Aristotle was speaking in terms of what convinces people. This is only his 'Rhetoric' however. His 'Logic' deals with correct arguments.
However, I do think that there are cases where an ad hominem is correct however. If someone's argument is based on his own authority, and his authority is widely acknowledged, then the only way to attack the argument is to attack the arguer. One example is the repeated misuse of Einstein as an authority om things like economics or theology.
However, I do think that there are cases where an ad hominem is correct however. If someone's argument is based on his own authority, and his authority is widely acknowledged, then the only way to attack the argument is to attack the arguer. One example is the repeated misuse of Einstein as an authority om things like economics or theology.