William Blake's Songs of Innocence (1789) and Songs of Experience (1794), each containing a version of "The Chimney Sweeper," are grounded in Blake's mystical belief system in which the spiritual (innocent) world is separate from the physical (experience) world. In practical terms, because Blake is fundamentally a social critic and reformer--and he sees much in British society in need of reform--he uses the child chimney sweep as the vehicle for his criticism because the use of children as sweeps in the late 18thC. was under scrutiny by British social and political institutions. The two versions of "The Chimney Sweeper" are different only in tone, not in the condemnation of an inhumane practice, and must be looked at side-by-side to understand how they provide a balanced understanding of Blake's view.
In Songs of Innocence, "The Chimney Sweeper" recounts being sold by his father into the chimney-sweeping fraternity before he could even talk:
And my father sold me while yet my tongue/Could scarcely cry 'weep!' 'weep!' 'weep'! 'weep'!/So your chimneys I sweep, and in soot I sleep. (ll. 1-3)
Blake's chimney sweep has, in effect, been sold into a kind of slavery, a startling image when we consider that slavery had been abolished in Britain nearly 50 years before. Blake's point, of course, is that this slavery is both evil and invisible: although there are no chains binding the child sweep, he has been betrayed into a life of suffering ("in soot I sleep") by his father, a parent who has violated the most fundamental of parental responsibilities--to protect his child.
The saving grace, if one can call it that, for the child sweep is his ability to live vicariously in an innocent world through the dream state. The narrator notes that Tom Dacre, who cries because his head has been shaved, thereby making it easier for him to work inside chimneys, escapes his grim world by dreaming:
And by came an angel who had a bright key,/And he opened the coffins [that is, the chimneys) and set them all free;/Then down a green plain leaping, laughing, they run./And wash in a river, and shine in the sun. (ll. 12-16)
This dream state (or spiritual) state gives these enslaved children the freedom that is theirs in a just and spiritually correct world: they are free, playing joyously, clean, and exposed to the sun instead of the darkness and soot within the chimney.
The poem's last stanza, however, in which Tom awakes and returns to his chimney sweeping, ends on a troubling note:
Though the morning was cold, Tom was happy and warm;/So if all do their duty they need not fear harm. (23-24)
The narrator's implication is that--despite the horrific conditions under which Tom and his fellow children work--carrying out their sweeping is a duty (in the real world) that will ultimately set them free, a dubious conclusion given the work that these children perform.
The tone of "The Chimney Sweeper" in Songs of Experience is much harsher, more desperate, and more fatalistic than the tone of the first version. The child sweep identifies himself as
A little black thing among the snow,/Crying 'weep!' 'weep' in notes of woe! . . . They [his parents, who are gone] clothed me in the clothes of death,/And taught me to sing the notes of woe. (ll. 1-8)
In the world of experience, the child sweep is fully aware of his deadly situation, and his language is reminiscent of Blake's poem "London" (part of Songs of Experience) in which the narrator sees on every face "marks of weakness, marks of woe."
Unfortunately for the child sweep of the Songs of Experience, even though he attempts to be a child--"I am happy and dance and sing"--his parents have condemned him to a horrible existence because, like the father in Songs of Experience, they have abandoned their child:
And are gone to praise God and his priest and king,/Who make a heaven of our misery. (ll. 11-12)
The real world in which this child lives and works--governed by parents, organized religion, and political authority--have condemned the child to a life of misery because the child is performing a useful (that is, useful to the world of experience) function.
The two poems, then, both condemn the society in which cruelty passes for duty, but in the world of innocence, there is the possibility of release in the form of dreams; in the world of experience, dreams are not possible and the child sweep's future is misery.