Colons are used in three ways: (1) to illustrate a point, (2) when using subtext in titles, and (3) when introducing a list (such as has been done in presenting these three points) or the introduction in a letter [Dear Sir:].
Example of illustrating a point: “The Hunger Games” is a very popular movie: It was sold out everywhere I went.
Example of illustrating a subtext: “The Solar System: Earth and Beyond”
Example of illustrating a list: I like all kinds of chocolates: milk, dark and white.
Semicolons are used when the difference between two separate statements is being emphasized. Some refer to the semicolon as the “super comma” as it can be used in place of a comma to give more emphasis. Generally there is a joining word used in conjunction with the semicolon. (Conjunction words such as: however, otherwise, therefore, subsequently and in addition to.) It is important to remember that the sentence before the semicolon and the sentence after the semicolon are each complete independent sentences. If one is not, then a semicolon should not be used.
Example: Mark has no problem spending money on specialty cars; however, he is a tight wad when it comes to buying furniture.
There are two sentences here, i.e., “Mark has no problem spending money on specialty cars,” and “He is a tight wad when it comes to buying furniture.” The two sentences are joined by the conjunction word “however.” The first sentence is ended with the semicolon followed by a conjunction (however) and a pause (comma) and, finally, the second sentence.
Semicolons can also be used in place of a comma when providing a list. For example, the sentence given above, “I like all kinds of chocolates: milk, dark and white,” could also be written as, “I like all kinds of chocolates: milk; dark and white. Using either a comma or semicolon is correct and is dependent upon how the writer wants to express themselves.