When certain adverbs are pulled out to the front of a sentence and are used to form a bridge -- that is, show a relationship -- between two sentences, they become conjunctions which we call conjunctive adverbs. Some of them are
moreover, however, nevertheless, therefore, consequently
thus, hence, yet, still, then, so
(Here is where I would make the argument that so and yet are not coordinate conjunctions. They are adverbs that are, when they are out in the front of a sentence, used to connect two sentences. We call these conjunctive adverbs.)
Conjunctive adverbs connect two independent sentences and take a period or semicolon in front of them and a comma after if they have more than one syllable.
...He arrived very late; therefore, he was not included in the discussion.
...She was also in the car; however, she was not injured.
...The surgery was scheduled for Friday; still we knew there could be a last-minute glitch.
...We turned left at the intersection; then we proceeded with caution down the narrow lane.
To be continued...
Happy punctuating!
Margie