Semicolons and Colons

Semicolons

The semicolon is stronger than a comma but weaker than a period. While it can be used (at times) in lieu of a comma, its primary role is closer to that of a period. Its most common use is between two independent clauses (complete sentences) not joined by a conjunction.

Semicolons may be used within dialogue. There is no rule to support otherwise (at least that I have found so far). Also note that the clause that follows the semicolon is not capitalized, with the exception of proper nouns, of course.

Before an Adverb

The following adverbs, among others, should be preceded by a semicolon when the adverb is used transitionally between two independent clauses (complete sentences): then, however, thus, hence, indeed, accordingly, besides, and therefore.

• Then: She received her acceptance letter; then, she began packing.
• However: I didn't like where the conversation was going; however, he was right.
• Indeed: He didn't begin feeling ill until after the examination; indeed, that was very fortunate.

"I think, therefore I am" (Descartes) remains an exception to this rule.

Before a Conjunction

An independent clause (complete sentence) introduced by a conjunction may be preceded by a semicolon, especially when the independent clause has internal punctuation.

• The professor spied the class suspiciously; yet by the time he looked up, the class had conveniently returned to their work.
• Quietly, he strode down the hallways, intent upon the capture of the wayward students; but Fate was against him this evening, as was typical of his luck as of late, and they had conveniently disappeared.

In a Series

When items in a series involve internal punctuation, it is less confusing to use semicolons to separate the items instead of commas.

• He made note of the items he still needed to get: Boomslang skin, which was needed to replace that which had been stolen; chamomile stalks, a special order for Madam Pomfrey; and Bubotuber pus, which Neville had very conveniently dumped all over his robes.

With "that is" and the Like

A semicolon may be used before expressions such as that is or namely.

• We really needed to get our priorities straight; that is, he did.

With Parentheses or Brackets

Semicolons always follow the closing parentheses or bracket.

• I found the book in the dirty laundry pile (very unexpectedly); then, I reshelved it.

Colons

In a Series

A colon introduces an element or a series of elements that describe what precedes the colon. Between independent clauses (complete sentences), it functions much like a semicolon though more strongly emphasizes sequence. It can be used in leiu of a period to introduce a series of related sentences.

• Hogwarts is made up of four houses: Slytherin, Gryffindor, Ravenclaw, and Hufflepuff.
• Many of the professors held a second job: four of them even tutored failing students in subjects different than what they taught.
• She was faced with a terrible dilemma: Should she ignore the incessant banging on her door? Should she open it and face the insulting words he would no doubt be aiming in her direction? Or should she jinx him and run?

Capitalization After a Colon

When a colon is used within a sentence, like in the first two examples above, the first word following it is lowercased unless it is a proper name. When a colon introduces two or more sentences, like the third example above, or introduces a speech in dialogue or an extract, the first word following it is capitalized.

However, when the (complete) sentence following a colon is lengthy and distinctly different from what precedes the colon, it is often capitalized.

• She saw the enemy slowly approaching, and only one word came to mind: "Run!" (dialogue)
• Neville: I don't know what happened! (extract)
• The situation was critical: In no way could they teach the entire school all the defense hexes and spells they needed to know in time in order to fight the enemy when they arrived on the last day of term.

With "as Follows" and the Like

A colon is normally used after as follows, the following, and similar expressions.

• The steps are as follows: chop the ingredients, toss them into the cauldron, and stir.

With Parentheses or Brackets

Colons always follow the closing parentheses or bracket.

• A calm stole over the two wizards (Snape and Malfoy): they knew this was going to be the end.

Inappopriate Use of Colons

Never use a colon after expressions such as namely, for example, and the like.

Never use a colon before a series introduced by a preposition.

• The examination was concerned with Potions, Divination and Arithmancy, all his least favorite subjects.