In "A Defence of Poetry,” Shelley suggests that thoughts and feelings in life are "always arising unforeseen and departing unbidden.” Which lines from "Mutability” also reflect the idea that life is fleeting? We are as clouds that veil the midnight moon;
How restlessly they speed, and gleam, and quiver
Or like forgotten lyres, whose dissonant strings
Give various response to each varying blast
We rest.—A dream has power to poison sleep;
We rise.—One wandering thought pollutes the day
We feel, conceive or reason, laugh or weep;
Embrace fond woe, or cast our cares away