Reason as a source of knowledge

• Plato's slave boy argument for innatism

  P1: The slave boy has no prior knowledge of geometry.

  P2: Socrates only asks questions; he does not teach the boy about geometry.

  P3: After the questioning, the slave boy can grasp an eternal truth about geometry.

  P4: This eternal truth was not derived from the boy's prior experience, nor from Socrates.

  C: The boy must have known this eternal truth innately.
• Leibniz's argument for innatism based on necessary truths

  P1: The senses only reveal instances of general truths.

  P2: The senses cannot reveal the necessity of a general truth.

  P3: Our minds can see the necessity of some general truths.

  C: Our ability to see the necessity of general truth is not derived from the senses, but is based on innate principles.
• Locke's first argument against innatism

  P1: Any innate idea, x, if it exists, would be universally held.

  P2: Children and idiots do not have the ideas of x.

  P3: If any idea is held in the mind then you must be aware of it.

  C: Therefore x is not universally held and cannot be innate.
• Locke's second argument against innatism based on the transparency of ideas.

  • We are conscious of or have been conscious of at some point, everything in our minds.
  • If we had innate knowledge, we could have never been conscious of it in the past.
  • Therefore there is no innate knowledge.
• Locke's third argument against innatism

  If we need experience to access innate knowledge then there is no way to distinguish it from knowledge gained by experience.

  Therefore the concept of innate knowledge is incoherent.
• Tabula rasa

  P1: The theory innatism claims we are born with innate ideas.

  P2: The tabula rasa theory shows that all our ideas are derived from experience.

  C: Therefore the theory of innatism is redundant.
• Hume's Fork

  All knowledge is either:

  • a priori relations of ideas.
  • a posteriori matters of fact.
• Intuition

  A single act of the intellect whereby you inwardly look upon a proposition and immediately understand that it's true.
• Deduction

  A multi-stage process whereby you infer what must follow from other facts.
• Rene Descartes' notion of clear and distinct ideas:

  • An idea is clear if it is very bright and present in the mind.
  • An idea is distinct if it is sharply separated from other ideas.
  • Clear and distinct ideas are propositions you can know by intuition alone.
• The cogito as an example of an a priori intuition

  P1: I am thinking.

  P2: All thinking things exist.

  C: Therefore I exist.
• The trademark argument

  P1: The cause of anything must be at least as perfect as its effect.

  P2: My ideas must be caused by something.

  P3: I am an imperfect being.

  P4: I have the idea of God, which is that of a perfect being.

  IC1: I cannot be the cause of my idea of God.

  IC2: Only a perfect being (God) can be the cause of my idea of God.

  C: God must exist.
• Descartes' contingency argument


  P1: The cause of my existence as a thinking thing must be a) myself, b) I have always existed, c) my parents, or d) God.

  P2: I cannot have caused my self to exist for then I would have created myself perfect.

  P3: Neither have I always existed, for then I would be aware of this.

  P4: My parents may be the cause of my physical existence but they cannot explain me as a thinking mind.

  C: Therefore only God could have created me.
• Descartes' ontological argument 


  P1: I have an idea of God, a perfect being.

  P2: A perfect being must have all perfections.

  P3: Existence is a perfection.

  C: Therefore God exists.
• Descartes' proof of the external world (an a priori deduction) step 1a

  P1: The will is a part of my essence.

  P2: Sensation is not subject to my will.

  C: Sensations come from outside of me.
• Descartes' proof of the external world step 1b


  P1: My nature or essence is unextended.

  P2: Sensations are ideas of extended things.

  C: Sensations come from outside of me.
• Descartes' proof of the external world step 2

  P1: There are two possible sources for the origin of sensation: God or matter.

  P2: I have a strong natural inclination to believe that they come from matter, and no faculty by which to correct this belief.

  IC: So if there origin were in God, then God would be a deceiver.

  P3: God is not a deceiver.

  C: Sensation originates in matter.