Aristotle was an Ancient Greek philosopher alive between 384 and 322 BCE. Born in Stagira in northern Greece, he studied at Plato’s Academy in Athens before founding his school, the Lyceum. Aristotle’s writings span an extraordinary range, including metaphysics, logic, science, politics, and ethics. His systematic approach to knowledge laid the foundation for Western philosophy and science, especially through the development of formal logic and his emphasis on observation, definition, and classification.

For Arendt, Aristotle’s work is crucial. Aristotle provides Arendt with distinctions and definitions that are essential to her work. His separation of human activities undergirds her account of both the vita activa and vita contemplativa. Aristotle elevates contemplation as the highest human activity but does not define will. He argues in Nicomachean Ethics that the goal of life is to live well by mediating between desire and reason. Arendt admires Aristotle’s attention to worldly plurality and his distinction of human activities, but she emphasizes that Aristotle, like Plato, shaped Western tradition away from the world of appearances. In her reading, Aristotle exemplifies both the richness and limits of the classical tradition: He provided indispensable categories for thought, but he also helped establish a hierarchy that distanced philosophy from political life.

In her work, Arendt traces Aristotle to Augustine of Hippo who was alive from 354 to 430 CE. Augustine is considered a foundation figure in late antiquity and Christian philosophy. He was born a Roman in North Africa and received a classical education before converting to Christianity. After he was ordained Hippo Regius, he wrote extensively in the areas of theology, philosophy, and the nature of human existence. His religious beliefs deeply impacted his work. Confessions and The City of God continue to shape Western thought on sin, grace, and memory.

Augustine is arguably Arendt’s deepest lifelong source material. In her work, he provided the foundation for the concepts of will and freedom. Augustine recognized an inner faculty that could affirm or resist reason, giving humans the power to either obey or rebel. Arendt also draws heavily from Augustine’s assertion that humans are beings who can create anew, an idea she uses to shape her own definition of will. In her section on willing, Arendt highlights Augustine as the first to grasp the Will as an inner faculty, introducing a new depth to the self.

René Descartes is often referred to as the “father of modern philosophy.” Born in France in 1596, Descartes trained in mathematics, philosophy, and science. In works such as Meditations on First Philosophy and Discourse on Method, Descartes developed a system that attempted to provide absolute certainty by beginning with doubt and then proceeding through clear, rational steps.

For Arendt, Descartes embodies the decisive modern turn inward and the championing of rationalism. His philosophy shifted the focus of thought from the shared world of appearance to the solitary certainty of the thinking subject. In The Life of the Mind, Arendt notes that this move profoundly shaped the conditions of philosophy: Rather than being grounded in plurality and dialogue, as it was with Socrates, thought became an activity sealed within the individual.

Arendt suggests that Descartes’s famous line, “I think, therefore I am,” is problematic. It reorients philosophy with the idea of subjective consciousness, but it comes at a price. The certainty of thought becomes self-enclosed, undermining the role of shared judgment and political responsibility. In a world where truth is reduced to what can be verified internally, individuals risk retreating from dialogue and action into private certainty. Arendt argues that Descartes presented an idea that championed the primacy of the self and, in doing so, severed the individual from the plurality of worldly experience.

Epictetus was a Greek Stoic philosopher whose life from 50-135 CE and teaching epitomized the Stoic emphasis on inner freedom. Born into enslavement in the Roman Empire, he eventually gained his freedom and studied philosophy. He later established his own school. Epictetus stressed that while human beings cannot control external events, they can control their judgments, desires, and choices. For him, freedom did not depend on power or wealth but on the mastery of the self.

Epictetus marks an important shift in Arendt’s genealogical study of the Will. In The Life of the Mind, she notes that Stoicism arose during a period of political turmoil under the Roman Empire. With the decline in participatory freedom, philosophy turned inward. The Stoics, especially Epictetus, advance the idea that freedom resides in the inner will. Arendt highlights this as crucial in the genealogy of the Will: In a world of political turmoil, the Will became a private refuge. She admires the Stoic dignity but is critical of this retreat from worldly matters. For Arendt, Stoicism represents both resilience and loss—the preservation of the self at the cost of plurality.

Martin Heidegger was a German philosopher whose work on phenomenology and existential ontology impacted 20th-century thought. Heidegger studied theology and philosophy before studying under Edmund Husserl, considered to be the founder of phenomenology. Heidegger’s seminal work, Being and Time, sought to revive the question of Being itself, which he believed had been neglected since the ancient Greeks. Heidegger’s thought deeply influenced existentialism and postmodern philosophy, though his legacy is complicated by his involvement with the Nazi regime in the 1930s.

For Hannah Arendt, who studied under Heidegger and was personally entangled with him, his philosophy was both indispensable and troubling. In The Life of the Mind, she engages his analysis of Being, temporality, and authenticity, especially his claim that thought should return to the question of Being. She draws on his phenomenological method to articulate thinking as an activity distinct from willing and judging. For Arendt, Heidegger is fundamental to her work, as well as problematic. His development in phenomenology helps her articulate thinking as a distinct activity, but his retreat from the political world exemplifies the dangers of withdrawing into Being and the metaphysical.

Arendt points to Heidegger as an example of the dangers of retreating entirely into the thinking ego and the metaphysical realm. She argues that the primacy of metaphysics causes professional thinkers to become vulnerable to dangerous ideologies. Heidegger’s withdrawal into the language of Being, and his avoidance of political responsibility, embodies for her the philosopher’s temptation to abandon the public world.

Immanuel Kant was a German philosopher during the 18th century whose critical philosophy reshaped the Enlightenment and set the terms for much of modern thought. Born in East Prussia, where he lived his entire life, Kant taught at the local university and became renowned for his rigor and systematic approach. His three critiques—Critique of Pure Reason, Critique of Practical Reason, and Critique of Judgment—sought to map the limits and possibilities of human knowledge, morality, and criticism. Kant argued that while we cannot know the “thing-in-itself,” we can know appearances as they are structured by the categories of the mind.

Arendt admires Kant’s effort to ground freedom in reason and to situate morality in self-legislation rather than external authority, but she is critical of his ideologies which promote the primacy of the self. She argues that Kant, like many other professional thinkers, is biased against the world of appearances. However, Arendt sees Kant as a thinker who did not escape the world but sought to understand the conditions for experience and judgment. She takes him as a model for how reflective thought could form political responsibility. Unlike Plato, who fled the world of appearances, Kant sought to understand the conditions of human experience within it. For Arendt, this made him a thinker who, despite his limitations, could help bridge philosophy and the worldly realm of politics.