Logic 9
Home > Flashcards > Print Preview
The flashcards below were created by user
faulkebr
on
FreezingBlue Flashcards. What would you like to do?

2 kinds of symbolic logic:
 1. Simple (atomic)
 2. Compound (complex)

Simple (atomic)
 has no other part to it.
 Ex: Columbia is the capital of S.C.

Compound (complex)
 Statement that contains another statement as a component
 Ex: The lights are on, the lights are off
 In order to have a complex statement, you must be able to replace it with something that makes sense.

Common compound propositions:
Their parts are called:

Conjuncts are connected together with the word:
 And
 Yet
 But
 Never the less
 Ex: Andrew went swimming and Susan went hiking


Propositional variables=
p, q, r, s.....

Truth Functional Component
Any component of a compound statement whose replacement by another statement having the same truth value would notchange the truth value of the compound statement

Exclusive Sense of Disjunction:
It is either one or the other, BUT not both are true

Inclusive sense of disjunction
 One or the other or both may be true
 Ex: Getting a 3.8 gpa will get you on the deans list, or having a 3.9 will...

Disjunctions "v" will only be false when:
both p and q are false

Conditional statements:
a compound statement with the form, "if p, then q"

Antecedent in a conditional statement:
the component that immediately follows the "if"

Consequent in a conditional statement:
component that immediately follows the "then"

Implication:
the relation that holds between the antecedent and the consequent of a conditional state.

Whenever you have a true antecedent:
the whole thing will be true

If Combes was a rockstar he'd be famous
Combes isnt a rockstar
Therefore Combes isnt famous
C (horseshoe) F
 C
 F
This is nota good argument...
refutation by counter example:
 If obama were a rockstar hed be famous
 Obama isnt a rockstar
 Therefore obama is famous

Valid argument=
When youhave true premises and true conclusions

True premises and False conclusion=
invalidity

Material implication:
 Symbolized by the horseshoe
 p materially implies q
 is true when either p is false, or q is trueq

Refutation by logical analogy:
exhibiting the fault of an argument by presenting another argument with the same form whose premises are known to be true and whose conclusion is known to be false
The obama and combes example of being a rockstar

Statement variable:
A letter (lower case) for which a statement may be substituted

Invalid argument form:
argument form that has at least one substitution instance with true premises and a false conclusion

Valid argument form
argument form that has no substitution instances with true premises and a false con.

Disjunctive Syllogism:
a valid argument where one premise is a disjunction, another premise is is the denial of one of the two disjuncts, and the conclusion is the truth of the other disjunct.

Modus Ponens:
A valid argument that relies on a conditional premise, and another premise affirms the antecedent of that conditional, and the conclusion affirms its consequent

Modus Tollens:
Valid argument that relies on a conditional premise and another premise denies the consequent of that conditional, and the conclusion denies its antecedent

Hypothetical Syllogism:
Valid argument containing only conditional propositions.
 p (horseshoe) q
 q (horseshoe) r
 p (horseshoe) r

Common invalid forms
 1. Fallacy of affirming the consequent
 2. Fallacy of denying the antecedent

Fallacy of affirming the consequent:
Fallacy in which the second premise of an argument affirms the consequent of a conditional premise and the conclusion of its argument affirms its antecedent.

Fallacy of denying the antecedent:
Fallacy in which the second premise of an argument denies the antecedent of a conditional premise and the conclusion of the argument denies its consequent

Tautologous Statement form:
A statement form that has only true substitution instances, a "tautology"

Selfcontradictory statement form:
A statement form that has only false substituion instances, a "contradiction"

Contingent Statement form:
A statement form that has both true and false substitution instances

Peirce's Law
 A tautological statement of the form:
 [(p _{horseshoe} q) _{horseshoe} p] _{horseshoe }p

Materially Equivalent:
A truth funcvtional relation asserting that two statements connected by the three bar sign have the same truth values

Biconditional Statement:
A compound statement that asserts that its two component statements imply one another and therefore are materially equivalent.

Logically equivalent:
two statements for which the statement of their material equivalence is a tautology; they are equivalent in meaning and can replace one another.

Double Negation:
An expression of logical equivalence between a symbol and the negation of the negation of that symbol.

De Morgan's Theorems
 1. the negation of the disjunction of two statements is logically equivalent to the conjunction ofthe negations of the two disjuncts
 2. The negation of the conjunction of two statements is logically equivalent to the disjunction of the negations of the two conjuncts

p (horseshoe) q is logically equivalent to:
 p v q

The three laws of thought:
 1. principle of identity
 2. principle of noncontradiction
 3. principle of excluded middle

Principle of identity:
if any statement is true, it is true

Principle of Noncontradiction:
 No statement can be both true and false
 Every state. of the form p dot p must be false. that every such state. is self contradictory

Principle of excluded middle:
 Every state. is either true or false
 Every state. of the form p v p must be true
 That every such state. is a tautology