[Bill Ridgeway]

I've only just spotted this thread so apologies in advance if this is
irrelevant or duplicated.

Hart's Rules (for compositors and readers at the University Press Oxford) is
a reference for such issues.

It states "The semicolon separates two or more clauses which are of more or
less equal importance and are linked as a pair or series" and goes on to
give examples. In all examples the semicolon is followed by a lower case
letter.

It also states "Whereas the semicolon links equal or balanced clauses, the
colon generally marks a step forward, from introduction to main theme, from
cause to effect, premiss sic to conclusion, etc." and goes on to give
examples. In all examples the colon is followed by an upper case letter.

I hope that clarifies the issue.

Regards.

Bill Ridgeway