English Grammar Review
Let's start with some definitions.
o'clock = "of the clock" or "of the 12 numbers evenly distributed in time and on the perimeter of the clock face" (as opposed to o'sundial)
a.m. = "ante meridiem" or "before midday"
p.m. = "post meridiem" or "after midday"
Rule 1: Always use digits with a.m. and p.m.
Mukhtar plans to arrive in Almaty at two p.m.
Mukhtar plans to arrive in Almaty at 2 p.m.
Rule 2: Do not use a.m. or p.m. unless you use digits.
Our engineer entered Kazakhstan this a.m.
Our engineer entered Kazakhstan this morning.
Rule 3: Use a colon, without spaces, to separate hours from minutes.
Irina called the office in Karagandy at 9-45 a.m.
Irina called the office in Karagandy at 9:45 a.m.
Rule 4a: When using o'clock, use digits (1 through 12) when you want to emphasize the time or when you want to make it easy for the reader to quickly comprehend.
The awards banquet will begin at 7 o'clock.
[okay, quickly understood]
Rule 4b: When using o'clock, use words when you want to be more formal.
The awards banquet will begin at seven o'clock.
Rule 5: For absolute clarity, you can use o'clock with additional descriptive words.
The awards banquet will begin at seven o'clock this evening.
[okay, formal, extra clear]
Rule 6: When not using o'clock or a.m. or p.m., it's okay to spell out the time in words. However, quicker comprehension is usually achieved with digits.
call at seven → call at 7:00
[not: call at 7]
ten after seven → 7:10
a quarter past seven → 7:15
seven twenty-five -- 7:25
Module: Special Topics
Course: English Grammar Review