Introduction Existentialism is one of the most extraordinary, most influential, and at the same time, one of the most difficult to define movements in the history of philosophy. It is not a rigid doctrine, a school, or a system; rather, it is a rebellion against all kinds of thought that attempt to confine philosophical systems, abstract concepts, and humanity to a universal essence. At the center of existentialism lies the claim that "the existence of man," that is, the singular, concrete, feeling, anxious, decision-making, and dying individual, precedes all abstract philosophical categories. This movement was born in the mid-19th century from the solitary rebellion of Søren Kierkegaard, a melancholic genius from Denmark, against Hegel's immense philosophical system and the comfort of institutional Christianity; after nearly a century, in the mid-20th century, it transformed into a mass intellectual and cultural movement that spoke to the spirit of war-torn Europe through Jean-Paul Sartre. This narrative will examine this great journey of existentialism within a periodic framework intertwined with the thoughts of its founding figures and the spirit of the age they lived in. 1. Chapter: The Solitary Genius – Søren Kierkegaard and the Birth of Existentialism (1813-1855) Existentialism was born not in a library or a university chair, but in the gloomy streets of 19th century Copenhagen, within the inner world of a man filled with melancholy, irony, and deep faith. Søren Aabye Kierkegaard is one of the most original and disturbing voices of modern philosophy. His entire philosophical project is built upon defending the "existing individual" against Hegel's vast and abstract philosophical system and his followers in Denmark. 1.1. A Rebellion in Hegel's Shadow: To understand Kierkegaard's thought, one must know what he opposed. Georg Wilhelm Friedrich Hegel (1770-1831) was perhaps the last great system builder of Western philosophy. Hegel had constructed a vast philosophical system that viewed all reality as the dialectical process of the "Absolute Spirit" (Geist) revealing itself. In this system, the individual was merely a stop in the great and rational flow of history. In Denmark, Hegelianism had also turned into an official ideology that made Christianity a rational and systematic doctrine, especially in the hands of theologians like Hans Lassen Martensen. Kierkegaard, at this point, launched an unrelenting war against Hegel and his Danish followers. His criticism was based on the following fundamental points: Concrete Individual Against Abstract Man: Hegel's system speaks in abstract terms like "Man" or "Spirit." However, according to Kierkegaard, what is real is not these abstract categories, but the singular individual that exists "here and now," with its hopes, fears, regrets, and passions. In Hegel's grand system, everything is explained, but the living, breathing individual is forgotten. With Kierkegaard's famous irony, the Hegelian philosopher is like a man who explains the whole world but forgets his own address. Freedom and Possibility Against Necessity: For Hegel, history is a necessary and rational process; when we look back at the past, we understand that everything had to be this way. However, for Kierkegaard, human existence is characterized not by necessity, but by possibility, uncertainty, and risk. The future is open, and the individual must make a choice at every moment. This moment of choice is laden with anxiety (angst), as the outcomes of the choice cannot be known in advance, and the individual bears the entire responsibility for this choice alone. 1.2. Stages of Existence and the Radical Choice of "Either/Or": Kierkegaard defined three fundamental "stages of existence" (stadier) that shape human life. These represent different lifestyles and value systems. The transition between these stages is possible not through a rational argument, but through a passionate and irrational "leap" (spring). Kierkegaard's monumental work published in 1843, Either/Or (Enten-Eller), particularly addresses the radical choice between the first two stages. Aesthetic Stage: It is a mode of existence based on experiencing the moment, pleasure, novelty, and sensory experience. The prototype of the aesthetic individual is the "Seductive Johannes" described in the first volume of Either/Or . This individual constantly chases new pleasures but never finds lasting satisfaction. Life is merely a series of fragmented, momentary experiences. The ultimate result of this stage is a feeling of despair and existential meaninglessness (melancholy). According to Kierkegaard, the aesthetic individual has not yet become a "self" (selv); their soul is like a leaf tossed by external stimuli. Ethical Stage: This is the stage the individual enters by choosing themselves upon realizing their despair. The prototype of this stage is Judge Wilhelm from the second volume of Either/Or . The ethical individual takes universal moral laws, social duties, and responsibilities seriously. They commit to the institution of marriage, view their work as a profession (kald), and confront and embrace their past. They understand themselves as a continuous process of becoming, a whole of duties. At this stage, the individual frees themselves from aesthetic chaos and begins to become a "self." However, this is not complete satisfaction; the ethical individual realizes that they can never fully reach the ideal through their own efforts, which leads them to a deep sense of guilt and awareness of sin. Religious Stage: According to Kierkegaard, this is the highest and most authentic stage of human existence. This stage is characterized by the teleological suspension of the ethical, that is, by the absurdity of faith. The most striking example of this stage is given through the story of the prophet Abraham in his work Fear and Trembling (1843). Abraham, by God's command, undertakes an action that is entirely contrary to the universal moral law (the duty of fatherhood), which is to sacrifice his son Isaac. Abraham's action cannot be justified rationally or morally; he enters into an absolute relationship with God in complete solitude, anxiety, and trembling, "by the absurdity of faith." For Kierkegaard, this is the purest example of what faith is: Faith is not a rational acceptance, but a leap in the midst of objective uncertainty, the most passionate form of existence. At this stage, the individual stands before God as a "single individual" (hin Enkelte), under absolute responsibility beyond all universal morals and social rules. 