When is a colon recommended or more grammatically correct than a comma or semicolon when used mid sentence?

Question

Please note I am posting as a UK English writer, I point this out as I know there are differences between American and UK grammar guidelines or accepted practices. I would also add that I am asking from a novelist point of view rather than a technical writer.

Ignoring for now, introducing dialogue or lists, do I really need to worry about colons or can I use semicolons when a comma or period does not suit.

Are there any situations, within a sentence, where a colon is really the only recommended solution.

For example, in researching on the internet I came across the following example :-

A dolphin is not fish: it is a warm-blooded mammal.

It seems to me that a semicolon or comma would equally suffice. I am not asking for the correct formatting of this sentence, or for it to be corrected grammatically but rather more generally:-

Are then any such situations, with two independent clauses where a colon is an absolute must, or grammatically preferred over a semicolon, and regarded as better, writing practice.

Thank you

Answer 1

Are then any such situations, with two independent clauses where a colon is an absolute must, or grammatically preferred over a semicolon, and regarded as better, writing practice.

If this is a question resolved by a style guide you adhere to then follow its guidance.

Otherwise, no. It's just about possible to write down the rules where English requires, or forbids, a full stop, exclamation mark or question mark. Wars have been started over how to wield the comma. But there is no consensus at all on semi-colons or colons.

Note that this answer addresses the issue of grammatically preferred and does not address stylistically preferred.

Answer 2

It is not simple but there is a difference between joining things with a colon or a semicolon.

With a colon there is an assumption of general to specific, or idea and explanation. For example, 'He had a stomach pain: it was constipation.'

With a semicolon there is an assumption of causation: it is as though the word 'because' has been substituted by the punctuation mark (though it is not that simple). Consider:

I entered. She left.

I entered; she left.

The first one says two unrelated events happened. The second one says she left because I entered.

What is the difference between the following sentences?

Henry is a good student: he always pays attention.
Henry is a good student; he always pays attention.

The first defines a good student as one who pays attention. The second says he is a good student because he pays attention. The difference is subtle but real.

Try these examples:

Our problem is simple: Mark made a mistake.
Our problem is simple; Mark made a mistake.

The first one means the problem is a mistake made by Mark. Maybe he ordered three coffees and there are four of them. The second is saying the difficulty is simple because of Mark’s mistake. Instead of it being a really complicated situation, like Mark said it was, it’s actually easily resolved. The two sentences are not the same.

Some people say you shouldn't use either colons or semicolons in fiction. My guess is they are people who don't know how to use them well. I think you should use every tool in your box. A carpenter uses a spokeshave when it is the best tool. Why shouldn't I use a colon?