Subsection 2.3.2 AM an PM
a.m. and p.m. are abbreviations of the Latin phrases ante meridiem and post meridiem.Meridiem refers the time when the sun is directly overhead, in other words, noon, while ante and post translate as before and after, so these terms literally mean “before noon” and “after noon.”
Note that noon is neither a.m. nor p.m. because noon can never be before or after itself. You can say “12:00 noon” but this is a bit redundant; “noon” communicates all that is needed.
Midnight is problematic: What is meant by midnight Friday? It could mean either 12:00 a.m. or 12:00 p.m., depending on whether you consider midnight to be the beginning or ending of the day. This is why watch bills take effect at 12:01 a.m. and why airline flights leave at 11:59 p.m. or 12:01 a.m. but not midnight.
This confusion can also be avoided by using military time, as described in the next section.
