Use a period to close sentences that make statements or give mild commands.
All books are either dreams or swords.
—AMY LOWELL
Don’t use a fancy word if a simpler word will do.
—GEORGE ORWELL, “Politics and the English Language”
A period also closes indirect questions, which report rather than ask questions.
I asked how old the child was.
We all wonder who will win the election.
Until recently, periods have been used with most abbreviations (see Chapter 61) in American English. However, more and more abbreviations are appearing without periods.
| Mr. | MD | BC or B.C. |
| Ms. | PhD | BCE or B.C.E. |
| Mrs. | MBA | AD or A.D. |
| Dr. | RN | AM or a.m. |
| Jr. | Sen. | PM or p.m. |
Some abbreviations rarely if ever appear with periods. These include the postal abbreviations of state names, such as FL and TN (though the traditional abbreviations, such as Fla. and Tenn., do call for periods), and most groups of initials (MLA, CIA, AIDS, UNICEF). If you are not sure whether a particular abbreviation should include periods, check a dictionary or follow the style guidelines (such as those of the Modern Language Association) you are using in a research project.