Both a.m. and p.m., two Latin abbreviations for time indication, are known to be confusing. The former, shortened from ‘ante meridiem,’ starts from midnight to before midday. Meanwhile, the latter, ‘post meridiem,’ starts from midday to before midnight.
The word ‘meridiem’ is usually misspelled as ‘meridian,’ which comes from ‘meridian line.’
Nonetheless, what is not less perplexing is the way we choose which of them to use in indicating the points of time around midnight and midday.
In short, from midnight to 0:59 o’clock, it’s 12:00 a.m. to 12:59 a.m. This time period is the most confusing.
From 1:00 o’clock to 11:59 o’clock, it’s 1:00 a.m. to 11:59 a.m.
Meanwhile, from noon/midday to 12:59 o’clock, it’s 12:00 p.m. to 12:59 p.m. This time period is also confusing.
From 13:00 o’clock to 23.59 o’clock, it’s 1:00 p.m. to 11:59 p.m.
Moreover, there are different ways to write each of the abbreviations.
The first and most common way is written in lowercase with two periods following: ‘a.m.’ and ‘p.m.’
The next way is to use capital letters with a smaller font size, with or without periods: ‘A.M.’ and ‘P.M.’, and ‘AM’ and ‘PM.’
Not only Thais get confused with this issue. Among native speakers, there have been many campaigns calling for the cancellation of both abbreviations.