propositional logic
Post on 30-Dec-2015
54 Views
Preview:
DESCRIPTION
TRANSCRIPT
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 qq__~p
Not to be confused with…p v q
~p__q
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 qr qp r
Not to be confused with…p q
q rp r
Arguments Forms and Fallacies
Modus Ponens (Method of Affirming)
The fallacy in red is called Affirming the Consequent.
p qq___
p
Not to be confused with…p q
p___ q
Arguments Forms and Fallacies
Modus Tollens (Method of Destroying)
The fallacy in red is called Denying the Antecedent.
p q~p__
~q
Not to be confused with…p q
~q___ ~p
Arguments Forms and Fallacies
Constructive Dilemma
Destructive Dilemma
(p q) • (r s) p v r________ q v s
(p q) • (r s) ~q v ~s______ ~p v ~r
p qp___ q
p q~q___ ~p
See Modus Ponens in CD?
See Modus Tollens in DD?
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 Fallacies
To refute constructive and destructive dilemmas (you refute both the same way), you either Grasp by the horns Escape between the horns
Grasping by the HornsProve the conjunctive premise false by proving either conjunct false
(H S) • (O N) T F F
Escaping between the HornsProve the disjunctive premise false
For example,
For example,
H v O F F F
Show Hillary is a strong defender of free markets, say
Show, say, Edwards is going to win
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 Fallacies
To refute constructive and destructive dilemmas (you refute both the same way), you either Grasp by the horns Escape between the horns
Grasping by the HornsProve the conjunctive premise false by proving either conjunct false
(G P) • (H N) F T F
Escaping between the HornsProve the disjunctive premise false
For example,
For example,
~P v ~N F F F
Show Huckabee has reasonable religious views
Show America minds neither philanderers nor religious nuts
top related