If a sentence is not complete and it is terminated by a period, we have a sentence fragment as in the sentence below.
A period is used to signal the end of a complete sentence.
A period is also used at the end of an indirect question.
Polite requests can be followed either by a period or by a question mark.
A period should be placed after every part of the abbreviation
A.D. | Dr. Watson |
Ave. |
There are six different ways to write ante meridiem (before noon) and post meridiem (after noon)
All caps with periods | 10 A.M., 10 P.M. |
All caps without periods | 10 AM, 10 PM |
Small caps with periods | 10 A.M., 10 P.M. |
Small caps without periods | 10 AM, 10 PM |
Lowercase with periods | 10 a.m., 10 p.m. |
Lowercase without periods | 10 am, 10 pm |
Lower case abbreviations are usually written with periods
i.e. | e.g. |
Very common abbreviations and units of measure do not take periods
mph | mp3 |
rpm | mpg |
Academic degrees can be written with or without periods
DDS | EdD |
M.S. | B.A. |
Government agencies and international organizations are written without periods
FBI | NATO |
EU | UN |