When Keats experiences feelings of fear (1) that he may die before he has written the volumes of poetry that he is convinced he is capable of writing, (2) that he may never write a long metrical romance, fragments of which float through his mind, and (3) that he may never again see a certain woman and so never experience the raptures of passionate love — then he feels that he is alone in the world and that love and fame are worthless.
In "When I Have Fears," Keats turns to the Shakespearean sonnet with its abab, cdcd, efef, gg rhyme scheme and its division into three quatrains and a concluding couplet. It was written after Keats made a close study of Shakespeare's songs and sonnets and, in its development, it imitates closely one of Shakespeare s own sonnet patterns. The three quatrains are subordinate clauses dependent on the word "when"; the concluding couplet is introduced by the word "then." The sonnet, like "On First Looking into Chapman's Homer," is constructed with care. Like "Chapman's Homer," it is concerned with the subject of poetry, to which Keats adds another favorite theme, that of love.
The sonnet is distinguished by Keats' characteristic melodiousness and by his very distinctive style, which is marked by the presence of archaic words borrowed from the Elizabethan poets. The first line, "When I have fears that I may cease to be," appeals at once to the ear and is a compelling invitation to the reader to go on with the poem. "Before high-piled books, in charact'ry, / Hold like rich garners the full-ripen'd grain" contains two words, charact'ry and garners, that are quite remote from the kind of language recommended by Wordsworth in his famous preface to the second edition of Lyrical Ballads and quite remote from the language used by Keats in conversation with his friends.
"When I Have Fears" is a very personal confession of an emotion that intruded itself into the fabric of Keats' existence from at least 1816 on, the fear of an early death. The fact that both his parents were short-lived may account for the presence of this disturbing fear. In the poem, the existence of this fear annihilates both the poet's fame, which Keats ardently longed for, and the love that is so important in his poetry and in his life. As it happened, Keats was cheated by death of enjoying the fame that his poetry eventually gained for him and of marrying Fanny Brawne, the woman he loved so passionately. This fact gives the poem a pathos that helps to single it out from among the more than sixty sonnets Keats wrote. The "fair creature of an hour" that Keats addresses in the poem was probably a beautiful woman Keats had seen in Vauxhall Gardens, an amusement park, in 1814. Keats makes her into an archetype of feminine loveliness, an embodiment of Venus, and she remained in his memory for several years; in 1818, he addressed to her the sonnet "To a Lady Seen for a Few Moments at Vauxhall." "When I Have Fears" was written the same year. One of his earliest poems, "Fill for Me a Brimming Bowl," written in 1814, also concerns this lovely lady. In the poem, he promises that "even so for ever shall she be / The Halo of my Memory."