Unit 1 Flashcards
Logic
Study of methods for evaluating arguments
Argument
set of statements, one of which, called the conclusion, is affirmed on the basis of the others, which are called the premises
Statement
sentence that is either true or false
True Values
truth and falsehood are the two possible outcomes
Premises
the statements on the basis of which the conclusion is affirmed
Conclusion
the statement that is affirmed on the basis of the premises
Valid argument
it is necessary that if the premises are true, then the conclusion is true
Invalid argument
It is not necessary that if the premises are true, then the conclusion is true
Sound Argument
It is valid and all its premises are true
Unsound Argument
Is an argument that either is invalid or has at least one false premise
deductive logic
Part of Logic that is concerned with tests for validity and invalidity
Substitution Instance
an argument that results from uniformly replacing letters with terms in an argument
Argument form
pattern of reasoning
Counterexample
Is a substitution instance whose premises are well known truths and whose conclusion is a well-known falsehood
Antecedent
the if-clause of a conditional
Consequent
the then-clause of a conditional
logically equivalent
two statements are this if each validity implies the other
Modus Ponens
If A, then B.
A.
Therefore, B.
means “the mode of positing” (sometimes called the way of affirmation) because the second premise posits the antecedent of the conditional (first) premise.
Modus Tollens
If A, then B.
Not B.
Therefore, not A.
means “the mode of removing” (sometimes called “way of denial”) because the second premise removes or denies the truth of the consequent of the first (conditional or major) premise.
Negation
Denial
Fallacy of denying the antecedent
If A, then B.
Not A.
Therefore, Not B.
invalid and is confused with modus tollens
Fallacy of affirming the consequent
If A, then B.
B.
Therefore, A.
invalid and is confused with modus ponens
hypothetical syllogism
If A, then B.
If B, then C.
Therefore, If A, then C.
In Greek, “syllogism” means “to reason together.”
The argument is called “hypothetical” because it involves only conditional statements.
disjunctions
statements of the form “either A or B”
disjunctive syllogism
Either A or B.
Not A.
Therefore, B.
The two parts of the major premise are called “disjuncts.”
There are two senses of “or.”
The inclusive sense basically means “at least one of A or B (or both).”
The exclusive sense means “either A or B (but not both).”
constructive dilemma
Either A or B. If A, then C. If B, then D. So, either C or D. combines both conditional and disjunctive statements
Strong Argument
It is probable (but not necessary), that if the premises are true, then the conclusion is true
Weak argument
It is not probable that if the premises are true, then its conclusion is true
Arguments from authority
R is a reliable authority regarding S
R sincerely asserts that S.
So S
Arguments from analogy
Object A is similar to object B in certain relevant respects
B has property P
So A has property P also
Cogent argument
any argument that is both strong and has only true premises
Uncogent argument
is either weak or strong but has one or more false premise.
Inductive logic
part of logic that concerns tests for strength and weakness
