Final answer:
In Sonnet 43, the single idea developed throughout the poem is the speaker's unending and unconditional love. In The Song of Wandering Aengus, the speaker is more hopeful about getting what he is longing for.
Step-by-step explanation:
In Sonnet 43 by Elizabeth Barrett Browning, the single idea that is developed throughout the poem is the unending and unconditional love of the speaker for their beloved. This idea is expressed through lines such as: "I love thee to the depth and breadth and height My soul can reach" and "I love thee to the level of every day's Most quiet need, by sun and candle-light". These lines emphasize the vastness and intensity of the speaker's love.
In the poem "The Song of Wandering Aengus" by W.B. Yeats, the speaker is more hopeful about getting what he is longing for. Evidence to support this can be found in lines such as: "I will find out where she has gone, And kiss her lips and take her hands; And walk among long dappled grass". These lines show the speaker's determination and hopefulness in finding the person he is longing for.