From the beginning of the article:
It is one of the frustrations of the historian of ancient Greece that we know so little about the internal functioning of the Greek city-states in the Classical period. We have, to be sure, plenty of information on the operation of the Athenian democracy; still, we neither know how typical the Athenian model was for other democracies, nor how widespread democracy was elsewhere in the Greek world. The situation is considerably worse in the case of oligarchies. Even though it is possible that they were much more numerous in the Classical Greek world than democracies, the lack of coherent literary sources reduces our knowledge to scraps, which have to be gleaned from stray remarks, often made by hostile Athenians. It is remarkable, for example, that only one statement favorable to oligarchy has come down to us from Classical Greek antiquity.
In view of that, it seems to me worth while to attempt to take stock of what is known about oligarchy and of the place it occupied among other Greek constitutions. Much of the material I cite will be familiar, but some, I hope, will be novel enough to shed a new light on the problem.
The ancient Greeks attributed none of the three types of government which they identified and bequeathed to us – monarchy, oligarchy, and democracy – to one of the great lawgivers of the Archaic age. True enough, later generations would call Solon the “father of the democracy” realizing that without his political and economic reforms the “democracy” they knew in the fifth and fourth centuries BC could never have come into being. But this label could only be attached in retrospect: there is not a speck of evidence that Solon himself or his contemporaries envisaged the system of government he created at the dawn of sixth-century Athens as a democracy.