Via this column, we'll explore one grammar rule each week. If you have a grammar question you'd like me to address, please drop me a line at grace.lavigne@prnewswire.com and I'll do my best to answer it.

This week, Sherlock Holmes and I will use step-by-step logic and deductive reasoning to get to the bottom of the infernal case of the semicolon. Grammar is afoot!

If a comma represents a brief pause, and a period represents a complete stop, then semicolons represent a moderate pause.

Semicolons are used in two main environments:

1. Semicolons can act as "super commas," which are used to separate units of a list when one or more of the units contain commas:

• Holmes found three clues: footprints, which were outside the door; a pistol, which was still loaded; and papers, which smelled of cyanide.
• The murderer visited three cities: Liverpool, England; Paisley, Scotland; and Lusaka, Zambia.

2. Semicolons can also be used to connect clauses:

Use a semicolon in place of a period to connect or form a bond between two statements (typically related or contrasting thoughts) where the conjunction has been left out:

• Professor Moriarty is a criminal mastermind; he is the "Napoleon of Crime."
• Watson received his medical degree in 1878; he is a surgeon.

Use a semicolon before transitional phrases or conjunctive adverbs that connect two clauses (like however, therefore, that is, namely, of course, for example, thus):

• The copper-haired girl was hired as a governess; however, she was unknowingly posing as her employer's daughter.
• One sister died with a shout of "It was the speckled band"; of course, Holmes knew she was referring to a swamp adder.

But don't use semicolons before simple conjunctions (words like but, and, or, nor, for, so, yet):

• Watson led from behind, but never gets the credit he deserves.
• Holmes had a brother named Mycroft and he was more brilliant than Holmes himself.

Optional: You may use a semicolon between two clauses when one has internal punctuation, or in other words, if one or more commas appear in the first or second clause:

• If Holmes can, he will give up cocaine; and if Watson can see it through, they will solve mysteries again.
• When Arthur Conan Doyle started writing the Sherlock Holmes short stories, he created the field of criminology; however, at the time, he never thought he was changing the world.

Semicolons are *always* placed outside of quotation marks. But check out Dear Gracie: Commas/Periods Inside or Outside of Quotation Marks? on the rules for periods and commas.