5.2 Sentence capitals
Capitalize the first letter of a word that begins a sentence, or the first of a set of words used as a sentence:
This had the makings of a disaster. Never mind.
Come on. Tell me!
Sylvie replied, ‘She’s a good girl.’
I thought, ‘There goes my theory.’
The question is, does anyone have an antidote?
Quoted single words or phrases that do not constitute a sentence are not capitalized:
He’d say ‘bye’ and run down the wide school steps
Certain young wines do not ‘travel well’
For a full discussion of quotation marks and the punctuation that accompanies them see
In British English, matter following a colon begins with a lower-case initial, unless it is a displayed quotation or extract, but in US style a capital letter may be used after a colon if it introduces a complete sentence.