ABSTRACT
A colon formally introduces a list or other information that in some way further characterizes or expands upon the text that immediately precedes it. A colon can also introduce supplemental information, quotations, salutations, subtitles, and dialogue; and a colon can separate data. A colon can be followed by a word, series of words, phrase, independent clause, or several independent clauses (sentences). A sentence structured around a colon flags the attention of the reader because it promises more to come, but not before a staged pause (the colon) and a metaphorical drum roll. The colon is particularly effective for formally emphasizing bold statements and pointed questions.
A dash (also known as an em dash), which differs from a hyphen and an en dash, similarly allows for the expansion of ideas, but in different ways. Dashes can be used to emphasize parenthetical information, including abrupt changes in thought; complete the meaning of a sentence; introduce lists; and make certain punctuation-rich sentences easier to read. They can also show interrupted speech, format special cases of source attribution, and signify missing letters and words. Thoughts set off by dashes, especially by double dashes, are arresting because the dash-text-dash structure briefly stops, starts, and stops the reader.
