1. PHIL 151
Week 8

3. Week 1
Propositional Logic

4. Propositional Logic Statement Premises (and hidden premises)
Conclusion
Argument
Validity
Truth
Soundness
contradiction

5. Propositional Logic Soundness Truth Validity Premises True premises
Meaning (semantics)
Are the premises true?
Validity
Argument
Structure (syntax)
the truth of the premises guarantees the truth of the conclusion.
Soundness
True premises

6. Propositional Logic Argument
John is not going to class today because he is wearing shorts, and he never goes to class wearing shorts.
Standard form
John never goes to class wearing shorts.
John is wearing sorts.
-­‐-­‐
John is not going to class today.

7. Propositional Logic
Hidden premises Felix is a cat. Cats hate birds. So, Felix hates Tweety. Felix is a cat. Cats hate birds. Tweety is a bird -­‐-­‐ Felix hates Tweety Cats hate birds

8. Week 2
Propositional logic

9. Propositional Logic Simple vs. complex statements
Connectives (and, or, if, not)
Truth Conditions
Conditionals
Argument forms

10. Logical connectives p q
p and q
p or q
if p then q T F

11. Propositional Logic - Conditionals

12. Propositional Logic – propositional argument form
I’ll have steak or a burger. If I have steak, I’ll feel full. If I have a burger, I’ll feel full. -- I’ll feel full. P: I’ll have steak Q: I’ll have a burger R: I’ll feel full P or Q If P then Q If Q then R -- R VALID

13. Week 3
Propositional Logic

16. 2 ways in which a form is improper
the argument is not a substitution
It uses logical connectives

17. Truth tables – evaluating arguments
A truth table is simply a table that represents all possible combinations of truth and falsity for the sentence letters & sentences in an argument.
If P then Q
If R then Q --
If P then R
is there a row where the premises are true and the conclusion false?

18. Truth trees
Another way of determining validity is by using truth trees. For complex arguments, truth trees are simpler than truth tables.
Truth trees are based on decomposition rules for different logical connectives.

19. Truth trees

20. If P then Q
If R then Q --
If P then R

21. Week 4

22. Lecture Categorical Statements – predicative logic
 propositional logic
Objects (individuals)
Categories (predicates)
Quantifiers (all, some, no)
Universal (all)
Existential (some)
Logical equivalents (Converse, Obverse, Contraposition)
Logical equivalent/ contraditory / contrary

23. Categorical argument
All cats are ferocious No ferocious things are friendly. -- No cats are friendly. All A are B No B are C -- No A are C Valid

24. Categorical argument
All C are M Cf -- Mf

25. Logical equivalents All birds have wings Converse: (change the order)
All winged-things are birds
Obverse: (change the value)
No birds are non-winged things
Contraposition: (change the value and the order)
All non-winged things are non-birds

26. Circle diagram

27. All A are B
No B are C
-- No A are C A B C

28. All fish have gills. Nemo is a fish. So Nemo has gills.
All F have G Fn
Fn G -- Gn

29. 8. No cats are vegans. No vegans eat meat. So all cats eat meat.
No C are V No V eat M -- All C eat M C M V Invalid

30. Week 5
Meaning

31. Meaning Problems of meaning
Extentional: all the individuals (universal)
ostensive (one example, pointing out drawing)
Enumerative (lists examples of term)
Intensional: idea, or the concept of that individual
Synonomous (give other terms with the same meaning
Operational (describe a test to be used in applying a term)
Problems of meaning
Vagueness (Grey area)
Ambiguity (the term has two meanings simultaneously)
Equivocation (Same term appears each time with a different menaing)

32. Good definition?
‘Triangle’ means a three-sided figure.

33. Week 7
Fallacies

34. A Dozen Fallacies
Come up with your own examples of each of the following fallacies, and then explain the flaw in your example.
Equivocation
Red Herring
Slippery Slope
Begging the Question
Appeal to Pity
Burden of Proof/No Nay-sayers
Appeal to the People
Ad Hominem Abusive, Circumstantial, and Tu Quoque
Post-hoc ergo propter hoc
No True Scotsman
Texas Sharp-Shooter
Straw Person

35. Evaluate the following argument for fallacies
People should be able to play whatever games they like online. Playing an online game usually just means walking around and talking to other people, and in a free and democratic society, freedom of speech is a fundamental right. Some online games may seem violent, but since they’re just ‘games’, they aren’t truly violent: by definition, games are fun. If we don’t want to be victims of a moralistic crusade, we should stand up for freedom online.
Red herring: “in a free and democratic society, freedom of speech...” Begging the question: “since they’re just ‘games’ they aren’t truly violent” Red herring: “by definition, games are fun”. (Could also be begging the question). Straw person: “If we don’t want to be victims...”