Elaboration and Explanation
The colon is mainly a mark of introduction: It signals that the words following will explain or amplify the meaning of the preceding clause.
A colon is always preceded by a complete main clause—one containing a subject and predicate and not starting with a subordinating word.
Be aware of a common mistake that arises when using a colon to join two clauses: If the information following the colon would be a complete sentence on its own, it must begin with a capital letter.
- Hydrology has a deceptively simple definition: the study of water.
- A more precise definition might be the following: the study of the movement of water on or over land, its flows and gathers, its evaporations and condensations, its interactions with landforms like deltas and coastlines.
- Canada has one salient feature: namely, the longest coastline.
- The plot is founded on deception: The protagonist has a secret identity.
- The test was in three minutes: I had to run to class.
- The evidence could only mean one thing: The butler was guilty.
A colon can also be used to introduce a list of items but not if the list is grammatically essential to the wording of the sentence.
- Incorrect: The three assigned topics for your essay on Infinite Jest are: tennis, lenses, and mathematics.
- Correct: These are the three assigned topics for your essay on Infinite Jest: tennis, lenses, and mathematics.
- The musicology syllabus includes three genres: jazz, blues, and hip-hop.
- Canada has long coastal boundaries on three oceans: the Pacific, the Arctic, and the Atlantic.
- There are three types of people in the world: those who can count and those who can’t.
- In the drawer I found two things: a letter and a yellow notebook.