4.1 Scepticism of the External World

Q: What is external world skepticism?

A: External world skepticism is the philosophical view that we cannot have certain knowledge about the external world and that our perceptions may not accurately reflect reality.

Q: What is the difference between vertical and horizontal skepticism in inferring from perceptions?

A: Vertical skepticism questions the reliability of our perception abilities to accurately perceive reality, while horizontal skepticism questions the existence of an external world independent of our minds.

Q: What are some variants of external world skepticism discussed?

A: Some variants include skepticism related to dreaming, the concept of an evil demon deceiving our senses, and the brain in a vat theory where our perceptions are manipulated by a supercomputer.

Q: How did Descartes express his certainty starting with 'Cogito Ergo Sum'?

A: Descartes expressed his certainty by starting with the proposition 'Cogito Ergo Sum,' which means 'I think, therefore I am,' indicating that the act of doubting or thinking itself proves one's existence.

Q: What method did Descartes use to derive knowledge from his own existence?

A: Descartes used the method of radical doubt, systematically doubting everything that could be doubted to arrive at a foundation of knowledge based on indubitable truths.

Q: What is Descartes' circular argument?

A: Descartes' circular argument refers to the criticism that he used clear and distinct perceptions to prove the existence of God, while also relying on God to ensure the reliability of clear and distinct perceptions.

Q: Why is there an issue with relying on clear and distinct perceptions to prove God and existence?

A: The issue arises because Descartes' argument seems to create a circular dependence where the existence of God is used to guarantee the reliability of clear and distinct perceptions, which are then used to prove the existence of God.