1.3. The Truth of Anxiety, Despair, and Subjectivity: Kierkegaard's contributions to existential psychology are as important as the theory of stages. Anxiety (Angest): In his work titled The Concept of Anxiety published in 1844, he distinguishes anxiety from fear. Fear has a specific object; we are afraid of a snake, an enemy. However, the object of anxiety is uncertain; it is a "fear of nothingness" felt in the face of the dizzying possibility of freedom. Anxiety is the deep distress one feels when looking into the infinite abyss of one's freedom to make a choice. Anxiety is not a curse; rather, it is the greatest indication that a person possesses a soul, is free, and differs from an animal. Despair (Fortvivlelse): In his work titled The Sickness Unto Death published in 1849, he examines despair as a fundamental illness of the human self. According to him, the human self is a synthesis between the finite and the infinite, the temporal and the eternal, necessity and possibility. Failing to establish the balance of this synthesis leads to despair. Misconstructing one's self: getting stuck in one's finite, worldly side (the despair of finitude) or getting lost in fantastic dreams, abstract possibilities (the despair of infinity). However, the deepest form of despair is living without being aware of having a self, that is, living without knowing one is in despair. The only remedy for despair is for the self to reach the end of its own despair and gain a new self by relying on the creative power (God) that creates it. Subjectivity is Truth: Perhaps Kierkegaard's most famous thesis is presented in his work titled Scientific Non-Conclusion Notes to Philosophical Fragments published in 1846: "Subjectivity is truth." This does not mean that truth is arbitrary or relative. For Kierkegaard, the issue is not what one believes, but how one believes. The way one embraces a truth with passionate inwardness, binding one's entire life to it, and being willing to suffer for it makes that truth existentially correct. In contrast, someone who repeats the same truth as cold, distant, and objective knowledge has no real relationship with that truth. According to Kierkegaard, a pagan who prays passionately is more in the truth than a Christian who mechanically repeats his prayer. Kierkegaard, at the age of 42, bid farewell to life while collapsing on the streets of Copenhagen, and his works were largely confined to a small Danish-speaking world. His ideas were almost completely forgotten until the early 20th century. However, this lonely and melancholic Dane left behind a treasure of thought that deeply understood the spirit of modern man, and this treasure was waiting to be discovered after the devastation of two world wars. Chapter 2: The Bridges In Between – The Development of Existential Thought at the End of the 19th Century and the Beginning of the 20th Century The path from Kierkegaard to Sartre is not a straight line. In this process, there have been other great thinkers and artists who contributed to the development of existential sensitivity. The most important of these are Friedrich Nietzsche and Fyodor Dostoevsky. Additionally, the phenomenology movement that emerged in the early 20th century would provide existentialism with a philosophical method. 2.1. Friedrich Nietzsche (1844-1900): The Death of God and the Overman: Although Nietzsche did not call himself an existentialist (such a term did not yet exist), he is one of the most important precursors of existentialism, and according to many, the strongest voice. Like Kierkegaard, he waged a total war against the abstract rationalism of Western philosophy, particularly the idea that since Plato, the "real world" is a "world of appearances" and that truth can only be found in a transcendent realm accessible through reason. According to Nietzsche, this belief in the "other world" is a sign of decadence that devalues life and existence. Nietzsche's greatest contributions to existential thought are as follows: "God is Dead": Shen Bilim (1882) in his work, the madman who cries out, "God is dead! God remains dead! And we have killed him!" strikingly expresses the condition of modern man. This is not a cry of joy, but a moment of horror and diagnosis. All moral and metaphysical certainties that uphold Western civilization (the Christian God, absolute good, objective truth) have collapsed. Humanity has found itself in a void, on the edge of an abyss. This situation is called "nihilism." Nihilism is the devaluation of the highest values. Will to Power (Der Wille zur Macht): According to Nietzsche, the fundamental drive of all life is not self-preservation or pleasure, but "will to power." This is not just the desire to dominate others, but a deeper and more creative concept: the continuous and dynamic effort to surpass oneself, to be more, to create one's own values. Man should not suppress this will to power, but should use it creatively. Overman (Übermensch) and the Revaluation of Values: Thus Spoke Zarathustra (1883-1885) proposes a new type of human to fill the void created by the death of God: the Overman. The Overman, by rejecting the slave values of herd morality (obedience, humility, compassion), is a free spirit who creates his own values, loves his own fate (amor fati), and affirms life as an infinite cycle (eternal recurrence). The Overman is awar