Songs of Innocence and of Experience is a single book made of two facing collections of short lyric poems. Blake's own subtitle calls them poems showing the two contrary states of the human soul, and the work asks to be read as a pair rather than as one mood replacing another.
The Innocence poems are written to sound like children's songs and hymns. An introduction describes a piper who turns his tunes into written verse so every child may joy to hear them. The lamb, the shepherd, the echoing green, laughing children, and a tender protecting God recur, and the world is felt as cared for even when life is hard.
That care is tested rather than naive. The Innocence Chimney-Sweeper tells of a boy sold into soot who comforts himself with a dream of an angel setting the sweepers free, ending on the consoling thought that those who do their duty need not fear harm. The Divine Image places mercy, pity, peace, and love in God and in the human form alike.
The Experience poems revisit the same subjects with a colder eye. London hears mind-forged manacles in every face; The Tiger asks whether the maker of the gentle lamb also forged a creature of fearful symmetry; The Garden of Love finds a chapel and graves where children once played. Holy Thursday and a second Chimney-Sweeper expose the poverty and exploitation that the Innocence songs had softened.
Read together, the two halves form Blake's argument. Neither innocence nor experience is the whole truth: innocence alone is blind to suffering, while experience alone hardens into despair and cruelty. The contrary states illuminate each other, and the reader is left holding both the trust of the child and the knowledge of the adult.