Grammatically Correct: The writer's essential guide to punctuation ...

GRAMMATICALLY CORRECT
USE COMMAS TO SET OFF WORDS OR EXPRESSIONS
THAT ARE "INTERRUPTERS"
A sentence may contain some words that interrupt its flow but don't
interfere with its meaning.
Some may be asides; that is, text that is included simply for
emphasis or effect, or as additional commentary.
The meeting was, to say the least, a total fiasco.
The committee is, generally speaking, reluctant to rock the boat.
The rest, as they say, is history.
The contract fell through, by the way.
Ernie's first book of poetry wasn't a resounding success either, remember.
Needless to say, my friend Cassandra's predictions always materialized.
Some may serve to tie in a point with a preceding sentence.
Her resignation, therefore, is inevitable.
In fact, the profits for the second quarter were up slightly.
However, all was not lost.
The more expensive printer, on the other hand, would cost less to
maintain.
Some may contain information that is necessary to the overall
point, but is parenthetical in the sense that you could take it out
without changing the meaning of what is left.
Her lecture on moose calls, he was happy to report, went very well.
His story of being abducted by giant lizards, when I stopped to think about
it, made little sense.
The food she had just eaten as a mid-morning snack, he pointed out, had
been intended to last the week.
In all the above cases, if the parenthetical element were removed,
the sentence would be essentially unchanged: The meeting was a
total fiasco; Her resignation is inevitable; His story of being
abducted by giant lizards made little sense.
Caution: When parenthetical text comes in the middle of a clause,
be sure not to neglect the closing comma. It is a common error to
write sentences such as The meeting was, to say the least a total
fiasco or Her resignation, therefore is inevitable.
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