mm wrote:
I'll tell you how I remmeber this, and how I think it arose. The
moment of noon is neither before noon or after noon, but the
59.999999999...... seconds after that are after noon, and yet still
part of the minute that is 12:00. (and part of the second that is
12:00:00.) So even though all but the tiniest bit of the minute is not
noon, most of 12:00 noon is PM.

I'll have to admit that makes a lot of sense. The time exactly one
minute after noon is 12:01PM. If noon has to be called either 12:00PM
or 12:00AM, then out of the two, 12:00PM is the much more logical
choice since it would be wacky for 12:00AM to be followed immediately
by 12:01PM.

However, it is still not very good terminology since (a) the literal
meaning of "12:00AM" is nonsensical and (b) there is already a
perfectly good word ("noon") to describe the concept. On the other
other hand, it is convenient for digital clocks to be able to read
"12:00PM" instead of "noon", which is a good argument for defining
12:00PM to be noon. On the other other other hand, there are various
authorities whose opinions should matter, and they don't seem to all
agree on any one thing.

- Logan