A line of reasoning that presents the opposite side of the author’s argument is called a
A line of reasoning that presents the opposite side of the authors argument is called a counter argument
the correct answer should be a counterargument. The opposite side would be whatever the opposing, or countering, argument is. For example, if someone is in support of free college, they would support their argument and perhaps include some information about the counterargument, which would be not supporting free college. Hope this helps.