Colons and semicolons can be helpful when used correctly. Sadly, they are often sprinkled throughout MSS without any regard for sentence construction.

I wish authors would use commas and full stops wherever they can. Only when these fail to convey the full meaning, and the need arises for a supporting phrase should they introduce semicolons or colons.

A phrase that is an additional connecting thought to a sentence already written can be separated from it with either a semi colon, if it is itself a sentence, or a colon if it is not.

For instance…

She brought the clothes in from the washing line; they were dry.
She brought the clothes in from the washing line: dry or not.