When to use the semicolon
The semicolon is one of the least common punctuation marks, but it is a useful one. Semicolons are sometimes used instead of full stops. They are used to separate two clauses that are grammatically independent but have related meanings.
Uses of the semicolon
The semicolon is used to separate lengthy coordinate clauses where the coordinate conjunction is omitted.
The sky was dark; the rain fell in torrents; the road was deep in mud; the way was long; the weary travelers plodded on in silence.
The semicolon is also used to separate two clauses connected by a transitional adverb. Examples of such connectors are: nevertheless, however, nonetheless, therefore, otherwise etc.
I was not impressed with the show; nevertheless, I watched it.
She was not feeling well; however, she went to work.
Susie was not feeling well; therefore, she decided to take a day off work.
I hope the snow clears; otherwise, we will have to cancel the picnic.
Note that the full stop is also possible in the sentences given above.
I hope the snow clears. Otherwise, we will have to cancel the picnic.
Note that commas are not usually possible in cases where the semicolon is used.
A comma can separate two coordinate clauses connected by a coordinating conjunction.
Tom is doing well, and it should be obvious that he must go to university. (BUT NOT Tom is doing well, it should be obvious that he must go to university.)
Commas are not possible in the absence of a coordinating conjunction.
Semicolons are also used to separate items in a list.