The theme of "nothing in life is permanent" in Edgar Allan Poe's "A Dream Within a Dream" can be best supported by the lines:
"All that we see or seem / Is but a dream within a dream."
These lines encapsulate the notion that our experiences and perceptions may not be as concrete or enduring as they appear, highlighting the ephemeral nature of reality. Additionally, the lines:
"Yet if hope has flown away / In a night or in a day, / Is it therefore the less gone?"
These lines also reinforce this theme, as they reflect on the fleetingness of hope and how quickly things can change, emphasizing the idea that nothing is permanent. Together, these lines articulate the poem's exploration of the transient nature of existence.