In the early 20th century, Pierre Berger described how Blake's views echo Mary Wollstonecraft's celebration of joyful authentic love rather than love born of duty, the former being the true measure of purity. Irene Langridge notes that "in Blake's mysterious and unorthodox creed the doctrine of free love was something Blake wanted for the edification of 'the soul'." Michael Davis's 1977 book "William Blake a New Kind of Man" suggests that Blake thought jealousy separates man from the divine unity, condemning him to a frozen death.