Semicolons and colons are indeed handy—and actually quite simple to use.
What does a semicolon do?
A semicolon creates a softer break than a period or a stronger pause than a comma. (In fact, it looks like a period stacked on a comma.)
A semicolon’s main job is to connect related sentences into compounds. Instead of using a comma and coordinating conjunction (and, but, or), you can join two sentences with just a semicolon.
Two sentences: I presented the slideshow. My colleague slept through it.
Comma and conjunction: I presented the slideshow, but my colleague slept through it.
Semicolon: I presented the slideshow; my colleague slept through it.
Semicolon: I presented the slideshow; however, my colleague slept through it.
Note that you need a semicolon even when the second clause begins with a conjunctive adverb like however. These “professorial words” (accordingly, besides, consequently, finally, indeed, likewise, meanwhile, moreover, nevertheless, therefore, etc.) must have a semicolon before them and a comma after them when forming a compound sentence.
A semicolon’s other job is to provide a stronger break when commas are already involved.
Confusing list: We need to brainstorm our best ideas, plan, prototype, and test them, and present them to the board.
Sorted with semicolons: We need to brainstorm our best ideas; plan, prototype, and test them; and present them to the board.
Confusing compound: After the board meeting, we will, with the president’s approval, launch design work, and the project managers will address schedules, budgets, and assignments.
Sorted with semicolons: After the board meeting, we will, with the president’s approval, launch design work; and the project managers will address schedules, budgets, and assignments.
What does a colon do?
A colon is an introducer. The material before the colon introduces the material after. You’ve seen colons perform this function in memo and email headings.
To: All Employees
From: Deirdra Reynolds
You’ve also seen colons at the end of salutations, introducing the content of business letters.
Dear President Smith:
In text, a colon follows a complete sentence to introduce a concept, explanation, or formal quotation.
Our mission centers around a single word: hope.
Our hope is not wishful thinking: we actively create a better future.
President Smith summed up his address: “We have hope because we are making the future.”
Note that a complete sentence precedes the colon in each of these examples. Never place a colon between a verb and its object or a preposition and its object.
Incorrect: Our mission creates: hope.
Correct: Our mission creates hope.
Correct: Our mission creates something priceless: hope.
Incorrect: We create the future through: expert planning and teamwork.
Correct: We create the future through expert planning and teamwork.
Correct: We create the future through two strategies: expert planning and teamwork.
You can fix such an error by removing the colon or by adding an object (such as “something priceless” or “two strategies”) before the colon.
If you use a colon to introduce a bulleted or numbered list, make sure the words before the colon form a complete sentence.