LECTURE 3: REASONING AND LOGIC

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In our previous lecture we:In our previous lecture we:

1.1.Looked at the origins of philosophyLooked at the origins of philosophy

a)a) Investigated Thales’ metaphysical theory that everything is Investigated Thales’ metaphysical theory that everything is composed of water.composed of water.

b)b) Contrasted the rational thinking (Contrasted the rational thinking (logoslogos) of Thales with the ) of Thales with the mythical thinking (mythical thinking (mythosmythos) of his predecessors. ) of his predecessors.

1.1.Discussed in further detail the similarities and differences between Discussed in further detail the similarities and differences between science and philosophyscience and philosophy

2.2.Discussed the methodological differences between science and Discussed the methodological differences between science and philosophyphilosophy

3.3.Concluded by discussing the value of philosophyConcluded by discussing the value of philosophy

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Unresolved Discussions:Unresolved Discussions:

Q: Does ‘philosophy’ change over time?Q: Does ‘philosophy’ change over time?

Throughout its history, science has undergone numerous changesThroughout its history, science has undergone numerous changes

These changes have often had big influences on society, philosophy These changes have often had big influences on society, philosophy

etc.etc.

Possible answers include:Possible answers include:

RationalismRationalism

““The view that affirms The view that affirms reasonreason, with its interest in , with its interest in evidenceevidence, , examinationexamination, and , and evaluationevaluation, as authoritative in all matters of , as authoritative in all matters of

belief and conduct”belief and conduct”((Miller, Ed L. Questions that Matter, 2009. p.10))

Option 1: The discipline we call ‘Philosophy’ including its methods, scopes and aims, undergoes historical changes.

Option 2: Although there was once a time before philosophy, philosophy does not change.

Option 3: Some features of philosophy may change, but others do not.The question, then, is; what remains constant and what changes?

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Unresolved Discussions:Unresolved Discussions:

Q: Should we view religious texts and religions as based Q: Should we view religious texts and religions as based

on mythical or rational thinking?on mythical or rational thinking?

Points for discussion:Points for discussion:Some scientists might, for example, claim that religious belief is Some scientists might, for example, claim that religious belief is governed entirely by mythical thinking.governed entirely by mythical thinking.

The appeal to supernatural beings might suggest a mythical The appeal to supernatural beings might suggest a mythical dimension.dimension.

Some philosophers, anthropologists, sociologists, etc. have asked Some philosophers, anthropologists, sociologists, etc. have asked whether the distinction between mythical and rational thinking is valid. whether the distinction between mythical and rational thinking is valid. In particular they ask whether the distinction is culturally biased.In particular they ask whether the distinction is culturally biased.

Remember! Just because an account discusses God does not Remember! Just because an account discusses God does not necessarily make it mythical!necessarily make it mythical!

RationalismRationalism

““The view that affirms The view that affirms reasonreason, with its interest in , with its interest in evidenceevidence, , examinationexamination, and , and evaluationevaluation, as authoritative in all matters of , as authoritative in all matters of

belief and conduct”belief and conduct”((Miller, Ed L. Questions that Matter, 2009. p.10))

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Unresolved Discussions:Unresolved Discussions:

Q: Should we view religious texts and religions as based Q: Should we view religious texts and religions as based

on mythical or rational thinking? on mythical or rational thinking?

Possible answer: There are different ways of investigating the Possible answer: There are different ways of investigating the

same thingsame thing

For example, we could investigate the Bible in the following ways:For example, we could investigate the Bible in the following ways:

RationalismRationalism

““The view that affirms The view that affirms reasonreason, with its interest in , with its interest in evidenceevidence, , examinationexamination, and , and evaluationevaluation, as authoritative in all matters of , as authoritative in all matters of

belief and conduct”belief and conduct”((Miller, Ed L. Questions that Matter, 2009. p.10))

Mythically Philosophically Scientifically

The Bible is full of mythical narratives that explain our world. E.g. The story of Adam & Eve.

The Bible uses fables and stories to teach us valuable knowledge about how we should live.

Scientists might seek to find physical evidence that proves the truth of the Bible. E.g. Pieces of the Ark.

