deduction and induction.pptx

7/30/2019 Deduction and Induction.pptx

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Evaluating DeductiveArgumentsCHAPTER 6


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DeductionandInduction


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All arguments claim to provide

support- that is, evidence orreasons- for their conclusions.

Traditionally, arguments havebeen divided into two types:

1. Deductive Argument

2. Inductive Argument


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DEDUCTIVE ARGUMENT

conclusions of these arguments are

established by the premises with

absolute certainty.

each conclusion flows from its

premises with logical necessity.

This means that, given the premises, theconclusion could not be possibly false.


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DEDUCTIVE ARGUMENT

Examples:

All crustaceans are arthropods.

All spiders are arthropods.Therefore, all spiders are crustaceans.

Quartz scratches glass.

Therefore, quartz is harder than glass.


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Examples:

If the sun is starAnd sun has planets

Therefore, some stars have planets

All men are mortal

Socrates was a man

Socrates was mortal


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INDUCTIVE ARGUMENTS

simply claim that their conclusions arelikely or probable given the premisesoffered.

Example:

Maria has good study habits and is alwaysattentive in class discussions.

She is a consistent deans lister and has neverfailed in any subject she has taken.

Therefore, it is very probable that Maria will not failin her P-101 class.


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Examples:

Socrates was Greek

Most Greeks eat fish

Socrates ate fish

You have a very good friend circle

Therefore, you are very good


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INDUCTIVE ARGUMENTS

Truth of the premises cannotabsolutely rule out the possibility

that the conclusion will be false.

In other words, the conclusion might

turn out to be false even thepremises are true.


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INDUCTIVE ARGUMENTS

Example:

The car cant start even though there is

plenty of gasoline in the tank.

It is likely that the battery is already

exhausted.


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It is sometimes said that the basic

difference between deduction andinduction is that:

INDUCTION moves from particularpremises to general conclusions.

DEDUCTION moves from generalpremises to particular conclusions.


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Examples:

DEDUCTION

Three is a prime number.

Five is a prime number.

Seven is a prime number.

(particular premise)

Therefore, all odd numbers between two and eight areprime numbers.

(general conclusion)

INDUCTION

All ofJ.K.Rowlings previous books have been bestsellers.(general premise)

Therefore, her next book will probably ba a bestseller.

(particular conclusion)


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Differences Between

Deductive and Inductive Reasoning

Deductive Arguments

claim that

Inductive Arguments

claim that

If the premises are

true, then theconclusion is certainlytrue.

The conclusion followsnecessarily from thepremises.

If the premises are

true, then theconclusion isprobably true.

The conclusion followsprobably from thepremises.


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Differences Between

Deductive and Inductive Reasoning

Deductive Arguments

claim that

Inductive Arguments

claim that

The premises provide

conclusive evidencefor the truth of theconclusion.

The truth of thepremises guaranteesthe truth of theconclusion.

The premises provide

good evidence for thetruth of theconclusions.

The truth of thepremises makes thetruth of the conclusionlikely.


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To determine whether an argument isdeductive or inductive, here are some

common indicator words:

certainly

definitelyabsolutely

conclusively

it is logically to conclude thatthis logically implies thatthis entails that

it must be the case that

DEDUCTIVEINDICATOR WORDS


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probably

likelychances are

one would expect that

it is plausible to support thatit is reasonable to presume that

INDUCTIVE INDICATOR

WORDS


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When no indicator words are

present to help us decidewhether an argument is

deductive or inductive, we just

have to base our judgmentonthe content of the premises

and conclusion of the

argument.


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THANK YOU FORLISTENING!!!

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