The poem’s title, “Mutability,” reveals its pressing theme—change, or more specifically, the unpredictability of human nature. Mutability means liable to change, and Shelley’s poem centers on how human nature is invariably in flux. In the first two stanzas, Shelley confronts the theme of change through similes. First, he compares humans to clouds. The clouds “speed and gleam and quiver” (Line 2). After night comes, “they are lost for ever” (Line 4). He then compares humans to “forgotten lyres” (Line 5). The feeble musical instrument is unreliable and makes a different sound each time someone plays it. Humans are like lyres and clouds because their feelings, thoughts, and bodies come and go, and they are liable to do something dissimilar each encounter.

In Stanza 3, Shelley highlights the theme of change through direct declarations about the human experience. A person’s rest can transform into trouble due to a bad dream. Awake, a person’s “wandering thought” (Line 10) might change their day from good to bad. The list of human behaviors in Lines 11-12 is volatile and furthers the theme that human nature revolves around change. Whatever a person feels, thinks, or does, “its departure still is free” (Line 14). That is, nothing is preventing the emotion or thought from going away.