Shelley's 'A Defence of Poetry' is a rejoinder to Love Peacock's charges levelled against poetry and poets in his four Ages of Poetry. Peacock called poets 'semi-barbarians in a civilized community' and condemned Shelley's own poetry as "querulous egotistical rhapsodies."
Defending poetry, Shelley says that poetry is on embodiment of "beautiful idealism of moral excellence." The poet "excites a generous impulse, an ardent thirst for excellence." He calls the poet a nightingale , who sits in darkness and sings to cheer its own solitude, with sweet sound." He says that poetry is the creative impulse in man. Poets are "not only the authors of language and of music, of the dance and architecture, and statutory, and painting, they are the institutors of laws, and founders of a civil society, and the inventors of the arts of life." They are men of the most spotless virtue, the most consummate prudence, the most fortunate of men." They are "philosophers of the very loftiest power." Poetry is the record of the best and happiest moments of the happiest and best minds."
Poetry is 'the centre and circumference of knowledge and it comprehends all science.' Consequently, Shelley calls the poets "unacknowledged legislators of the world." The poet reveals 'those forms which are common to universal nature and existence.' Hence a poem is "the very image of life expressed in its eternal truth."
Thus "a poet, as he is the author of the highest wisdom, pleasure virtue and glory, so he ought personally to be the happiest, the best the wisest and the most illustrious of men." So the poet is the legislator of the moral, spiritual and intellectual life in the world.