They are abbreviations for the Latin expressions "Ante Meridiem" and "Post Meridiem," respectively. (Ante and post are Latin for "before" and "after," respectively. Meridiem is the Latin word for "meridian," the imaginary great circle on the celestial sphere, which passes through the point in the sky directly overhead, and through the point on the horizon directly south of the observer.)

Every day the sun spends essentially half of its time to the east of the meridian (i.e., ante meridiem), and half of its time to the west (post meridiem). And the crossover point (near the middle of the daylight portion of the day) defines local noon, the time when the sun reaches its highest point above the horizon.

Because the meridian is defined in terms of an observer, the exact time at which local noon occurs depends on where the particular observer is located. Therefore local noon seldom (if ever) occurs exactly at "clock-time" noon (i.e., twelve o'clock). So if one were to interpret the meaninings of AM and PM literally, then the exact time at which "AM becomes PM" would not be at 12 o'clock, but would instead occur at different times for observers at different locations.

Even adopting the concept of "standard meridians" (i.e., 24 fixed meridians, one for each of 24 time zones) would not solve the problem because the sun does not make meridian crossings (of any meridian) in exactly 24 hour intervals. Since the orbit of the earth around the sun is not a perfect circle, the times of the sun's meridian crossings slowly change from day to day. Over the course of a year, this daily drift (known as the "equation of time") can amount to as much as about plus or minus 18 minutes.

And to make matters even worse, during some months of the year parts of the world are on Daylight Savings Time (when the sun actually crosses the meridian an hour later than our clocks would otherwise indicate). Should we therefore refer to the noon hour as being PM during the winter, but AM during the summer?

When specifying clock times, it is clearly impractical to try and interpret the meaning of the term "meridian crossing" (and "AM" and "PM") in their literal senses. Instead, we can just loosely refer to the term "meridian crossing" as meaning "around noon time".

Therefore, 1 PM means that one hour of time has elapsed since the previous meridian crossing (i.e., since noon), 2 PM means that two hours have elapsed, etc. When we finally reach eleven hours since the previous meridian crossing, we call it 11 PM. (I.e., eleven hours "post meridiam").

Is that clear to you? If not, then let me repeat: 11 PM means that eleven hours of time have elapsed since the previous meridian crossing (i.e., since noon).

Now, let me ask you a "real toughie" question: If we wait one more hour (past 11 PM), how many hours will have elapsed since the previous meridian crossing ? In other words, how many hours will have elapsed since noon?

Well (duh!), the answer is (of course): twelve hours will have elapsed since the previous meridian crossing. (I.e., twelve hours "post meridiam", or 12 PM). But one hour past 11 PM is midnight.

So, there you have it! Midnight is 12 PM!

"But," you might argue, "Midnight can also be thought of as being twelve hours before the next meridian crossing. Therefore, shouldn't it be equally valid for midnight to be called 12 AM?" (I.e., twelve hours "ante meridiem")

No! Because the number in front of the "AM" letters indicates the number of hours (of the new day) that have already elapsed prior to the next meridian crossing. Since the new day starts at midnight, that number in front of the "AM" letters therefore represents the number of hours that have elapsed since midnight. (For example, 1 AM means that one hour has elapsed since midnight, 2 AM means that two hours have elapsed since midnight, etc.) Therefore, attempting to refer to midnight as being "12 AM" would be tantamount to making the absurd claim that midnight occurs twelve hours after midnight!

Now, 12 PM cannot refer to both midnight and noon. And we've just shown that 12 PM refers to midnight.

Therefore, Noon is 12 AM (as can be easily verified independently by using similar arguments).

Still not entirely convinced? Then let's continue with the discussion . . .

