When is a colon used as opposed to a semicolon

A colon is used to introduce explanatory information such as tabulations, lists, etc. It is also used for salutations, (e.g., Dear so-and-so:), in clock time (e.g., 2:15 a.m.), for periodical reference (e.g., 4:3), and between book title and book subtitle (e.g., href="/go/http://www.amazon.com/gp/product/052178512X/sr=1-5/qid=1138055096/ref=sr_1_5/102-8707280-5044124?%5Fencoding=UTF8">Dictionaries: The Art and Craft of Lexicography). A colon is used before a final clause that explains or amplifies something in that sentence, e.g., The dissertation needs work: it lacks flow. A colon introduces a series or summarizing statement, e.g., The following is on our list of places to go: grocery store, toy store, doughnut shop. She had one great love: him. A colon is used in proportions, e.g., 2:1, and as a ratio sign, e.g., 1:2::3:6. A colon may introduce a quotation, especially a long one. Colons go outside quotation marks unless they are part of the quotation itself. A colon also is used to end all paragraphs that introduce a paragraph of quoted material. A colon is used in dialogue text, e.g., Kyle: Do you want to have lunch? Holly: Yes. A colon is used in correspondence for headings and introductory terms (To: From: Re:) and to separate writer/typist and carbon-copy abbreviations from the recipients. A colon can be used to give emphasis, e.g., He had only one hobby: eating. Remember to capitalize the first word after a colon only if it is a proper noun or starts a complete sentence, e.g., Scientists have found a name for the opposite of gravity: levity. The panel consists of: Dr. Juli, Dr. Kipfer, and Dr. Bellantoni. Do not combine a dash and a colon. By contrast, a semicolon is sometimes regarded as a weak period or strong comma and used in ways similar to periods and commas. A semicolon can mark the end of a clause and indicate that a clause following is closely related to the previous clause. A semicolon can also divide a sentence to make the meaning more clear. A semicolon can be translated to mean 'and' or 'but'.