Søren Kierkegaard's philosophy has been a major influence in the development of 20th century philosophy, especially Existentialism and Postmodernism. Kierkegaard was a 19th century Danish philosopher who has been called the "Father of Existentialism".McGrath, Alister E. The Blackwell Encyclopedia of Modern Christian Thought. Blackwell Publishing, 1993. p 202 His philosophy also influenced the development of existential psychology.Matustik, M. J. and M. Westphal (eds). Kierkegaard in Post/Modernity, Indiana University Press, 1995, ISBN 0253209676

Kierkegaard criticized aspects of the philosophical systems that were brought on by philosophers such as Georg Wilhelm Friedrich Hegel before him and the Danish Hegelians. He was also indirectly influenced by the philosophy of Immanuel Kant.Green, Ronald M. Kierkegaard and Kant: The Hidden Debt. SUNY Press, 1992, ISBN 0791411079 He measured himself against the model of philosophy which he found in Socrates, which aims to draw one's attention not to explanatory systems, but rather to the issue of how one exists.See for example, Concluding Unscientific Postscript to Philosophical Fragments: "Socrates' infinite merit is to have been an existing thinker, not a speculative philosopher who forgets what it means to exist... The infinite merit of the Socratic position was precisely to accentuate the fact that the knower is an existing individual, and that the task of existing is his essential task." Swenson/Lowrie translation (1941), p.184-5.

One of Kierkegaard's recurrent themes is the importance of subjectivity, which has to do with the way people relate themselves to (objective) truths. In Concluding Unscientific Postscript to Philosophical Fragments, he argues that "subjectivity is truth" and "truth is subjectivity." What he means by this is that most essentially, truth is not just a matter of discovering objective facts. While objective facts are important, there is a second and more crucial element of truth, which involves how one relates oneself to those matters of fact. Since how one acts is, from the ethical perspective, more important than any matter of fact, truth is to be found in subjectivity rather than objectivity.Hong, Howard V. and Edna H. "Subjectivity/Objectivity." Søren Kierkegaard's Journals and Papers. Vol. 4. Indiana University Press, 1975, p. 712-13. ISBN 0253182433

Note on pseudonyms

Many of Kierkegaard's earlier works from 1843–1846 were written pseudonymously. In the non-pseudonymous The Point of View of My Work as an Author, he explained that the pseudonymous works are written from perspectives which are not his own: while Kierkegaard himself was a religious author, the pseudonymous authors wrote from points of view that were aesthetic or speculative. One exception to this is "Anti-Climacus", a pseudonymous author developed after the writing of The Point of View. Anti-Climacus is a religious author who writes from a Christian perspective so ideal that Kierkegaard did not wish it to be attributed to himself.Kierkegaard, Søren. Papers and Journals, trans. A. Hannay, London, Penguin Books, 1996.

Because the pseudonymous authors write from perspectives which are not Kierkegaard's own, some of the philosophy mentioned in this article may or may not necessarily reflect Kierkegaard's own beliefs. Just as other philosophers bring up viewpoints in their essays to discuss and criticize them, Kierkegaard assigns pseudonyms to explore a particular viewpoint in-depth, which may take up a whole book or two in some instances, and Kierkegaard, or another pseudonym, critiques that position. For example, the author, Johannes Climacus is not a Christian and he argues from a non-Christian viewpoint. Anti-Climacus, as mentioned earlier, is a Christian to a high degree and he argues from a devout Christian viewpoint. Kierkegaard places his beliefs in-between these two authors.

Most of Kierkegaard's later philosophical and religious writings from 1846–1855 were written and authored by himself, and he assigned no pseudonyms to these works. Subsequently, these works are considered by most scholars to reflect Kierkegaard's own beliefs.Watts, Michael. Kierkegaard. Oneworld, 2003, ISBN 1851683178 Where appropriate, this article will mention the respective author, pseudonymous or not.

Themes in his philosophy Alienation Alienation is a term applied to a wide variety of phenomena including: any feeling of separation from, and discontent with, society; feeling that there is a moral breakdown in society; feelings of powerlessness in the face of the solidity of social institutions; the impersonal, dehumanised nature of large-scale and bureaucratic social organisations. Kierkegaard recognizes and accepts the notion of alienation, although he phrases it and understands it in his own distinctly original terms. For Kierkegaard, the present age is a reflective age—one that values objectivity and thought over action, lip-service to ideals rather than action, discussion over action, publicity and advertising to reality, and fantasy to the real world. For Kierkegaard, the meaning of values has been removed from life, by lack of finding any true and legitimate authority. Instead of falling into any claimed authority, any "literal" sacred book or any other great and lasting voice, self-aware humans must confront an existential uncertainty.

