A madman is lunatic, insane, someone who suffers from mental disorders. A genius is quite the opposite and not to be confused with an idiot savant. A genius is someone with extraordinary mental powers and high aptitudes. You say that if one gives an answer alluding to "a fine line" between the two that it's "rubbish" but that is not so. There have been people who have slipped from genius to madman over time and those who were perceived to be madmen who turned out to be geniuses. A member of the first category being someone like Vincent Van Gogh or Ludwig Van Beethoven and the latter being someone like Immunologist, Paul Ehrlich or Louis Pasteur, who discovered the cures for Syphilis, Sleeping Sickness, Anthrax, Rabies and proved that disease causing microorganisms were at the core of all illness and death. Before Ehrlich and Pasteur, no doctor washed his hands or made his instruments clean and sanitary which accounted for the many deaths from child bed fever. Their contemporaries, all renowned physicians, thought them madmen...but they were most certainly not. Both were geniuses.
