Why is Aristotle referred to in discussions of democracy?
The debate on forms of government has interested man since the times of ancient Greece. It is there, between the fifth and fourth centuries BC, that the first philosophers began to reflect on the subject, effectively creating the foundations of Western political thought. The classifications of the forms of government that have most survived the centuries are those of Plato and Aristotle. Both understood that the government could be of one, of a few or of many, and both theorized that, for each of these possibilities, there was a good and a corrupt form.
Aristotle, a pupil of Plato, will perfect the classification of constitutions made by his teacher by creating the most important work of antiquity on the subject: "Politica".
He studied in detail the different forms of government of the different polis and divided them on the basis of the number of rulers: monarchy, aristocracy and polythéia.
The degenerate forms are tyranny, oligarchy and democracy.
But what is the criterion you used to classify good and corrupt forms?
The former are those in which the rulers act for the common good, the latter those in which they are moved only by personal ends.
For example, it is when the sovereign no longer feels bound by the laws and breaks them for his convenience that the monarchy becomes tyranny.
Oligarchy means precisely "government of the rich", which is very different from the aristocracy, that is, the "government of the best". In the first case, the few rule to increase their wealth, in the second they make their wisdom available to the polis. Similarly, while politéia means "government of the many", democracy here means "government of the people", that is, of the poor, who for Aristotle would use power only for their own interest.
However, we must consider that the democracy that the ancient Greeks had in mind was not the one we are used to, but the one in which citizens, gathered in assembly, concretely took decisions. It was a direct democracy, while ours is representative: we do not take decisions directly, but we elect representatives who do it for us.