Humanity has lost meaning because the accepted criterion of reality and truth is ambiguous and subjective thought—that which cannot be proved with logic, historical research, or scientific analysis. Humans cannot think our choices in life, we must live them; and even those choices that we often think about become different once life itself enters into the picture. For Kierkegaard, the type of objectivity that a scientist or historian might use misses the point—humans are not motivated and do not find meaning in life through pure objectivity; instead, they find it through passion, desire, and moral and religious commitment. These phenomena are not objectively provable—nor do they come about through any form of analysis of the external world; they come about through inward reflection, a way of looking at one's life that evades objective scrutiny.

Kierkegaard's analysis of the present age uses terms that resemble but are not exactly coincident with Hegel and Marx's theory of alienation.

Abstraction An element of Kierkegaard's critique of modernity in his socio-political work, Two Ages, is the mention of money — which he calls an abstraction.Kierkegaard, Søren. The Two Ages, trans. Howard and Edna Hong. Princeton University Press, ISBN 9780691072265Perkins, Robert L. Two Ages: International Kierkegaard Commentary. Mercer University Press, ISBN 9780865540811 An abstraction is something that only has a reality in an ersatz reality. It is not tangible, and only has meaning within an artificial context, which ultimately serves devious and deceptive purposes. It is a figment of thought that has no concrete reality, neither now nor in the future.

How is money an abstraction? Money gives the illusion that it has a direct relationship to the work that is done. That is, the work one does is worth so much, equals so much money. In reality, however, the work one does is an expression of who one is as a person; it expresses one's goals in life and associated meaning. As a person, the work one performs is supposed to be an external realization of one's relationship to others and to the world. It is one's way of making the world a better place for oneself and for others. What reducing work to a monetary value does is to replace the concrete reality of one's everyday struggles with the world —to give it shape, form and meaning— with an abstraction. Kierkegaard lamented that "a young man today would scarcely envy another his capacities or skill or the love of a beautiful girl or his fame, no, but he would envy him his money. Give me money, the young man will say, and I will be all right."Two Ages, p.75, Hong translation.

Death Death is inevitable and temporally unpredictable. Kierkegaard believed that individuals needed to sincerely and intensely come to realize the truth of that fact in order to live passionately. Kierkegaard accuses society of being in death-denial. Even though people see death all around them and grasp as an objective fact that everyone dies, few people truly understand, subjectively and inwardly, that they will die someday. For example, in Concluding Unscientific Postscript, Kierkegaard notes that people never think to say, "I shall certainly attend your party, but I must make an exception for the contingency that a roof tile happens to blow down and kill me; for in that case, I cannot attend."

Dread or anxiety For Kierkegaard's author, Vigilius Haufniensis, anxiety/dread/angst (depending on the translation and context) is unfocused fear. Haufniensis uses the example of a man standing on the edge of a tall building or cliff. When the man looks over the edge, he experiences a focused fear of falling, but at the same time, the man feels a terrifying impulse to throw himself intentionally off the edge. That experience is anxiety because of our complete freedom to choose to either throw oneself off or to stay put. The mere fact that one has the possibility and freedom to do something, even the most terrifying of possibilities, triggers immense feelings of dread. Haufniensis called this our "dizziness of freedom."

In The Concept of Anxiety, Haufniensis focuses on the first anxiety experienced by man: Adam's choice to eat from God's forbidden tree of knowledge or not. Since the concepts of good and evil did not come into existence before Adam ate the fruit, which is now dubbed original sin, Adam had no concept of good and evil, and did not know that eating from the tree was evil. What he did know was that God told him not to eat from the tree. The anxiety comes from the fact that God's prohibition itself implies that Adam is free and that he could choose to obey God or not. After Adam ate from the tree, sin was born. So, according to Kierkegaard, anxiety precedes sin, and it is anxiety that leads Adam to sin. Haufniensis mentions that anxiety is the presupposition for hereditary sin.

However, Haufniensis mentions that anxiety is a way for humanity to be saved as well. Anxiety informs us of our choices, our self-awareness and personal responsibility, and brings us from a state of un-self-conscious immediacy to self-conscious reflection. (Jean-Paul Sartre calls these terms pre-reflexive consciousness and reflexive consciousness.) An individual becomes truly aware of their potential through the experience of dread. So, anxiety may be a possibility for sin, but anxiety can also be a recognition or realization of one's true identity and freedoms.

Despair