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

PUNCTUATION
Exception
If a parenthetical word or expression doesn't break the continuity
of the sentence, it is sometimes acceptable to omit the commas
altogether. If you are uncertain whether or not to include commas,
say the sentence aloud, spontaneously, and decide if a pause sounds
right.
She did in fact pay the loan back.
The course in my opinion is a joke.
IF A SUBJECT IS FOLLOWED BY A NONRESTRICTIVE DESCRIPTOR,
USE COMMAS TO SET OFF THE DESCRIPTOR. IF IT IS FOLLOWED
BY A RESTRICTIVE DESCRIPTOR, DO NOT USE COMMAS
When an element that either follows or lies within an independent
clause provides some information about the subject of that clause,
this information may be considered either restrictive or nonrestrictive.
A restrictive element acts to identify precisely which subject,
out of various possible ones, is being discussed. A nonrestrictive
element, while it adds more information about the subject, does not
serve to further identify it-in this case, the subject is already fully
identified. (Some authorities call these relationships defining and
nondejining, or limiting and nonlimiting. The meaning is the
same.)
A nonrestrictive element is parenthetical in the sense that it is
not critical to the meaning of the sentence; if it were removed, the
meaning of what remained would still be intact. In contrast, if a
restrictive element were removed, meaning would be lost.
Compare the following two sentences:
By two in the morning, the only people still at Shirley's party were her
oldest friend, Susan, and her neighbor George.
By two in the morning, the only people still at Shirley's party were her
friend Susan and her upstairs neighbor, George.
In case A, the name Susan is nonrestrictive, since by definition
one can have no more than one oldest friend. The inclusion of
Susan is adding more information about this friend-her namebut
omitting it wouldn't introduce any ambiguity as to which friend
is meant. In contrast, George serves to identify which neighbor was
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