The limits of knowledge

• Philosophical scepticism


  Casts theoretical doubt over almost everything we know
• Philosophical scepticism vs normal incredulity

  1. Philosophical scepticism is extreme.
  2. Normal incredulity is sensitive to evidence, while philosophical scepticism remains theoretical.
  3. Normal incredulity remains local, while theoretical scepticism can be global.
• The role of philosophical scepticism

  In epistemology, philosophical scepticism is used to test the strength of our knowledge claims.
• Descartes' first wave of doubt

  • Descartes' senses have sometimes deceived him so it would be wise not to trust them.
  • This casts doubt over the whole of our sense experiences.
• Descartes' second wave of doubt

  • Descartes has dreams which are just like being awake so he cannot be sure that he is not dreaming now.
  • This means everything I perceive around me could be false.
• Descartes' third wave of doubt

  • Descartes imagines a powerful and malicious demon using all its energies to deceive him about the existence of the physical world
• Descartes' response to scepticism

  • Uses intuition and deduction to reach a belief in the cogito which even the demon hypothesis cannot make him doubt.
  • He uses this clear and distinct idea to deduce further truths and free himself from doubt.
  • E.g. proof of the external world, trademark argument.
• Locke's empiricist response to scepticism

  • An indirect realist who believed our knowledge is confined to the world as we perceive it through our senses.
  • However scepticism about the existence of the external world is not possible at a practical level.
  • It does not affect our lives and the practical business of living should be what matters to us.
• Berkeley's empiricist response to scepticism

  • An idealist who believed there is no gap between perception and the objects.
  • By denying that matter exists, Berkeley asserts that we have secure knowledge of reality because it is within our minds.
  • This leaves no room for sceptical arguments.
• Russell's empiricist response to scepticism

  • The existence of the external world cannot be demonstrated conclusively.
  • However the existence of an external world is by far the best hypothesis.
  • There is no positive evidence to believe the alternatives.
  • Furthermore it can explain the regularity and predictability of our sense experiences.
• Reliabilism's response to scepticism

  • As knowledge is a reliably formed true belief, we can have knowledge without justification.
  • This means sceptical arguments cannot exploit weaknesses in justification.