Semicolons before conjunctions

Semicolons can be used before conjunctions (words like "and", "but" and "or"), particularly when there are other commas present.

1. When a sentence contains commas, it is possible to use a semicolon before a co-ordinate conjunction to outrank the other commas in the sentence.

Examples:

In fact, rather surprisingly, the majestic pike is hardly used in cooking today; but in Victorian times, pastry-topped pike was a very common dish.

(Semicolon used before "but" to outrank the other commas in the sentence)

          semicolon used before but to outrank
                 the other commas (correct usage)
                               (magazine article)

As the Dutch captain wrote the order banning the killing of the dodos, his sailorshad the last one in their sights; and, as the muskets sounded, dodos were gone forever.

(semicolon before "and")

Shakespeare, a great dramatist, wrote a great many plays; and he wrote a
number of sonnets too.

CO-ORDINATE CONJUNCTION?

Words like "and", "but" and "or" are called "Conjunctions". Sometimes (as in the examples below), they join two sentences together to form one. When conjunctions are used in this way, they are called "co-ordinate conjunctions" and should be preceded by a comma.

She cannot abide tennis, but she loves watching golf.

(Sentence 1: "She cannot abide tennis".
Sentence 2: "She loves watching golf.")
("but" merges two sentences - comma required)

I may consider your plan, or I may stick with mine.

("or" - co-ordinate conjunction - comma required)

Note: The word "co-ordinate" just means "of equal rank". In these sentences, both halves are considered to be the same rank (i.e. they are both full sentences).

OLD FASHIONED?

You do not have to use a semicolon; a comma will suffice. Many people consider it old fashioned to use a semicolon before a co-ordinate conjunction.

Associated lessons:

What are conjunctions?
Conjunctions and commas
Conjunctions and semicolons
Using semicolons before transitional phrases (e.g. however)
Using semicolons in lists
Using semicolons to extend a sentence