The earliest classification of constitutions was the work of Aristotle.
Aristotle in his politics had a lot to say about constitution. He was quite able to differentiate between two kinds of rules: ruble by passion, that is rules by men of desire and caprice; and rules by reason. He clearly remarked that the former is not a good government due to men's not a good government due to men's selfish interest and passion.
He said that a society will think of good government if such a government is governed by reason that is laws.