Flashcards in Unit 1 Deck (33)

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## Logic

### Study of methods for evaluating arguments

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## Argument

### set of statements, one of which, called the conclusion, is affirmed on the basis of the others, which are called the premises

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## Statement

### sentence that is either true or false

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## True Values

### truth and falsehood are the two possible outcomes

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## Premises

### the statements on the basis of which the conclusion is affirmed

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## Conclusion

### the statement that is affirmed on the basis of the premises

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## Valid argument

### it is necessary that if the premises are true, then the conclusion is true

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## Invalid argument

### It is not necessary that if the premises are true, then the conclusion is true

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## Sound Argument

### It is valid and all its premises are true

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## Unsound Argument

### Is an argument that either is invalid or has at least one false premise

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## deductive logic

### Part of Logic that is concerned with tests for validity and invalidity

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## Substitution Instance

### an argument that results from uniformly replacing letters with terms in an argument

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## Argument form

### pattern of reasoning

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## Counterexample

### Is a substitution instance whose premises are well known truths and whose conclusion is a well-known falsehood

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## Antecedent

### the if-clause of a conditional

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## Consequent

### the then-clause of a conditional

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## logically equivalent

### two statements are this if each validity implies the other

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## 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.

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## 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.

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## Negation

### Denial

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## Fallacy of denying the antecedent

###
If A, then B.

Not A.

Therefore, Not B.

invalid and is confused with modus tollens

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## Fallacy of affirming the consequent

###
If A, then B.

B.

Therefore, A.

invalid and is confused with modus ponens

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## 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.

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## disjunctions

### statements of the form "either A or B"

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## 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).”

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## 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

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## Strong Argument

### It is probable (but not necessary), that if the premises are true, then the conclusion is true

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## Weak argument

### It is not probable that if the premises are true, then its conclusion is true

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## Arguments from authority

###
R is a reliable authority regarding S

R sincerely asserts that S.

So S

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