COLONS AND SEMI-COLONS
Colons
Use the colon after the salutation in a business letter. You should also use a colon at the end of a sentence or phrase introducing a list or (sometimes) a quotation.
Our study included the three most critical problems: insufficient capital, incompetent management, and inappropriate location.
A colon should not be used when the list, quotation, or idea is a direct object of the verb or preposition. This rule applies whether the list is set off or run in.
Another way you can use a colon is to separate the main clause and another sentence element when the second explains, illustrates, or amplifies the first.
Management was unprepared for the union representatives’ demands: this fact alone accounts for their arguing well into the night.
Semi-colons
Use a semicolon to separate two closely related independent clauses.
The outline for the report is due within a week; the report itself is due at the end of the month.
A semicolon should also be used instead of a comma when the items in a series have commas within them.
Our previous meetings were on November 11, 2006; February 20, 2007; and April 28, 2008.
Use a semicolon to separate independent clauses when the second one begins with a conjunctive adverb such as however, therefore, or nevertheless or a phrase such as for example or in that case.
Our supplier has been out of part D712 for 10 weeks; however, we have found another source that can ship the part right away.