In order to correctly answer the questions about AM and PM, you only have to know how to count.  (You do know how to count, don't you? It's easy! For example, if you already have ten apples and someone gives you another apple, you then have eleven apples. And if they give you one more apple, you now have a total of twelve apples. You don't have a total of twelve bananas!  But yet, some fools seem to think that if you already have eleven of the "PM" hours and you add one more hour to it, you suddenly end up with a total of twelve of the "AM" hours! )

Remember: Once you begin counting the "PM" hours (1 PM, 2 PM, 3 PM, etc.), you must continue counting those "PM" hours (10 PM, 11 PM, 12 PM), until you reach the "AM" hours. Then, when you finally do reach the "AM" hours, you begin counting all over again, starting with the number "one" (i.e., 1 AM, 2 AM, 3 AM, etc.).

As you should know by now, whenever you count anything (be they hours of the day, fingers on your hand, or chickens in a coop), you never start counting them by beginning with the number "twelve"! Therefore, the very first "AM" hour of the day is not twelve AM. The very first "AM" hour of the day is one AM. And correspondingly, the very first "PM" hour of the day is one PM.

If the hours of the day had been assigned meaningless non-numerical labels (such as "QMJ o'clock", "BXF o'clock", "TLA o'clock", etc.) instead of numerical values (such as "1 o'clock", "2 o'clock", "3 o'clock", etc.), then it would have been permissible to declare all of the morning times to be "AM" times only, and all of the afternoon times to be "PM" times only. (And the exact instants of noon and midnight themselves would have been neither "AM" nor "PM".)

But meaningless labels were not assigned to the hours of the day. Instead, numbers were assigned to them. And those numbers (along with their corresponding "AM/PM" designations) are measurements of elapsed time. For example, 12:01 PM means twelve hours and one minute have elapsed since noon (i.e., since the previous meridian crossing).

To further clarify the concepts of "AM" and "PM", let's return to the moment of midnight and continue counting the number of hours and minutes that have elapsed since the previous meridian crossing:

12:00 PM, 12:01 PM, 12:02 PM, 12:03 PM, . . . 12:58 PM, 12:59PM, . . .

Now (in one more minute after 12:59 PM), how many hours will have elapsed since the previous meridian crossing?

Answer: 13 hours will have elapsed since the previous meridian crossing. (13 hours "post meridiam".) Therefore one hour past midnight can be expressed as 13 PM, two hours past midnight can be expressed as 14 PM, . . . and so on.

Notice that you are not required to switch from units of PM hours to units of AM hours, just because you've gone past the midnight hour. It's perfectly legitimate to keep counting the PM hours for as long as you like. And similarly for the AM hours: You are not required to switch from units of AM hours to units of PM hours, just because you've gone past noon.*

*And the same kind of discussion holds true for other things as well. For example, there's no physical temperature at which you must switch from units of Fahrenheit degrees to units of Centigrade degrees. Any temperature can be expressed in terms of either of those units. Similarily, when measuring the length of a long piece of string with a ruler, you are not required to switch from units of "inches" to units of "feet" just because you've gone past the ruler's 12-inch mark. You can continue with: "13 inches ... 14 inches ...", etc.

Therefore, any time of the day or night can be legitimately expressed as either an AM time or a PM time, depending on the number that you put in front of the "AM" or "PM" designation. (In other words, you can choose to specify the amount of time that has elapsed since midnight, or you can choose to specify the amount of time that has elapsed since noon.)

Yes, I know. Using a number greater than 12 to refer to a time (such as 13 PM, 14 PM, etc.) may seem a little unnatural at first. But it's really not much different than allowing the idea of "improper fractions" in arithmetic (i.e., fractions whose values are greater than 1.0) . . . such as 5/3. (After all, how can a "fraction" of something be greater than the whole thing? )

Borrowing the word "improper" from the term "improper fractions" (which refers to fractions that are, in a sense, "too big"), perhaps we should refer to times whose numerical portions are greater than 12 (such as: 13 PM, 14 PM, etc.) as being "improper times". However, such times are perfectly valid times, even though those times could be expressed more "properly" as: 1 AM (of the following day), 2 AM (of the following day), etc.

After a little thought, we can infer the following Conversion Rule: To convert between any AM hour and its equivalent PM hour, merely add or subtract 12. For example, one hour past noon could be legitimately expressed as being either 13 AM or 1 PM, two hours past midnight could be expressed as being either 2 AM or 14 PM, etc.

