- StudyBlue
- Washington
- Western Washington University
- Philosophy
- Philosophy 102
- Daniel/howard-snyder
- Logic Chapter 1

Alex L.

Logic

the study of methods for evaluating whether the premises of an argument adequately support its conclusion

Argument

a set of statements where some statements, called PREMISES, are intended to support another, called the CONCLUSION

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Statement

a sentence that is either true or false

Deductive Argument

premises are intended to guarentee the conclusion

Inductive Argument

the premises are intended to make the conclusion more PROBABLE, without guaranteeing it

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

a valid argument in which all of the premises are true

Unsound Argument

is either invalid or has at least one false premise

Argument Form

a pattern of reasoning

Modus Ponens

If A, then B.

A.

So B.

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Substitution Instance

an argument that results from uniformly replacing the variables in that form with statements (or terms)

Valid argument form

a form in which every substitution instance is a valid argument

Formally Valid Argument

an argument that is valid in virtue of its form

Conditional Statement

- contains an antecedent and a consequent (an if-then statement)

Antecedent

the if-clause of a conditional statement

Consequent

the then-clause of a conditional statement

Stylistic Variants

alternate ways of saying the same thing

- i.e. "given that, assuming that, if, etc."

Modus Tollens

If A, then B.

Not B.

So, Not A

Negation

the denial of a statement

- i.e. "Not A, it is not the case that, it's false that, it is not true that, etc"

Hypothetical Syllogism

If A, then B.

If B, then C.

So, If A, then C

Disjunctions

statements of the form "Either A or B"

- each part is called a "disjunct"

Disjunctive Syllogism

EIther A or B

Not A

So, B

(A and B can be interchanged in the second and third premise, as long as it remains constant)

- ASSUME THAT statements of the form 'Either A or B' mean 'Either A or B (or Both)'

Constructive Dilemma

Either A or B.

If A, then C.

If B, then D.

So, either C or D.

- this form combines both conditional and disjunctive statements

Famous Forms Method

checking to see whether the argument made is a form on the famous list; if it is, it is valid

- some valid forms are not famous
- does not show invalidity

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