 Scholars such as David Herlihy and Michael Postan use the term Malthusian limit to express and explain some tragedies as resulting from overpopulation.In his 1798 "Essay on the Principle of Population", Thomas Malthus asserted that eventually humans would reproduce so greatly that they would go beyond the limits of necessary resources; once they reach this point, catastrophe becomes inevitable.In his book, "The Black Death and the Transformation of the West", professor David Herlihy explores this idea of plague as an inevitable crisis imposed on humanity to control the population and human resources.