"at last there was a physical proof that something happened when innocence changed into experience."
The original cover of The Songs of Innocence
Public DomainThe original cover of The Songs of Innocence - Credit: William Blake

As well as the work of John Milton (most notably Paradise Lost) Pullman was heavily influenced by William Blake. One of Blake's most famous works is the collection of poems called Songs of Innocence and of Experience.

They were first published and illuminated in 1789 by Blake himself, and remain among his most popular works.

The original cover of The Songs of Experience
Public DomainThe original cover of The Songs of Experience - Credit: William Blake

The Songs are two sets of intertwined, often conflicting poems from the viewpoint of both childhood (innocence) and adulthood (experience). They demonstrate the way the same event can be viewed with completely different meaning depending on the state of the person in question. This is especially true for directly linked poems such as the two Nurse's Songs (one appearing as a song of innocence, the other experience) and Infant Joy and Infant Sorrow.