Published in 1843, Søren Kierkegaard's 'Either/Or' is a seminal work in existential philosophy that explores the complexities of human choice and the nature of existence. Kierkegaard distinguishes between the aesthetic and ethical stages of life, emphasizing the importance of personal responsibility and the 'leap of faith' in the pursuit of truth. This work laid the groundwork for modern existentialism and continues to influence philosophical thought on individuality and moral decision-making.

Søren Kierkegaard's 'Either/Or' laid the groundwork for existentialism, introducing themes of spiritual dread, isolation, and radical choice that permeated 20th-century religious and modernist poetry. Poets like Rainer Maria Rilke and Wallace Stevens engaged with these existential dilemmas, exploring the complexities of human existence.