Final answer:
In Sonnet 31, Sidney uses the moon as a metaphor for constancy and steadfastness.
Step-by-step explanation:
In Sonnet 31, Sidney uses the moon metaphorically to convey the idea of constancy and steadfastness. The moon is often associated with stability, as it consistently appears in the sky night after night. By using the moon in his sonnet, Sidney suggests that his love for the subject of the poem is unwavering and enduring, just like the moon's presence in the night sky.
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