 Locke is now in a position to explain the function of a legitimate government and distinguish it from illegitimate government. The aim of such a legitimate government is to preserve, so far as possible, the rights to life, liberty, health and property of its citizens, and to prosecute and punish those of its citizens who violate the rights of others and to pursue the public good even where this may conflict with the rights of individuals. In doing this it provides something unavailable in the state of nature, an impartial judge to determine the severity of the crime, and to set a punishment proportionate to the crime. This is one of the main reasons why civil society is an improvement on the state of nature. An illegitimate government will fail to protect the rights to life, liberty, health and property of its subjects, and in the worst cases, such an illegitimate government will claim to be able to violate the rights of its subjects, that is it will claim to have despotic power over its subjects. Since Locke is arguing against the position of Sir Robert Filmer who held that patriarchal power and political power are the same, and that in effect these amount to despotic power, Locke is at pains to distinguish these three forms of power, and to show that they are not equivalent. Thus at the beginning of chapter 15 “Of Paternal, Political and Despotic Power Considered Together” he writes: