Patrick studied all night, that's why he got an A on the exam
Would this sentence need a semicolon after night?
***** NOT A TEACHER *****
Ms. Wainwright,
(1) Because I am old-fashioned (and old), your sentence does not
"work" for me. And I think it would not work for some stricter teachers.
(2) If you wanted to use a comma, I think that you would have to include
a conjunction:
Patrick studied all night,
so that's why he got an A on the exam.
(NOTE: Maybe some super strict teachers would tell you that the
words "that's why" are not really necessary.)
(3) I think that a semicolon -- as you said -- would also be correct:
Patrick studied all night; he got an A on the exam.
(NOTE: See how much smoother and "dramatic" it is without "that's
why")?
(4) And, of course, you would be correct if you wrote:
Patrick studied all night. That's why he got an A on the exam.
Patrick studied all night. He got an A on the exam.
(5) Personally, I favor the sentence with
so.
***** NOT A TEACHER *****