COORDINATING CONJUNCTIONS (A comma precedes a coordinating conjunction that separates two independent clauses--complete sentences.) Preferably, a writer should not begin a sentence with a coordinating conjunction.
and nor
but or
for so
yet
CONJUNCTIVE ADVERBS a.k.a. ADVERBIAL CONNECTIVES, LOGICAL CONNECTIVES AND SENTENCE ADVERBS (A semicolon separates two independent clauses that are connected by a conjunctive adverb; usually a comma follows the adverb.) If these conjunctive adverbs serve as sentence interrupters, they should be set off from the sentence with commas.
accordingly in fact on the other hand
besides later otherwise
consequently moreover perhaps
finally nevertheless still
furthermore next then
however nonetheless therefore
indeed now
SUBORDINATING CONJUNCTIONS (These connect dependent or subordinate clauses with independent clauses.) NOTE: a subordinate clause without an independent clause is a fragment.
The following conjunctions introduce adverb clauses:
(Introductory adverb clauses should be followed by a comma.)
after because so that whenever
although before though while
as even though till wherever
as if if unless whereas
as long as in order that until
as soon as since when
The following conjunctions can introduce adjective clauses:
(Punctuation is determined by whether the clause is essential or non-essential.)
when which*
where whoever
why whomever
who* whose*
whom* that*
*Also known as relative pronouns
The following conjunctions can introduce noun clauses (No comma(s) required):
where what
why whatever
how whoever
who whomever
whom that
whose
CORRELATIVE CONJUNCTIONS
either . . . or
neither . . . nor
not only . . . but also
both . . . and
whether . . . or
