Use of a period [ . ]

PUNCTUATION -- Use of a period [ . ] -- The Question Mark [ ? ] -- The Exclamation Mark [ ! ]

The Colon [ : ] -- The Semicolon [ ; ] -- The Hyphen [ - ] --The Dash [ — ] -- The Parentheses [ ( ) ]

The Bracket [ [ ] ] -- The Ellipsis [ … ] -- The Apostrophe [ ’ ] -- Quotation marks [ “ ” ]

The Slash or Virgule [ / ] -- Rules for Comma Usage [ , ]

Use a period [ . ] at the end of a sentence that makes a statement. There is no space between the last letter and the period. Use one space between the period and the first letter of the next sentence. This goes against the grain for people using the typography instilled by generations of old-fashioned typewriter users, but modern word-processors nicely accommodate the spacing after a period, and double-spacing after a period can only serve to discombobulate the good intentions of one's software.

If one is using a mono-space font (like Courier) to reproduce the effect of an old-fashioned typewriter, then using a double space after a period would, indeed, be a good idea. This might be useful to remember if one's e-mail client uses Courier, but usually e-mail fonts are determined by the receiver's e-mail program, so Courier is apt to be translated into another font like Times New Roman or Geneva anyway.

See Quotation Marks and Parentheses for special placement considerations with those marks.

Use a period at the end of a command.

• Hand in the poster essays no later than noon on Friday.
• In case of tremors, leave the building immediately.

Use a period at the end of an indirect question.

• The teacher asked why Maria had left out the easy exercises.
• My father used to wonder why Egbert's ears were so big.

Use a period with abbreviations:

Dr. Espinoza arrived from Washington, D.C., at 6 p.m.

Notice that when the period ending the abbreviation comes at the end of a sentence, it will also suffice to end the sentence. On the other hand, when an abbreviation ends a question or exclamation, it is appropriate to add a question mark or exclamation mark after the abbreviation-ending period:

Did you enjoy living in Washington, D.C.?

Occasionally, a statement will end with a question. When that happens, it is appropriate to end the sentence with a question mark.

• We can get to Boston quicker, can't we, if we take the interstate?
• His question was, can we end this statement with a question mark?
• She ended her remarks with a resounding why not?