LOGIC AND REASONING

TODAY’S LECTURE

In today’s lecture we will:

1.1.Investigate an important tool used by philosophers: logic and Investigate an important tool used by philosophers: logic and reasoningreasoning

2.2.Examine the form of logicExamine the form of logic

3.3.Attempt to understand the distinction between Attempt to understand the distinction between Deductive and Deductive and Inductive Inductive reasoning.reasoning.

4.4.Outline and examine a number of important argumentative fallacies Outline and examine a number of important argumentative fallacies (invalid ways of arguing)(invalid ways of arguing)

5.5.Apply what we have learned using a number of examples.Apply what we have learned using a number of examples.

6.6.Conclude our investigation into the what/who/why/how of philosophy.Conclude our investigation into the what/who/why/how of philosophy.

Logic & How Not to ArgueLogic & How Not to Argue

Philosophers often use logic to examine and evaluate arguments:Philosophers often use logic to examine and evaluate arguments:

Logic is “The Formal Study of Valid Inferences”Logic is “The Formal Study of Valid Inferences”

Distinguishes between valid and invalid argumentsDistinguishes between valid and invalid arguments

Also distinguishes between Sound and Unsound argumentsAlso distinguishes between Sound and Unsound arguments

Powerful tool for analysis and criticism.Powerful tool for analysis and criticism.

Analyzes the logical structure of an argument (not the truth of Analyzes the logical structure of an argument (not the truth of

an argument)an argument)

LOGICAL AND REASONING

Two Forms of ReasoningTwo Forms of Reasoning

Deductive ReasoningDeductive Reasoning

In a valid deductive argument; if the premises are true, the In a valid deductive argument; if the premises are true, the conclusion must be true, by virtue of a logically necessary conclusion must be true, by virtue of a logically necessary inference.inference.

[Deductive arguments tend to argue from the whole to the particular][Deductive arguments tend to argue from the whole to the particular]

Inductive ReasoningInductive Reasoning

In a strong inductive argument: if the premises are true, the In a strong inductive argument: if the premises are true, the conclusion is probably true, by virtue of a supportive inference.conclusion is probably true, by virtue of a supportive inference.

[Inductive arguments tend to argue from the part to the whole][Inductive arguments tend to argue from the part to the whole]

LOGICAL AND REASONING((Miller, Ed L. Questions that Matter, 2008. p.23))

A little clarificationA little clarification

Valid ArgumentsValid Arguments

Valid Valid arguments display proper deductive formarguments display proper deductive form

True StatementsTrue Statements

True statements are possible in any argument regardless of True statements are possible in any argument regardless of formform

Sound ArgumentsSound Arguments

Sound arguments have both valid form and true premisesSound arguments have both valid form and true premises

LOGICAL AND REASONING((Miller, Ed L. Questions that Matter, 2008. p.19))

DEDUCTIVE REASONING

DEDUCTIVE REASONING

All men are mortal

Socrates is a man

Therefore Socrates is mortal

Premises

Conclusion

The premises logically entail the conclusion

The argument is valid and sound(Both true and logically valid)

Deductive Reasoning

DEDUCTIVE REASONING

An example of a deductive, logical argument

All A’s are B’s

S is an A

Therefore S is a B

Remember: If the premises of a deductive argument are

true the conclusion must be true!

DEDUCTIVE REASONING

Is this argument logically valid?

All ducks float on water

Professor Harris is a duck

Therefore Professor Harris floats on water

Do the premises logically entail the conclusion?

Is the argument true?

Is the argument sound? (is it logically valid and true?)

DEDUCTIVE REASONING

How about this one?

If it is raining then the streets are wet

The streets are wet

Therefore it is raining

Do the premises logically entail the conclusion?

Is the argument true?

Is the argument sound? (is it logically valid and true?)

INDUCTIVE REASONING

INDUCTIVE REASONING

An example of an inductive, argumentAn example of an inductive, argument

Instance 1 of A is observed to be XInstance 1 of A is observed to be X

Instance 2 of A is observed to be XInstance 2 of A is observed to be X

Instance 3 of A is observed to be XInstance 3 of A is observed to be X

Instance 4 of A is observed to be XInstance 4 of A is observed to be X

Instance 5 of A is observed to be XInstance 5 of A is observed to be X

......

