Depending upon the number of people involved in governing and the focus of their interests, Aristotle distinguished six kinds of social structure in three pairs:

what is a constitution? For Aristotle, a constitution or government is the arrangement of powers in a state. Looking at the structure of a household and state, we can assume that man is a political animal for Aristotle and man, by nature, depends on other men. Men require help from each other which is why they desire to live together. Aristotle says “Men cling to life even in the midst of misfortune, seeming to find in it a natural sweetness and happiness.”[1]

The very important point that Aristotle raises here is that the mutual or common interest of men is what brings them together. So one of the purposes of a state is to work as a body that respects the common interests of the citizens that reside there. Hence, it can be said that common interest is what brings people together to help each other. Another definition of Aristotle is one that he gives in chapter 12 where he says that the highest science of all is political science and the good of this science is justice or common sense in other words. Aristotle then moved towards the function of a state. He believed that the function of a state is to ensure supreme good of people, in the moral and intellectual sense. Happiness comes from virtue and it is the ultimate goal of mankind. State is the agency that helps men to achieve their ultimate goal.[2]

…Kingship, aristocracy and constitutional government are the true constitutional forms but they all have perversions that come to being when the rulers of these governments are catering self-interest instead of the common interest. Kingship turns to tyranny when perverted, aristocracy turns to oligarchy and democracy is the perversion of the constitutional government of many. Democracy is the rule of the many poor who work for the interest of the needy while oligarchy is the rule of the few rich that take only their interest in account as rulers. And tyranny, the perversion of monarchy is a constitution formed for the interest of the one tyrannical ruler. Hence, none of these perversions are in common interest of all.[9]

Aristotle rejects oligarchy and democracy on the basis of inequality and a constitution that cannot keep justice is not a true constitution. He says that democracy is only equal in respect to free birth and oligarchy is considered unequal because of wealth. Wealth and birth are not enough to determine equality; the element of moral and intellectual virtue is what these constitutions do not promote at all.[10] Aristotle thinks equality is an important element as it stabilizes a constitution.

A state with only one ruler is either a monarchy or a tyrrany;
A state with several rulers is either an aristocracy or an oligarchy; and
A state in which all rule is either a polity or a democracy.All monarchies become tyrannies, all aristocracies become oligarchies, and all republics/polities become democracy (mob rule). History is clear on the corrupting nature of power, especially within government.
Of course we live in such a government. However, we have a nice mixture of all 3 corrupt forms of government.
Executive Branch = tyrant
SCOTUS = oligarchs
House/Senate = mob
At this point, the three different forms trade corruption and evil amongst each other, at the expense of the populace.