Department of Philosophy (PHI)

  1. Philosophy at UNCG
    1. Philosophy Department Home
    2. Faculty and Staff
    3. Why Study Philosophy?
    4. Degree Program
    5. Courses
      1. Courses for Spring 09
    6. Roger Schwirk Award for Excellence in Philosophy
    7. Philosophy Club Great Conversation Series
    8. Biennial Symposium in Philosophy
  2. Philosophy on the Web
    1. Stanford Encyclopedia of Philosophy
    2. Internet Encyclopedia of Philosophy
    3. Guide to Philosophy on the Internet
  3. Pre-Professional Program in Law
    1. Pre-Professional Program in Law Brochure [pdf]
    2. Pre-law Information and Suggestions for Freshmen, Sophomores, and Transfer Students
    3. Pre-law Information and Suggestions for Juniors and Seniors
  4. Prof. King's Course Materials
    1. Arguments
    2. Conditional Statements vs. Arguments
    3. Conclusion Identification Quizzes
    4. Argument Structure
    5. Argument Structure Quizzes
    6. Deduction, Induction and Fallacy
    7. Validity
    8. Conditionals and Simple Conditional Arguments
    9. Hypothetical Syllogism and related fallacies
    10. Disjunctions
    11. Dilemmas
    12. Statements Equivalent to Conditionals
    13. Conditionals and Variations (Table)
    14. Categorical Statements
    15. Interpretation Quizzes
    16. Venn Diagrams for Categorical Statements
    17. Validity Testing by Venn Diagrams
    18. Equivalences Among Categorical Statements
    19. Four Varieties of Induction

Disjunctions ('OR'-type compounds)

A disjunction is true when one or both of its disjuncts (components) are true, and false when both of its disjuncts are false, as indicated in the table:

Al is here Bill is here Al is here or Bill is here
True True True
True False True
False True True
False False False

If a true disjunction has a false disjunct, we can deduce that the other disjunct is true, so the following are valid arguments (disjunctive syllogisms):

Al or Bill is here Al or Bill is here
Al is not here Bill is not here
Therefore Bill is here (valid) Therefore Al is here (valid)

But if a true disjunction has a true disjunct, we cannot deduce that the other disjunct is false, so the following arguments are invalid (disjunctive fallacy):

Al or Bill is here Al or Bill is here
Al is here Bill is here
So Bill is not here (invalid) So Al is not here (invalid)
 
 

Page updated: 04-Dec-2006

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Department of Philosophy
The University of North Carolina at Greensboro
216 Foust Building,
Greensboro, NC 27402-6170
VOICE 336.334-5059
FAX 336.334-4720
EMAIL d_lefkow@uncg.edu