The reason for writing this article is of a personal nature. I plan to do a number of things in the coming weeks or months that I have intended to do for a long time, and one of those things is to delve deeper into the field of philosophy. In this article, I list the 10 most important works of philosophy, and I will read them all in the near future and then post separate reviews of them on this Substack as soon as possible. I recommend that every reader do the same.

I: Brief introduction and clarification of the article

In accordance with the title, this article is about the foundation works of 21st-century philosophy. Of course, it is not about works written in the 21st century, but about the philosophical books that are still most relevant in the 21st century. And there are many of them. For it is not, as is sometimes thought, that the ideas and thoughts prevalent in the world at a given moment have a major influence on the philosophical theories conceived and developed during that time. It is the other way around. The personal philosophies of a small number of the greatest thinkers in history have played an immeasurably large role in shaping the way people still think and act today.

II: List of books

I refuse to waste any more time, and we proceed to the order of the day. As far as I am concerned, the list of the most influential books of philosophy of all time—and thus still relevant in 2026 and undoubtedly in the decades that follow—is as follows. No philosopher who takes himself or other philosophers even remotely seriously can disagree with this:

1. The Republic (c. 375 BC)
2. Metaphysics (4th century BC)
3. Confessions (c. 400)
4. Summa Theologica (1265–1274)
5. Meditations on First Philosophy (1641)
6. Critique of Pure Reason (1781/1787)
7. Phenomenology of Spirit (1807)
8. Capital (1867)
9. Thus Spoke Zarathustra (1883–1885)
10. Being and Time (1927)

That does, of course, not mean that all these philosophies are useful, logical, or even remotely logical, or that they are in perfect agreement with one another. However, it is not without reason that they have become so influential. So it is impossible and absolutely ridiculous to have an opinion about these books, or about philosophy in general, or about numerous world events in the past, present, and future, if you have never read these books.

1: Plato – The Republic

Perhaps the most influential philosophical book ever written. Plato addresses justice, knowledge, education, politics, and the famous allegory of the cave. Virtually all of Western philosophy has remained inspired by Plato. It had an immeasurable influence on political philosophy, ethics, epistemology, and metaphysics.

2: Aristotle – Metaphysics

Aristotle develops a systematic philosophy regarding being, cause, substance, and logic. His thought determined science and philosophy for nearly two thousand years. Influence on logic, natural philosophy, science, and theology.

3: Augustine – Confessions

Not only an autobiography, but also a profound philosophical inquiry into time, memory, will, and self-knowledge. The book connects classical philosophy with Christianity. Influence on psychology, philosophy of religion, and existentialism.

4: Thomas Aquinas – Summa Theologica

A monumental synthesis of Aristotle and Christianity. For centuries, the definitive standard work of Catholic philosophy. Influence: scholasticism, ethics, natural law, political theory.

5: Descartes – Meditations on First Philosophy

With his methodical doubt, Descartes effectively begins modern philosophy. The famous premise: “I think, therefore I am.” Although that formulation comes from another work (Treatise on Method), the idea is fully developed in the Meditations. Influence: rationalism, epistemology, modern science.

6: Kant – Critique of Pure Reason

Many historians call this the most important philosophical work since Aristotle. Kant investigates what we can know, how experience is possible, why science works, and where the limits of reason lie. Virtually every later philosopher responds to Kant. Anyone who does not is not a philosopher.

7: Hegel – Phenomenology of Spirit

Hegel describes the development of consciousness, history, and freedom as a dynamic process. His influence extends to Marx, Kierkegaard, existentialism, phenomenology, political theory, and modern philosophy of history. All later political ideologies and philosophical thinkers have been influenced by Hegel.

8: Marx – Capital

Although it is also an economic and political work, it is simultaneously a profound philosophical work on labor, alienation, history, and power. Its political influence can hardly be overestimated. It influenced socialism, communism, sociology, critical theory, and economic philosophy in general.

This book was the foundation of communism, and communism, regardless of whether one is positive or negative towards it, was the dominant factor in the entire global political life of the 20th century, and perhaps still is. Not to mention the fact that the other major political theories of the 20th century—fascism and the modern variants of liberalism and social democracy—were largely a reaction to communism. It is impossible to know or even imagine how differently history would have unfolded without Marx’s Capital, whether positively or negatively.

9: Nietzsche – Thus Spoke Zarathustra

Nietzsche’s most literary book introduces ideas such as the Übermensch, the alleged “death of God,” self-creation, the will to power, and eternal recurrence. His influence is enormous on existentialism, psychology, literature, and postmodernism. The tragic figure of Friedrich Nietzsche still has a major influence on Western thought.

10: Heidegger – Being and Time

Perhaps the most important philosophical book of the twentieth century. Heidegger poses the question anew: What does it actually mean to be? He influenced Sartre, Gadamer, Arendt, Derrida, Levinas, and Merleau-Ponty, among others.

III: A small side note

A purely Western top 10 of philosophy like this actually does not do justice to world history. Then the following works would certainly deserve a place as well:

1. Daodejing (Taoism)
2. Analects (Confucianism)
3. Bhagavad Gita
4. Mūlamadhyamakakārikā (Buddhist philosophy)

These works have each influenced hundreds of millions of people and entire civilizations, on a scale comparable to Plato, Aristotle, and Kant in the Western tradition. However, they have had less influence on philosophy and on the course of events in other parts of the world. Nevertheless, I am aware of their importance and depth. So please forgive me for their absence from this list. I will undoubtedly return to this after the summer.

IV: Conclusion

In the coming period, the reader can expect 10 extensive and accessible reviews of the above-mentioned books on the same Substack. I hope to welcome you all back to this website soon, and I wish everyone a sporty, intellectual, productive, meaningful, and above all happy, sunny, and carefree summer holiday!