NOTE: When I use a term such as "13:00 AM", I am not referring to some kind of "military time". I'm refering to regular everyday time.

Furthermore, the expressing of time does not have to limit itself to only positive hours (just as a thermometer doesn't have to limit itself to only temperatures that are above zero ). For example, ten o'clock in the morning can also be correctly referred to as being minus two o'clock in the afternoon -- since ten o'clock in the morning is two hours prior to noon. In other words, 10 o'clock AM is equivalent to negative 2 o'clock PM (as can also be verified by the Conversion Rule.)

In fact, noon itself occurs exactly zero hours past noon. And midnight occurs exactly zero hours past midnight. Therefore,

We can refer to noon as: zero o'clock PM, and we can refer to midnight as: zero o'clock AM.

The ancient Romans measured the time of day by creating a sundial, and they used Roman numerals to label the position of the sun's shadow on the dial. Unfortunately, the concept of "zero" had not yet been discovered. (It was still many hundreds of years away.) So they labelled the first hour of the day as "I", and they labelled the noon hour as "XII" instead of "zero". And that convention of measuring time has persisted to the present day, where our 12-hour clocks all start at "1" and go up to "12".

When handling questions about Noon and Midnight, we simply need to be aware that we are dealing with three pairs of opposing concepts:

Noon vs. Midnight
Zero vs. Twelve
AM  vs. PM

Whenever any two of those opposing concepts are specified, the remaining one is then automatically determined as shown in the following table:

Noon Twelve Zero
Midnight Zero Twelve

For example, if we specify "Twelve" and "Noon" then that automatically determines that the time in question is an "AM" time. Similarly, specifying "Midnight" and "AM" automatically determines that the time is "Zero" o'clock. Specifying "PM" and "Zero" yields "Noon" as the correct name, etc.

Many naive individuals who think that the numbers representing the time of day are nothing more than meaningless labels, simplistically think that any time which is later than 12 o'clock noon must be a "PM" time, and that any time which is later 12 o'clock midnight must be an "AM" time. For example, they incorrectly refer to one minute past midnight as being "12:01 AM".

But, as we have already indicated, the numbers that represent the time of day are not merely meaningless labels onto which you can indiscriminately append either an "AM" or a "PM". Instead, each number represents a measure of elapsed time. In particular, one minute past midnight can be expressed as either "12:01 PM " (if we measure the amount of elapsed time since noon ), or "0:01 AM " (if we measure the amount of elapsed time since midnight ).

From your high school science classes, you probably remember that the boiling point of water at sea level has been measured to be 212 degrees Fahrenheit . . . which can also be expressed at 100 degrees Centigrade (or 100 degrees Celsius). So at which temperature does water boil? Is the correct answer 100 degrees? Or is the correct answer 212 degrees?

The proper response to the question would be: "Both numbers are correct, depending on the temperature scale that you're referring to."

Now, here's the important (and hopefully obvious) part of this discussion: When talking about the boiling point of water, you cannot indescriminately combine a temperature number with a different temperature scale. For example, you cannot just grab the number "100" (from the expression "100 dregrees Centigrade") and simply combine it with the word "Fahrenheit" (from the expression "212 degrees Fahrenheit"), and then come to the ridiculous conclusion that water boils at 100 degrees Fahrenheit! (If this isn't ovbious to you, then you'd better quit reading this essay right now! )

As this example about boiling water illustrates, the two components of a measurement (the number part and the scale being used) must remain together. And so, when specifying a time such as one minute past midnight, you cannot merely grab the number "12:01" from the expression "12:01 PM" and simply combine it with the letters "AM" from the expression "0:01 AM", and then come to the ridiculous conclusion that "12:01 AM" is one minute past midnight!

