Punctuation is intended to clarify the meaning of writing. It provides the key to the logic of an argument; for example, when readers see a semicolon in a work, they know the writer is linking closely related ideas. The ability to use different forms of punctuation to express ideas gives variety, coherence, and strength to writing.
Use a period to end sentences that are statements, indirect questions, or mild commands. Also use a period after most abbreviations and within decimal numbers and amounts of money.
Use a Period With:
The mayor's speech was unusually well received.
The meeting was amicable and important.
An indirect question reports what a person has asked, but not in the speaker's original words. Since the question is paraphrased, quotation marks are not used.
He asked me when the train will leave the station.
She wanted to know whether the supplies would be back in stock by Tuesday.
If you cannot decide whether to use a period or an exclamation mark after a command, use a period. Exclamation marks are used infrequently in formal writing.
Read the next two chapters before Tuesday.
Please leave your muddy shoes on the mat outside the door.
H. Sammis & Sons, Inc., recently issued its annual report.
A. L. Smith just returned from a convention at the U.S. Department of Agriculture.
When a sentence ends with an abbreviation, use only one period.
The meeting will begin promptly at 8 A.M.
I will send your files to Jeffrey Mallack, M.D.
Also note that the official two-letter postal zip code state abbreviations do not use periods. Acronyms—abbreviations formed from the first letters of the words in a name—never use periods.
Within Decimal Numbers and Amounts of Money
A sales tax of 7.5 percent is leveled on all clothing in this state.
He spent $44.50 on the shirt, $36.99 on the pants, and $22.00 on the tie.
Use a question mark to end a sentence, clause, phrase, or single word that asks a direct question. Also use a question mark within parentheses to indicate uncertainty about the correctness of a number or date included within the sentence.
Use a Question Mark
To Indicate a Question
Who invited him to the party?
"Is something the matter?" she asked.
Whom shall we elect? Murray? Harris?
To Indicate Doubt about Information
Socrates was born in 470 (?) B.C.
The codex dates back to A.D. 500 (?)
Use an exclamation point to end a sentence, clause, phrase, or single word that expresses strong emotion, such as surprise, command, and admiration.
Use an Exclamation Mark to Express:
What a week this has been!
Stated above with examples.