Do you remember from high school algebra (or even junior high algebra) how you learned about positive numbers and negative numbers? I do. In that class my first-year algebra teacher drew a long horizontal line on the board and put a mark at the center. That mark he labeled “0.” That is, zero. Then he wrote the numbers 1, 2, 3, and so on as far as he could to the right of the zero, and he wrote the same numbers to the left. The numbers to the right were positive numbers, +1, +2, +3, and so on, and the numbers to the left were negative, -1, -2, -3, etc., etc. But what about the zero sitting there in the middle? Is zero positive or negative? Most of the students in my class didn’t know and couldn’t answer. But zero is neither, the teacher emphasized. It’s right in the middle. It doesn’t have any sign. It can’t have a sign; it doesn’t really exist. There’s nothing there. It’s zero, after all.
Likewise, in writing I’ve seen a lot of people use the term “12 AM” or “12 PM.” This is as ridiculous as trying to label zero as “positive” or “negative.” I’ve always been confused as to what, for example, “12 AM” means. Does it mean midnight or noon? It could be either. Does the “AM” refer to the twelve-hour period that precedes the 12, or follows it? Twelve o’clock is neither AM or PM. It’s like zero, it’s not one or the other. Granted, a point in time called “12 o’clock” does exist, and twice a day too, unlike zero which means “nothing at all.” But 12 o’clock is at the boundary between the AM and the PM states. Like zero, it is neither one nor the other.
I’ve noticed a general (and strictly unofficial) convention emerging to use “12 AM” as noon, and “12 PM” for midnight, (at least I think that’s what other writers are saying) but both of these are still incorrect, and give the wrong impression. I hope we can nip this convention in the bud, and get back to using “Noon” and “Midnight” in their correct positions.