Socrates is widely regarded as the father of Western philosophy due to his profound influence on the development of philosophical thought in ancient Greece.

Plato's theory of Forms, also known as the theory of Ideas, is a central concept in his philosophy, positing that there is a realm of perfect and unchanging Forms or Ideas that exist independently of the physical world.

Aristotle made significant contributions to logic, developing the syllogism and other logical principles, and he is also credited with developing the scientific method, emphasizing observation and empirical evidence.

René Descartes is famous for his philosophical statement 'Cogito, ergo sum' ('I think, therefore I am'), which serves as the foundation of his epistemological and metaphysical inquiries.

Jean-Jacques Rousseau is renowned for his social contract theory, which emphasizes the importance of the 'general will' and the sovereignty of the people in a just society.

Immanuel Kant is known for his moral philosophy, particularly the concept of the 'categorical imperative,' which emphasizes the importance of acting according to universal moral principles.

Jean-Paul Sartre is widely regarded as one of the most influential philosophers of the 20th century, known for his existentialist philosophy, which explores themes of freedom, responsibility, and the meaning of existence.

Friedrich Nietzsche is known for his philosophy of 'will to power' and the concept of 'Übermensch' ('superman'), which emphasize the importance of individual self-assertion and the rejection of conventional morality.

Bertrand Russell is widely regarded as the father of modern analytic philosophy, known for his contributions to logic, philosophy of language, and his work on the foundations of mathematics.

Søren Kierkegaard is known for his existentialist philosophy, particularly his exploration of 'existential angst' and the concept of 'authenticity,' emphasizing the importance of individual choice and commitment in the face of uncertainty.

John Rawls is widely regarded as one of the most influential philosophers of the 20th century, known for his work on ethics and political philosophy, particularly his theory of justice and the concept of the 'veil of ignorance.'

Ludwig Wittgenstein is known for his philosophy of 'ordinary language,' emphasizing the importance of understanding the meaning of words and concepts in their everyday context, and his concept of the 'linguistic turn,' which shifted the focus of philosophy towards the analysis of language.

David Lewis is widely regarded as one of the most influential philosophers of the 20th century, known for his work on metaphysics, particularly his theory of possible worlds and his contributions to the philosophy of mind.

Jacques Derrida is known for his philosophy of 'deconstruction,' which involves critically examining the assumptions and structures of language and thought, and his concept of 'difference,' emphasizing the importance of recognizing and embracing diversity and otherness.

Jürgen Habermas is widely regarded as one of the most influential philosophers of the 20th century, known for his work on ethics, political philosophy, and his theory of communicative action, which emphasizes the importance of dialogue and consensus-building in democratic societies.