"Mad Song" is a mimicking of or rebuttal to the six mad songs from Percy’s ‘Tom o’Bedlam’ poems in “Reliques", through which Blake is able to recapture the spirit and simplicity of the Elizabethan pastoral elegy in only a limited series of lyrics. He is also able to act as a pastoral youth poet in this element, focusing on, and praising in full, rural life, purity, innocence, and his beloved.
Plot-wise, it is usually argued that the speaker here is a ghost who is tormented by light (daytime) and therefore only comes out at night and in the darkness. The overall tone or feeling to the poem is of grotesque nature. The voice of the poor, half-witted, cruelly treated vagabond speaker is a horrific cry of misery wrung from his heart. This bode’s well with the image of Blake’s to his contemporaries; that being one of general lunacy and an overly excited imagination that has been ungoverned so long it is now completely ungovernable. Every natural object in the poem is itself attached to some bizarre and wild real-life personification (his notes strike, the day weeps, the tempests play, the earth scorns, clouds are fiends, etc.). For a man who is constantly claiming to vision spirits, ghosts, fiends, and angels lurking in the natural world around him, the personification of nature in this way is absolutely necessary and essential to the expression of his imagination (or lunacy).
The speaker is describing the day—the world of newfound experience. He is aware of his unfortunate inevitability to live within this horrific world where “the earth scorns” for acting upon desire. There is a sense of hope in his voice though, attacking his situation “like a fiend in a cloud with howling woe” with the ambition to live the day up regardless of pain and oppression served, and burst through it’s shackles into the night rather than retreat from it in fear. Although he seems imprisoned in the night’s darkness, the day offers no refuge for him, instead only accenting the limits of the experienced state.
"Mad Song" is one of Blake’s most famous poems outside of “Songs of Innocence and Experience.” Written when Blake was still very young (Blake scholars estimate this was written when he was around the age of fourteen), the poet begins to show signs of his genius and mastering power of personification. “Mad Song” is representative of a very young and brittle poetic mind saturated in the popular modes and styles of the Age of Sensibility on the brink of breaking out.
As commentary, "Mad Song" reflects both the poet and his society. The world in which the speaker lives is oppressive and he has no escape. Less obviously, the speaker is just as guilty for living in this world and being a part of it without creating his own refuge within it to escape to. On this level, Blake is accusing himself of being too idle, and of thus contributing to the overall perpetuation of the experienced terrain.