As long as we insist on using the term "twelve o'clock" to represent noon and midnight, we cannot make the statement that any time which is later than noon is a "PM" time, and that any time which is later midnight is an "AM" time. However, if we use the term "zero o'clock" instead of "twelve o'clock", then we can correctly make the simple statement: "Any time which is later than noon is a 'PM' time, and any time which is later midnight is an 'AM' time".*

*(I'm referring to "proper times" only, of course.)

This idea of using "zero o'clock" to express noon and midnight therefore makes a whole lot more sense than the way we currently do it.

[What? You say that your clock doesn't have a zero on it? Well, that's easy enough to fix. Just scrape off the twelve (which never should have been put there in the first place) and paste on a zero instead! ]

When expressing time, the convention that has been adopted is to write the hours, minutes, and seconds (in decreasing order of significance) separated by colon (":") characters. For example, ten minutes and fifteen seconds past seven o'clock in the evening is expressed as "7:10:15 PM" (since hours are more significant than minutes, and minutes are more significant than seconds).

But years, months, and days are also expressions of "time". And so, when expressing time, it's logical that we should also include those terms as well. And, to be consistent with our existing convention of expressing time, those terms should also be prepended in decreasing order of significance (i.e., year, followed by month, followed by day). Therefore, the General Form that should be used for expressing time is:


followed by the appropriate "AM" or "PM" designation. For example, ten minutes and fifteen seconds past seven o'clock in the evening on September 21st of the year 1984 would be expressed as:

1984:09:21:07:10:15 PM

which could also be equivalently written as any of the following "improper" expressions:

1984:09:21:19:10:15 AM
1984:09:20:31:10:15 PM
1984:09:20:43:10:15 AM
1984:09:19:55:10:15 PM
1984:09:21:18:70:15 AM
1984:09:21:18:69:75 AM
- etc. -

As a last resort in trying to avoid accepting the actual truth about midnight and noon, you might be tempted to suggest: "Well, let's just define midnight as being 12 AM and noon as being 12 PM, since that's what everybody says they are."

The problem with this suggestion is that truth is not determined by popular opinion.* And you cannot change a truth by merely "redefining" it to be something that it isn't.

*For example, there was a time when everyone thought that the earth was located at the center of the universe, and that everything went around the earth. (It was referred to as "The Ptolemaic Theory".) But just because everybody said that the earth was at the center of the universe, it didn't make it actually true in reality.

As an aside, it is a strange trait of humanity: When a society has spent its whole existence exposed to incorrect ways of thinking and then later is shown the correct ways, its first reaction is to deny those new ways and brand them as being wrong! Galileo found this out when he tried to announce his discovery that everything did not go around the Earth. The world was just unwilling to accept his truths, because those truths were contrary to the established ways of thinking (much as are the truths about AM and PM that have been presented in this current essay).

As we've already indicated, the measurement and specification of time are mathematical processes. And you cannot redefine the laws of mathematics (and thereby introduce needless inconsistencies) for the sole purpose of perpetuating former mistakes in reasoning.

(For further discussion about truth and consistency, see Chapter Zero of my book, "Shades of Reality".)


Midnight is twelve PM (or equivalently, zero AM), and that designation of "PM" (or "AM") remains in effect for the entire midnight hour (i.e., until one AM).

Noon is twelve AM (or equivalently, zero PM), and that designation of "AM" (or "PM") remains in effect for the entire noon hour (i.e., until one PM).

At this point, the story about "The Emperor's New Clothes" comes to mind. It's about two weavers who promise an emperor a new suit of clothes that is invisible to anybody who is stupid or incompetent. When the emperor decides to parade in front his subjects, the townsfolk play along with the pretense of seeing his clothes because they don't want to appear stupid. However a little boy recognizes the real truth and cries out, "But he isn't wearing anything at all!"

Now that you know the "naked" truths about 12 AM and 12 PM, what are you going to do? Are you going to openly admit that noon is actually 12 AM and that midnight is actually 12 PM? Or are you going to keep on pretending just the opposite so that you can continue to conform with all of the fools who "pretend" that they don't know any better?

Click Here to Read More Essays by Bob Bishop ("Mr. Logic")

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