Therefore, all A is XTherefore, all A is X

INDUCTIVE REASONING

An example of inductive reasoning: Universal

Generalization

Swan 1 is whiteSwan 1 is white

Swan 2 is whiteSwan 2 is white

Swan 3 is whiteSwan 3 is white

Swan 4 is whiteSwan 4 is white

Swan 5 is whiteSwan 5 is white

Swan 526 is whiteSwan 526 is white

...

Therefore all swans are whiteDo the premises give supportive inference to the conclusion?

Is the argument true?

Is the argument sound? (is there sufficient supportive inference and is the argument true?)

INDUCTIVE REASONING

Another example of inductive reasoning: Another example of inductive reasoning: AnalogyAnalogy

A is observed to be X and YA is observed to be X and Y

B is observed to be X and YB is observed to be X and Y

C is observed to be X and YC is observed to be X and Y

D is observed to be X and YD is observed to be X and Y

......

M is observed to be XM is observed to be X

Therefore, M is YTherefore, M is Y

Do the premises give supportive inference to the conclusion?Do the premises give supportive inference to the conclusion?

Is the argument true?Is the argument true?

Is the argument sound? (is there sufficient supportive inference Is the argument sound? (is there sufficient supportive inference and is the argument true?)and is the argument true?)

SUMMARY

Deductive Reasoning Inductive Reasoning

Argues from the Whole to the Particular

Argues from the particular to the whole

If the argument is valid and the premises are true; the conclusion MUST be true.

If the argument is sound and the premises are true; the conclusion

MIGHT be true.

Deductive arguments are only concerned with FORM (An argument may be logically valid but still false)

Inductive arguments rest on ‘supportive inferences’

Doesn’t teach us anything new Teaches us new things

Deductive ReasoningDeductive Reasoning

In a valid deductive In a valid deductive argument; if the argument; if the premises are true, premises are true, the conclusion must the conclusion must be true, by virtue of a be true, by virtue of a logically necessary logically necessary inference.inference.

Inductive ReasoningInductive Reasoning

In a strong inductive In a strong inductive argument: if the argument: if the premises are true, premises are true, the conclusion is the conclusion is probably true, by probably true, by virtue of a supportive virtue of a supportive inference.inference.

Valid ArgumentsValid Arguments

ValidValid arguments arguments display proper display proper deductive formdeductive form

True StatementsTrue Statements

True statements are True statements are possible in any possible in any argument regardless argument regardless of formof form

Sound ArgumentsSound Arguments

Sound arguments Sound arguments have both valid form have both valid form and true premisesand true premises

LOGICAL FALLACIES

Some more clarificationSome more clarification

Formal FallaciesFormal Fallacies

Mistakes in reasoning due to a failure in following the rules for Mistakes in reasoning due to a failure in following the rules for the formal structure of valid arguments. These fallacies do not the formal structure of valid arguments. These fallacies do not concern truth or falsity but validity.concern truth or falsity but validity.

Informal FallaciesInformal Fallacies

Mistakes in reasoning due to carelessness regarding relevance Mistakes in reasoning due to carelessness regarding relevance and clarity of language. These fallacies bear directly on issues and clarity of language. These fallacies bear directly on issues of truth and falsity.of truth and falsity.

LOGICAL FALLACIES((Miller, Ed L. Questions that Matter, 2008. p.23))

Argumentative FallaciesArgumentative Fallacies

1.Loaded Language is language with the sole purpose of swaying the emotions of the audience for or against an argument.

2.Equivocation occurs when a word or expression changes its meaning in the course of an argument, sometimes referred to as a “weasel word.”

3.Begging the Question occurs when the conclusion of an argument is already present, usually disguised, in one of its premises.

4.Ad Hominem (appeal to the person) irrelevantly attacks the person making a claim rather than attacking the claim itself.

5.Straw Man Inappropriately simplifies an opposing argument so that it becomes a cartoon or caricature of the true argument and is easy to refute.

6.“Person who” is the fallacy of generalizing or drawing a conclusion from too little information. Also called a hasty induction.

7.Ad populam (appeal to the masses) seeks to strengthen a claim by an emotional appeal to the passions and prejudices of the listeners.

8.Ad ignorantium (appeal to ignorance) affirms the truth of something on the basis of the lack of evidence to the contrary.

