The key word is PARENTHETICAL (that is, unessential to the structure of the sentence):
(Come to think of it,) Alex would probably like you to do his homework.
(Whether Alex studies or not,) he gets good grades.
[But note: Whether Alex studies or not is not my concern. In this case, "Whether Alex studies or not" is all the subject of the sentence.]
Alex would be happy if you did his homework for him (, if you think the teacher won't be able to tell).
Some teachers don't know what to make of Alex (, since he sometimes seems very well prepared).