Blake's theory of contraries was not a belief in opposites but rather a belief that each person reflects the contrary nature of God, and that progression in life is impossible without contraries. Moreover, he explores the contrary nature of reason and of energy, believing that two types of people existed: the "energetic creators" and the "rational organizers", or, as he calls them in The Marriage of Heaven and Hell, the "devils" and "angels". Both are necessary to life according to Blake.[2]