9.False Dilemma involves limiting the options considered to only two in a way that is unfair to the person facing the dilemma.LOGICAL FALLACIES

((Miller, Ed L. Questions that Matter, 2008. pp. 22-24))

TOPIC CONCLUSION

TOPIC CONCLUSION

What is Philosophy?What is Philosophy?

A rational investigation into a range of topics and aspects of human A rational investigation into a range of topics and aspects of human existenceexistence

Who does Philosophy?Who does Philosophy?

Everyone, particularly anyone that asks philosophical questions.Everyone, particularly anyone that asks philosophical questions.

Why do we do Philosophy?Why do we do Philosophy?

Many philosophical inquiries are important. Not everything can be Many philosophical inquiries are important. Not everything can be investigated scientifically.investigated scientifically.

Philosophy can provide us with important skills and knowledge.Philosophy can provide us with important skills and knowledge.

How do we do Philosophy?How do we do Philosophy?

Philosophers use reason and rational thinking as their principle means of Philosophers use reason and rational thinking as their principle means of conducting their inquiries; including logic; arguments; discussion; conducting their inquiries; including logic; arguments; discussion; observation; evaluation and more...observation; evaluation and more...

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Conclusions: Conclusions:

I.I. Some questions do not have any definite answers but are still valid Some questions do not have any definite answers but are still valid

questions!questions!

II.II. Philosophy can be useful tool for critically examine the assumptions Philosophy can be useful tool for critically examine the assumptions

implicit in other systems of thought.implicit in other systems of thought.

III.III. Philosophy is a useful tool for examining the world. (beyond the Philosophy is a useful tool for examining the world. (beyond the

natural sciences.natural sciences.

IV.IV. Like any tool, Philosophy has a limited role and application.Like any tool, Philosophy has a limited role and application.

UPCOMING TOPICS

Over the coming weeks we will be investigating:Over the coming weeks we will be investigating:

1.1.What is Reality? (Metaphysics/Ontology)What is Reality? (Metaphysics/Ontology)

(a) What is the relationship between mind and body?(a) What is the relationship between mind and body?

2.2.Theory of Knowledge (Epistemology)Theory of Knowledge (Epistemology)

3.3.Natural TheologyNatural Theology

4.4.Moral PhilosophyMoral Philosophy

TOPIC CONCLUSION

Perhaps ‘Philosophy’ Consists of “Family Resemblances”Perhaps ‘Philosophy’ Consists of “Family Resemblances”

And we can go through many, many other groups of games in the same And we can go through many, many other groups of games in the same

way; can see how similarities crop up and disappear.way; can see how similarities crop up and disappear.

And the result of this examination is: we see a complicated network of And the result of this examination is: we see a complicated network of

similarities overlapping and criss-crossing: sometimes overall similarities overlapping and criss-crossing: sometimes overall

similarities, sometimes similarities of detail.similarities, sometimes similarities of detail.

I can think of no better expression to characterize these similarities I can think of no better expression to characterize these similarities

than “family resemblances”: for the various resemblances between than “family resemblances”: for the various resemblances between

members of a family: build, features, colour of eyes, gait, temperament, members of a family: build, features, colour of eyes, gait, temperament,

etc. etc. overlap and criss-cross in the same way.—And I shall say etc. etc. overlap and criss-cross in the same way.—And I shall say

“games” form a family.“games” form a family.

Ludwig Wittgenstein, Ludwig Wittgenstein, Philosophical Investigations, Philosophical Investigations, (New York: Macmillan, 1964), p.32(New York: Macmillan, 1964), p.32

DISCUSSION

DISCUSSION

Questions for Discussion:Questions for Discussion:

1.1.Is the distinction between mythical and rational thinking valid? Or Is the distinction between mythical and rational thinking valid? Or

does modern science constitute another form of myth-making?does modern science constitute another form of myth-making?

2.2.Could science do without philosophy or vice versa?Could science do without philosophy or vice versa?

3.3.Defend one of these views:Defend one of these views:

a)a) ““Philosophy” can be defined.Philosophy” can be defined.

b)b) ““Philosophy” cannot be defined.Philosophy” cannot be defined.

4.4.Is philosophy a worthwhile subject?Is philosophy a worthwhile subject?

5.5.What is significant about the form of deductive arguments?What is significant about the form of deductive arguments?