I finished a book on the French philosopher Auguste Compte written by his friend John Stuart Mill. Compte is called (by wikipedia) the "first philosopher of science," and with what Mill describes as a genius mind, Compte envisioned subjects of knowledge evolving through three stages of understanding: 1) theological -- stuff happens because God makes it happen. 2) metaphysical -- stuff happens because of the essence of things -- heavy things fall because their heaviness causes it, and 3) positivism -- patterns in events and antecedents need not be related to casual agents, the patterns are all that is important.
Mills also comments on Compte's later works where Compte goes...well...a bit nuts. He imagines a human religion with leaders deciding right ways of thinking, a society of imposed selfless sacrifice, of massive inequality between classes, and meditations to the essence of humanity. He thinks about destroying books that are unacceptable to his religious ideas. Just has weird ideas, like that stuff written on paper should not be thought of as an idea but something existing in space, and colored green. Compte starts to impose on his writing strange systems, such as that the first letter of every paragraph must spell words. His writings have historical inaccuracies unexpected for someone of his education. Mills began the custom of thinking of the "good Compte" based on his earlier works, and the "bad Compte" based on what he wrote later. Probably as Mills was a friend, it would have made him sad that Compte ceased to be as good as he had been previously.