The Aesthetic is Kierkegaard's thought is the first part of his three stages of life or three spheres of existence. Kierkegaard defines the aesthetic as an essentially hedonistic way of life. In aesthetics Kierkegaard does not mean fine arts or even beauty. He appeals to the ancient origin of the words according to which aesthetic is everything which is perceived by the senses. The aesthetic in Kierkegaard's view, therefore, is everything which has to do with the senses, especially their pleasure.
The aesthetic for Kierkegaard has several levels, ranging from sexual lust to the passion of enjoying the arts. The aesthetic person lives in material life and does not attempt to transcend them. He seeks no awareness or reflection of his human condition. Aesthetics does not involve morals (the ethical) nor faith (the religious). The only guideline of the aesthetic person in Kierkegaard's view is his own gratification of physical needs, reminiscent of Freud's "Pleasure Principle". Aesthetic decisions are made according to urges with no broader context, and without any moral "good" or "bad".
The Aesthetic for Kierkegaard is lowest form of human life, under the higher ethical and religious life of faith. For a broader discussion see our article on Kierkegaard: The Aesthetic, Ethical and Religious or our summary of Fear and Trembling.