Shelley possessed two remarkable qualities of intellect -- a brilliant imagination, and a logical exactness of reason. His inclinations led him (he fancied) almost alike to poetry and metaphysical discussions. I say 'he fancied,' because I believe the former to have been paramount, and that it would have gained the mastery even had he struggled against it. However, he said that he deliberated at one time whether he should dedicate himself to poetry or metaphysics; and, resolving on the former, he educated himself for it, discarding in a great measure his philosophical pursuits, and engaging himself in the study of the poets of Greece, Italy, and England. To these may be added a constant perusal of portions of the Old Testament -- the Psalms, the Book of job, the Prophet Isaiah, and others, the sublime poetry of which filled him with delight.
As a poet, his intellect and compositions were powerfully influenced by exterior circumstances, and especially by his place of abode. He was very fond of travelling, and ill-health increased this restlessness. The sufferings occasioned by a cold English winter made him pine, especially when our colder spring arrived, for a more genial climate. In 1816 he again visited Switzerland, and rented a house on the banks of the Lake of Geneva; and many a day, in cloud or sunshine, was passed alone in his boat -- sailing as the wind listed, or weltering on the calm waters. The majestic aspect of Nature ministered such thoughts as he afterwards enwove in verse. His lines on the Bridge of the Arve ["Mont Blanc"], and his Hymn to Intellectual Beauty, were written at this time. Perhaps during this summer his genius was checked by association with another poet [Byron] whose nature was utterly dissimilar to his own, yet who, in the poem he wrote at that time [Childe Harold's Pilgrimage, Canto 3], gave tokens that he shared for a period the more abstract and etherealised inspiration of Shelley. The saddest events awaited his return to England [the suicides of Fanny Godwin and especially of Harriet Shelley]; but such was his fear to wound the feelings of others that he never expressed the anguish he felt, and seldom gave vent to the indignation roused by the persecutions he underwent; while the course of deep unexpressed passion, and the sense of injury, engendered the desire to embody themselves in forms defecated of all the weakness and evil which cling to real life.
He chose therefore for his hero a youth nourished in dreams of liberty, some of whose actions are in direct opposition to the opinions of the world; but who is animated throughout by an ardent love of virtue, and a resolution to confer the boons of political and intellectual freedom on his fellow-creatures. He created for this youth a woman such as he delighted to imagine -- full of enthusiasm for the same objects; and they both, with will unvarnished, and the deepest sense of the justice of their cause, met adversity and death. There exists in this poem a memorial of a friend of his youth. The character of the old man who liberates Laon from his tower-prison, and tends on him in sickness, is founded on that of Doctor Lind, who, when Shelley was at Eton, had often stood by to befriend and support him, and whose name he never mentioned without love and veneration.
During the year 1817 we were established at Marlow in Buckinghamshire. Shelley's choice of abode was fixed chiefly by this town being at no great distance from London, and its neighbourhood to the Thames. The poem was written in his boat, as it floated under the beech-groves of Bisham, or during wanderings in the neighbouring country, which is distinguished for peculiar beauty. The chalk hills break into cliffs that overhang the Thames, or form valleys clothed with beech; the wilder portion of the country is rendered beautiful by exuberant vegetation; and the cultivated part is peculiarly fertile. With all this wealth of Nature which, either in the form of gentlemen's parks or soil dedicated to agriculture, flourishes around, Marlow was inhabited (I hope it is altered now) by a very poor population. The women are lacemakers, and lose their health by sedentary labour, for which they were very ill paid. The Poor-laws ground to the dust not only the paupers, but those who had risen just above that state, and were obliged to pay poor-rates. The changes produced by peace following a long war, and a bad harvest, brought with them the most heart-rending evils to the poor. Shelley afforded what alleviation he could. In the winter, while bringing out his poem, he had a severe attack of ophthalmia, caught while visiting the poor cottages. I mention these things -- for this minute and active sympathy with his fellow-creatures gives a thousandfold interest to his speculations, and stamps with reality his pleadings for the human race.
The poem, bold in its opinions and uncompromising in their expression, met with many censurers, not only among those who allow of no virtue but such as supports the cause they espouse, but even among those whose opinions were similar to his own. I extract a portion of a letter written in answer to one of these friends [Godwin]. It best details the impulses of Shelley's mind, and his motives: it was written with entire unreserve; and is therefore a precious monument of his own opinion of his powers, of the purity of his designs, and the ardour with which he clung, in adversity and through the valley of the shadow of death, to views from which he believed the permanent happiness of mankind must eventually spring.
'Marlow, Dec. 11, 1817.
'I have read and considered all that you say about my general powers, and the particular instance of the poem in which I have attempted to develop them. Nothing can be more satisfactory to me than the interest which your admonitions express. But I think you are mistaken in some points with regard to the peculiar nature of my powers, whatever be their amount. I listened with deference and self-suspicion to your censures of The Revolt of Islam; but the productions of mine which you commend hold a very low place in my own esteem; and this reassured me, in some degree at least. The poem was produced by a series of thoughts which filled my mind with unbounded and sustained enthusiasm. I felt the precariousness of my life, and I engaged in this task, resolved to leave some record of myself. Much of what the volume contains was written with the same feeling -- as real, though not so prophetic -- as the communications of a dying man. I never presumed indeed to consider it anything approaching to faultless; but, when I consider contemporary productions of the same apparent pretensions, I own I was filled with confidence. I felt that it was in many respects a genuine picture of my own mind. I felt that the sentiments were true, not assumed. And in this have I long believed that my power consists; in sympathy, and that part of the imaginatiom which relates to sentiment and contemplation. I am formed, if for anything not in common with the herd of mankind, to apprehend minute and remote distinctions of feeling, whether relative to external nature or the living beings which surround us, and to communicate the conceptions which result from considering either the moral or the material universe as a whole. Of course, I believe these faculties, which perhaps comprehend all that is sublime in man, to exist very imperfectly in my own mind. But, when you advert to my Chancery-paper, a cold, forced, unimpassioned, insignificant piece of cramped and cautious argument, and to the little scrap about [Godwin's novel] Mandeville which expressed my feelings indeed, but cost scarcely two minutes' thought to express, as specimens of my powers more favourable than that which grew as it were from "the agony and bloody sweat" of intellectual travail; surely I must feel that, in some manner, either I am mistaken in believing that I have any talent at all, or you in the selection of the specimens of it. Yet, after all, I cannot but be conscious, in much of what I write, of an absence of that tranquillity which is the attribute and accompaniment of power. This feeling alone would make your most kind and wise admonitions, on the subject of the economy of intellectual force, valuable to me. And, if I live, or if I see any trust in coming years, doubt not but that I shall do something, whatever it may be, which a serious and earnest estimate of my powers will suggest to me, and which will be in every respect accommodated to their utmost limits.'