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Argument Analysis and Diagramming I


Few persons care to study logic, because everybody conceives himself to be proficient enough in the art of reasoning already.

                                                                              —Charles Sanders Peirce (1839-1914)


  • Bracket all propositions
  • Number bracketed propositions according to their order of occurrence in the argument
  • Circle premise and conclusion indicators (but not other connective or transitional terms)
  • Diagram the logical structure of the argument


1[Science predicts,] and it is because it predicts that 2[it is useful as a rule of action.]

—Henri Poincaré, The Value of Science




1. Deductive Arguments

  • Argument based on mathematics
  • Argument from definition
  • Categorical syllogism
  • Hypothetical syllogism
  • Disjunctive syllogism

2. Inductive Arguments

  • Prediction
  • Argument from analogy
  • Inductive (empirical) generalization: universal (UG) and statistical (SG)
  • Argument from authority
  • Argument based on signs
  • Causal inference
  • Statistical syllogism
  • Simple enumeration


1. Illogical atheist: If God does not exist, then there cannot be a sound argument for God’s existence. And, as a matter of fact, there is no sound argument for God’s existence. Accordingly, God does not exist.

2. Bobby Knight, controversial college basketball coach and occasional hunter: If you want to see deer in the woods, you have to be quiet. Deer tend to run away when they hear noise.

3. Child mathematician: No month can possibly have more than 23 weekdays, since the longest months contain only 31 days, and in any 31-day period there must be at least four Saturdays and four Sundays.

4. Wishful friend of a gambler: Betty Ann has consistently lost at blackjack every day for a month. Consequently, it is highly probable that she’ll win today.

5. Madame Claire Voyant: Since Aimée is a Pisces, it follows that she was born in March.

6. Fifty-something environmental activist: Jane Fonda says that nuclear power plants are dangerous. Therefore, I am compelled to conclude that nuclear power plants are actually dangerous.

7. Disillusioned and disgruntled critic of contemporary American pop culture: Either Eminem is a brilliant poet of the people or a misguided misogynist. However, he is by no means a brilliant poet of the people. Therefore, Eminem is a misguided misogynist.

8. Charlton Heston, former Hollywood actor and NRA activist: All real Americans are NRA members, so Arnold Schwarzenegger is an NRA member, since he is a real American.

9. Marriage is in the same condition as the Church: Both are becoming functionally useless. For just as God has been pronounced dead quite often but has this sneaky way of resurrecting himself, so everyone debunks marriage, yet ultimately ends up married!

—adapted from Shulamith Firestone, The Dialectic of Sex: The Case for Feminist Revolution.

10. Anxious child: Mom, dad, we’re almost there! I just saw a sign that said New York City next exit.

11. Donald Rumsfeld, U. S. Secretary of Defense: If we don’t preemptively strike Iraq then Saddam will possess weapons of mass destruction (WMB). And if Saddam possesses weapons of mass destruction then he will use them against the United States. Therefore, if we don’t preemptively strike Iraq then Saddam will use weapons of mass destruction against the United States.

12. Interstate truck driver: Man, I’ve been listening for a whole month to Dick Gordon on the NPR radio program The Connection. And he hasn’t discussed the enormous cultural influence of country music and NASCAR even once! Needless to say, The Connection will never, discuss the enormous cultural influence of country music and NASCAR.

13. Journalism major at Brown University:  95 % of American militia members get their news from the National Inquirer or Entertainment Tonight. My roommate, Jethro Wyteguy, is an avid and active member of the Montana militia. Accordingly, Jethro probably gets his news from the National Inquirer or Entertainment Tonight.

14. Shakespeare’s Hamlet, Prince of Denmark is longer than 300 pages since James Joyce’s Ulysses is longer than 300 pages, and Homer’s The Odyssey is longer than 300 pages, and Albert Camus’ The Stranger is longer than 300 pages, and Fyodor Dostoevsky’s Brothers Karamazov is longer than 300 pages.

15. Incredulous media researcher and critic: Recent surveys show that at least 75% of American males, ages 16-25, watch “reality TV” at least 10 hours a week. Therefore, probably 75% of all Americans watch “reality TV” at least 10 hours a week.

16. College student to roommate: I wouldn’t have that fifth tequila if I were you; your head will be splitting in the morning!

17. Charles Sullivan, CCRI English professor: The military term “collateral damage” is a euphemism for the injuring or death of innocent civilians. Therefore, the military term “collateral damage” is an inoffensive phrase that protects us from acknowledging an unpleasant, harsh or distasteful reality.