Lecture on Truth and Validity

Presenter

• Julianne Chung
• Graduate student at Yale University

Key Topics

• Truth and validity in arguments

Important Qualities of Arguments

• Clarity, Interest, Persuasiveness
• Focus of lecture: Truth and Validity

Truth in Philosophy

• Truth and falsity are properties of statements, not arguments
• Premises can be true if they agree with the facts

Validity in Philosophy

• Validity is a property of arguments
• An argument is valid if the conclusion logically follows from the premises
• Truth of premises guarantees the truth of the conclusion

Examples of Arguments

True Premises and Valid Argument

• Premise 1: All Australian Shepherds are dogs
• Premise 2: Split is an Australian Shepherd
• Conclusion: Therefore, Split is a dog

True Premises and Invalid Argument

• Premise 1: All dogs are animals
• Premise 2: All cats are animals
• Conclusion: Therefore, all cats are dogs
• Conclusion does not logically follow

True Premises, True Conclusion, but Invalid

• Premise 1: All dogs are animals
• Premise 2: All Australian Shepherds are animals
• Conclusion: Therefore, all Australian Shepherds are dogs

False Premise and Valid Argument

• Premise 1: You can't teach an old dog new tricks
• Premise 2: Split is an old dog
• Conclusion: Therefore, you can't teach Split new tricks
• Reasoning is valid, but first premise is false

False Premise and Invalid Argument

• Premise 1: I like Split
• Premise 2: Training dogs is easy
• Conclusion: Therefore, I'll win a lot of awards for teaching Split how to roll over
• Premise 2 is false, conclusion does not follow

Combinations of Truth and Validity

• Possibility 1: True premises, valid reasoning (Sound argument)
• Possibility 2: True premises, invalid reasoning
• Possibility 3: False premises, valid reasoning
• Possibility 4: False premises, invalid reasoning

Importance of Valid but Possibly False Premises

• Often unsure of the truth of premises
• Valid inference helps assess premise truth
• False conclusion from valid argument indicates false premise

Example of Valid Argument with Questionable Premises

• Premise 1: John is in bed with the flu
• Premise 2: If John has the flu, he is not bowling
• Conclusion: John is not bowling
• If John is seen bowling, Premise 1 is false

Conclusion

• Understanding argument validity is crucial even if premise truth is uncertain

Further Resources

• Paul's video on Validity
• Aaron's video on Soundness