Propositional logic
This presentation is the property of its rightful owner.
Sponsored Links
1 / 10

Propositional Logic PowerPoint PPT Presentation


  • 88 Views
  • Uploaded on
  • Presentation posted in: General

Propositional Logic. 6.6 Argument Forms and Fallacies. Arguments Forms and Fallacies. Disjunctive Syllogism p v q / q // ~p … test it with a truth table. p v q ~p __ q. Not to be confused with…. p v q q __ ~p. Arguments Forms and Fallacies. Pure Hypothetical Syllogism

Download Presentation

Propositional Logic

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Propositional logic

Propositional Logic

6.6 Argument Forms and Fallacies


Arguments forms and fallacies

Arguments Forms and Fallacies

Disjunctive Syllogism

p v q / q // ~p … test it with a truth table

p v q

~p__

q

Not to be confused with…

p v q

q__

~p


Arguments forms and fallacies1

Arguments Forms and Fallacies

Pure Hypothetical Syllogism

Pure Hypothetical Syllogism requires a chain be made where the argument in red fails to make one.

p  q

q  r

p  r

Not to be confused with…

p  q

r  q

p  r


Arguments forms and fallacies2

Arguments Forms and Fallacies

Modus Ponens (Method of Affirming)

The fallacy in red is called Affirming the Consequent.

p  q

p___

q

Not to be confused with…

p  q

q___

p


Arguments forms and fallacies3

Arguments Forms and Fallacies

Modus Tollens (Method of Destroying)

The fallacy in red is called Denying the Antecedent.

p  q

~q___

~p

Not to be confused with…

p  q

~p__

~q


Arguments forms and fallacies4

Arguments Forms and Fallacies

Constructive Dilemma

Destructive Dilemma

(p  q) • (r  s)

p v r________

q v s

p  q

p___

q

See Modus Ponens in CD?

p  q

~q___

~p

(p  q) • (r  s)

~q v ~s______

~p v ~r

See Modus Tollens in DD?


Arguments forms and fallacies5

Arguments Forms and Fallacies

If we get Hillary, then we get socialism.

If we get Obama, then we get naïveté.

We’re going to get either Hillary or Obama as the next president. So, we’ll either have socialism or naïveté .

Symbolizing…

(H  S) • (O  N)

H v O_________

S v N


Arguments forms and fallacies6

Arguments Forms and Fallacies

To refute constructive and destructive dilemmas (you refute both the same way), you either

  • Grasp by the horns

  • Escape between the horns

For example,

Grasping by the Horns

Prove the conjunctive premise false by proving either conjunct false

(H  S) • (O  N)

T  F F

Show Hillary is a strong defender of free markets, say

For example,

Show, say, Edwards is going to win

Escaping between the Horns

Prove the disjunctive premise false

H v O

F F F


Refuting constructive and destructive dilemmas

Refuting Constructive and Destructive Dilemmas

If we get Giuliani, then we get a philanderer.

If we get Huckabee, then we get a religious nut.

Either the US doesn’t want a philanderer or it doesn’t want a religious nut. So, we won’t get Giuliani or we won’t get Huckabee as president.

Symbolizing…

(G  P) • (H  N)

~P v ~N__________

~G v ~H


Arguments forms and fallacies7

Arguments Forms and Fallacies

To refute constructive and destructive dilemmas (you refute both the same way), you either

  • Grasp by the horns

  • Escape between the horns

For example,

Grasping by the Horns

Prove the conjunctive premise false by proving either conjunct false

(G  P) • (H  N)

F T  F

Show Huckabee has reasonable religious views

For example,

Show America minds neither philanderers nor religious nuts

Escaping between the Horns

Prove the disjunctive premise false

~P v ~N

F F F


  • Login