Use a semi-colon to separate independent clauses closely related in a thought:

Amherst has a good reputation; many educators rank it high in their list of American colleges.

But don't use a semi-colon when linking clauses with and, but, or yet:

Amherst's Women's Week comes in March and Mount Holyoke's comes in April.

The semi-colon also connects items in a list:

For breakfast we had kippers; strange-looking pink sausage; cereal with raisins, nuts, and marshmallows; and, to finish off, yesterday's prune Danish.

Note that the list consists of phrases, and that one of the phrases ("cereal with raisins, nuts, and marshmallows") itself requires commas. The semi-colon makes it clear which ingredients belong to which larger item.

The semi-colon has a glamorous air of "the professional writer" about it, and often inspires writers to load up their prose with them. Avoid "semi-colonitis," a disease of the prose passage infecting every sentence. Try to restrict yourself to one semi-colon for short paragraphs, two for long ones. Break this rule if absolutely necessary.

Colons Usage

Use the colon as you might use a little arrow, to point up a quotation or a question, or to signal a list or a key point in an argument. A colon takes you from an idea to an illustration:

She liked studying three things: math for its exactness, biology for its complexity, and music for its beauty.

Many writers kept insisting: how could America be a democracy if its founders owned slaves?

   Sentence Fragments
   Comma Splices
   Run-on Sentences
   Dangling or Misplaced Modifiers
   Subject-Verb Agreement
   Split Infinitives
   Which, That, It, and Of
   Semi-colons and Colons
   Apostrophes
   His and Her