Grammar

Uses of the Comma	*Examples:*
After a long introductory phrase.	For a brief period some years ago, New Westminster was the capital of BC.
To prevent the misreading of a sentence.	They left at 5:00 p.m., for Calgary was still a long way off.
To mark off short interrupting phrases.	He was, in fact, born in Halifax.
Between long coordinate clauses, especially when they are joined by "but", "and", or "or".	He thought they lived in Red Deer, but actually it was Edmonton.
In a series of adjectives after a linking verb, use a comma after each term but the last.	The cowboy was tall, lean, and dark haired.

To join two parts of a balanced sentence.

Example:
Mining is the chief industry in the Kootenays; lumbering the chief industry in the Cariboo.

The root word of "the" is "this", or "that" (definite)
The root word of "a/an" is "any" (indefinite)