In a society, man has the power to control the population and food through preventative checks which balance the high birth rate caused by the poor and the amount of available sustenance. Preventative checks are man's way to control the population through abstinence or limiting the number of children that a family can have, whereas positive checks are caused by nature. Some examples of positive checks include diseases or natural disasters. Thomas Malthus suggests that when the rate of human reproduction is left unchecked, it increases in a geometrical ratio. On the other hand, food only increases in an arithmetical ratio, much slower than the population grows. Malthus believes that the reason for a disturbance in the balance between food and population is caused by the poor having multiple children without considering their poverty. He argues that without these kinds of checks the population of the lower class will continue to grow until there is not enough sustenance left to support a society. He says that the poor will often blame the upper class and the government for their low financial status, only adding to the problem as they are not taking any responsibility for their large families. It is for these reasons that Malthus believes preventative population checks should be enforced on a society, therefore preventing the growing imbalance between food resources and the number of people.