William said, "Good morning"; but, "Hello," was Henry's greeting.
But: He introduced the man as "my distinguished friend."
116. Use the comma to set off adverbs and adverbial phrases; such as, however, then, also, for example, so to speak, etc.
Such a man, however, can seldom be found.
This sentence, for example, can be improved by changing the order.
117. Use the comma whenever for any reason there is any distinct pause in the sentence that is not otherwise indicated by punctuation, or whenever something clearly is omitted.
We want students, not boys who simply come to school.
Cæsar had his Brutus; Charles the First, his Cromwell; ...
The Semicolon (;)
118. Use the semicolon to separate the clauses of a compound sentence that are long or that are not joined by conjunctions.