Lecture on Soundness in Philosophy

Introduction

• Presenter: Aaron Ansell, Graduate Student at Duke University.
• Purpose: Discuss the notion of soundness in evaluating arguments in philosophy.
• Background Knowledge: Understanding of validity is required.

Validity Recap

• Definition: An argument is valid if it is impossible for the premises to be true while the conclusion is false.
• Example of Valid Argument:
  • Premise 1: All cats are purple.
  • Premise 2: Everything that is purple is a person.
  • Conclusion: Therefore, all cats are people.
• Observation: A valid argument may not have true premises or a true conclusion.

Soundness in Philosophy

• Definition: Applies only to deductive arguments.
• Requirements for Soundness:
  1. The argument must be valid.
  2. All premises of the argument must be true.
• Implication: An unsound argument can have either false premises or be invalid.

Examples of Soundness

1. Invalid but True Premises:

   • Premise 1: All dead parrots are dead.
   • Premise 2: Parrots are not frogs.
   • Conclusion: Therefore, frogs exist.
   • Analysis: True premises but invalid argument (conclusion doesn't follow).

2. Invalid and False Premises:

   • Premise 1: Ostriches cannot fly.
   • Premise 2: All insects wear top hats.
   • Conclusion: Therefore, ostriches are insects.
   • Analysis: Invalid argument and false premise.

3. Valid and True Premises (Sound Argument):

   • Premise 1: Whales do not have fur.
   • Premise 2: Whales are mammals.
   • Conclusion: Therefore, not all mammals have fur.
   • Analysis: Argument is valid and premises are true, hence sound.

Importance of Soundness

• Certainty: A sound argument guarantees the truth of the conclusion.
• Utility: Sound arguments establish truths.

Conclusion

• Understanding soundness helps in evaluating the truthfulness of arguments in philosophy.
• Encouragement to practice: Try creating a sound argument.