 The structure of the Course explains why the law of the three stages (which is often the only thing known about Comte) is stated twice. Properly speaking, the law belongs to dynamic sociology or theory of social progress, and this is why it serves as an introduction to the long history lessons in the fifth and sixth volumes. But it equally serves as an introduction to the work as a whole, to the extent that its author considers this law the best way to explain what positive philosophy is.