The Grammary link provided by
@Eva Darrington is the only source we have for now. However, it is a very good one because that page actually cites other sources, including multiple style guides.
From the Grammar article I gathered the following:
If the colon does
not introduce a full sentence, the word after the colon should generally be lowercase. In that situation, capitalizing after the colon is incorrect regardless style guide or British English vs American English.
If the colon
does introduce a single full sentence (but not two full sentences), capitalizing after the colon is optional and differs between style guides.
If the colon introduces two full explanatory sentences following the colon, then capitalization after the colon is required (regardless of style guide or British English vs American English).
To example on the previous examples, here are some examples illustrating the rules as I have paraphrased them:
- Correct: The box included the following: a pen, a pencil, and an eraser.
- Incorrect: The box included the following: A pen, a pencil, and an eraser.
- Correct: The box included the following: everything on the list of needed supplies.
- Incorrect: The box included the following: Everything on the list of needed supplies.
- Correct (depending on style guide): I couldn't believe my eyes: The house was painted purple.
- Also Correct (depending on style guide): I couldn't believe my eyes: the house was painted purple.
- Correct: Maggie wears a brimmed cap at all times: Strong light often gives her a headache. She also likes the way it looks.
- Incorrect: Maggie wears a brimmed cap at all times: strong light often gives her a headache. She also likes the way it looks.
When writing or editing in a context that requires adhering to specific style guide or specific country's vernacular, watch out for the two marked "depending on style". What's correct accordingly one style guide will be incorrect according to one style guide, as well as vice versa.
Please correct me if I am wrong!
This like so many topics in this forum illustrates the significant advantage of what we are doing with International Grammar Forum: We are finding the cut-and-dry strict rules that don't vary between style guides or country. Style guides can be very bad about marking things as "optional" so to speak, which causes a lot of problems in society in many different contexts. What is a matter of recommend style (according to that one style guide) gets mixed up with what is a strict universal grammar error. It could because a student is having their GPA reduced by a teacher who marks things as errors that are a matter of style (without specifying to the student that a certain style guide is required). That is just one example of the many ways grammar rules are hard to understand and often misunderstood because of style guides and other alleged rules that vary by country.
Maybe one day we can take all that we have learned and developed in this forum to make and publish an intentionally lenient OnlineBookClub.org style guide which lets those read it easily learn the relatively set grammar rules that do not vary between style guides or region but without the metaphorical poison of style-specific rules that are usually included with style guides and then falsely learned by some as being more absolute and universal rules than they are. It would be shorter and less strict than other style guides and much easier to use and follow. I think as technology and the internet more and more connects us across the world and makes publishing more independent and decentralized (think the opposite of the APA and thus the APA-style-gude), I think the need for a new type of lenient style guide of this proposed hypothetical kind is going to become more and more needed. What do you all think?
"That virtue we appreciate is as much ours as another's. We see so much only as we possess." - Henry David Thoreau
"Non ignara mali miseris succurrere disco." Virgil, The Aeneid
