punctuation - When should one use the comma versus the semicolon, and vice versa?

I cannot understand the difference between the comma and semicolon. Can you please clarify?

Answer

From eHow:

Comma (,)

1) Use a comma to separate 2 independent clauses joined by a coordinating conjunction such as and, but and or. The key here is to have 2 subject verb pairs.

Example: The students reviewed for the exam, and the teacher corrected the term papers.

In this example we have 2 subject verb pairs: "students reviewed" and "teacher corrected."

Example: The teacher corrected the papers and entered the grades in the grade book.

In this example we use the coordinating conjunction "and" but have 1 subject and 2 verbs: "teacher corrected, entered"; therefore, no comma is used.

2) Use a comma to separate items in a series to avoid ambiguous meaning.

Example: Uncle willed me his property, houses, and warehouses.

In this example, we mean that uncle willed me 3 items--his houses, warehouses, and property.

Example: Uncle willed me his property, houses and warehouses.

In this example, we mean that uncle willed me 2 items--all his property, which consisted of houses and warehouses.

3) Use a comma with introductory elements such as subordinating clauses that come at the beginning of the sentence.

Example: Because the river had flooded, the school closed for the week.

The introductory element, or subordinating clause is "because the river had flooded." It is introduced with the subordinating conjunction "because."

Example: The school closed for the week because the river had flooded.

In this example the subordinating clause is at the end of the sentence so we do not use a comma.

Semicolon (;)

1) Use a semicolon to separate 2 independent clauses in a sentence, closely related, with no coordinating conjunction.

Example: The students reviewed for the exam; the teacher corrected the papers.

Example: The candidates spoke to the crowds during Election Day; each candidate spoke passionately about the fate of the country.

2) Use a semicolon to separate items in a series where the series themselves contain commas.

Example: We visited our relatives in Albany, NY; Philadelphia, PA; and Washington, D.C.