Lecture 11

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Logic & Critical Thinking

Session 1122 March, 2014

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The Dilemma• Dilemma is a common form of argument in ordinary language.• The Premises of the syllogisms are formulated disjunctively

(either-or) to trap the opponent by forcing him to accept one or the other of the disjuncts.

• Thus, the opponent is forced to accept the truth of the conclusion of one or the other of the syllogisms combined.

• When this is done successfully, the dilemma can prove to be a powerful instrument of persuasion.

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Contd….

• We say the person is “in” a dilemma (or impaled on the horns of a dilemma”) when that person must choose between two alternatives, both of which are bad or unpleasant.

• Three ways of evading the conclusion of dilemma have been given special names, all relating to the fact that a dilemma has two (or more) horns:– Going (or escaping) between the horns– Taking (or grasping) it by the horns– Rebutting it by the means of counterdilemma

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Going (or escaping) between the horns

• This is done by rejecting its disjunctive premise. • This method is the easiest way to evade the conclusion of a

dilemma.• There is a possibility that half disjunction is contradictory of

the other• E.G. giving higher marks to students will motivate them to

work harder. This can be criticized as:– If students are fond of learning they don’t need any stimulus– If students are not fond of learning no stimulus will be helpful

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Taking (or grasping) it by the horns

• When it is impossible to escape from the situation, one premise will have to be accepted while the other will be rejected.

• When we grasp the dilemma by the horns, we attempt to show that at least one of the conditionals are false.

• E.g to respond to “if students are fond of learning they need no stimulus”, the proponent may grasp the horns and say that even students who are fond of learning may sometimes need stimulus and that additional stimulus provided by marks promotes careful study by even most diligent students.

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Rebutting a Dilemma• To rebut a given dilemma, one constructs another dilemma whose

conclusion is opposed to the conclusion of the original.• Any counterdilemma may be used in rebuttal but ideally it should be

built up out of the same ingredients (categorical propositions) that the original dilemma contained:

• E.g – If you say what is just, men will hate you; and if you say what is

unjust, god will hate you. But you must say either the one or the other, therefore you will be hated

• Rebuttal – If I say what is just, god will love me; if I say what is unjust, men will

love me. I must say either the one or the other. Therefore, I shall be loved.

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Induction

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Two Basic Categories of Human Reasoning

• Deduction: reasoning from general premises, which are known or presumed to be known, to more specific, certain conclusions.

• Induction: reasoning from specific cases to more general, but uncertain, conclusions.

• Both deductive and inductive arguments occur frequently and naturally…both forms of reasoning can be equally compelling and persuasive, and neither form is preferred over the other (Hollihan & Baske, 1994).

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Example• Imagine eating a Malteaser• Its chocolatey• Imagine eating another few

Maltesers • They are also chocolatey.• So all Maltesers are chocolatey –

or, at least, the next one you eat will be

• That’s induction: Your experience has led to formulate a general conclusion

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Induction or Deduction?• For example, suppose you spend the weekend in a small

town and the first five people you meet are friendly, so you inductively conclude the following: "Everybody here is so nice.“

Induction

• "The victim died in the bathtub but was moved to the bed. But, neither woman could have lifted the body, nor could the butler with his war wound. Therefore, the business partner must have committed the crime.“

Deduction

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Why is Induction Important?• It is a valid form of argument

“We can expect the future to be like the past”

– We can have science– We can have prediction certainty.– We can formulate new principles about the world.– We can generalize about our experience on a secure

rational basis

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How Does Induction Work?• We use inductive arguments all the time.• But what is the basis of this use?• How can we be sure that induction is a valid kind of

argument?• Hume argues that we cannot. He suggests that there is no

rational case for induction being correct…

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Induction Flaw• It was David Hume that brought forth the Problem of

Induction in the 1700’s. The problem of induction is the philosophical question of whether inductive reasoning leads to knowledge. That is, what is the justification for either:

1. Generalizing about the properties of a class of objects based on some number of observations of particular instances of that class (for example, the inference that "all swans we have seen are white, and therefore all swans are white," before the discovery of black swans)

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Contd….

2. Presupposing that a sequence of events in the future will occur as it always has in the past (for example, that the laws of physics will hold as they have always been observed to hold). Hume called this the Principle of Uniformity of Nature.

3. If Hume’s conclusion, that science is irrationally grounded in custom and habit is correct, then we have to explain how scientific knowledge can be rational given the fact that it cannot rationally be justified.

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Hume: His view of the Consequences

• As soon as the suspicion is planted that the past is not a certain guide to the future, all experiences become useless and cannot rationally support any inference or conclusion.

• In all reasoning from experience, then, there is a step taken by the mind (that the future resembles the past) which is not supported by any rational argument.

• There must therefore be some other principle (than rational or demonstrative argument)

• This principle is custom….

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Summary• The basis of inductive reasoning about experience is our

experience of cause and effect.• From similar causes we get similar effects: The principle of

uniformity• The basis for the principle of uniformity is simple an inductive

argument• So rational arguments in support of induction assume what

they set out to prove.• Hence, there is no rational basis for our use of inductive

argument.

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Analogies

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Analogies• Analogies are comparisons of one item with or two others.

Analogies are used in three different ways.1. Analogies are used in descriptions: "Breakfast without orange juice is like a day without sunshine."2. In explanations: "Electrons in an atom are like planets in a solar system, and the nucleus is like the sun the planets orbit."3. In arguments: "My last car was a Honda. It gave me good gas mileage. I just bought a new Honda. It will probably give me good gas mileage, too."

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Criteria for Evaluating Analogies1. Number of entities being compared.

– The greater the number, the stronger the argument.– E.g. if you have more past experience, your analogy will be stronger. If

you purchased ice-cream from one shop 6 times, there is a possibility that the 7th time also the ice-cream will be of the desired standard.

2. Variety of instances in the premises.– The more dissimilar, the stronger the argument.– E.g. the brand of ice-cream was purchased at different instances from

shop A, B and C. Still, the taste is of the desired standard. This means there is nothing to do with the vendor but it is the manufacturer who Is making standard ice-cream.

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Criteria for Evaluating Analogies3. Number of respects.– The greater the number of respects, the stronger the

argument.– The analog will be stronger if the respect in which it is

being compared is uniform– E.g. the buyer only purchased chocolate ice-cream. He

always purchases the same brand from different vendors and gets the desired standard of taste.

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Contd….

4. Relevance of the properties in the premises to the properties in the conclusion.– The closer the relevance is to a causal connection, the

stronger the argument– E.g. If previously ice-cream was purchased on Tuesday,

it is not important that if the ice-cream will be purchased on Tuesday then only it will taste good. It is just the manufacturer which will affect the taste of the ice-cream. The day on which it is purchased or the clothes which you wear to purchase ice-cream from the shop will not affect the standard/taste.

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Contd….

5. Disanalogy: A disanalogy is a point of difference, a respect in which the case we are reasoning about out conclusion is distinguishable from the cases on which the argument is based.

• E.g. if the pair of shoes we plan to buy look like those we owned earlier, but is in fact much cheaper and made by a different company, those disanalogies will give us reason to doubt the satisfaction they will provide.

• For a better analogy always use similar instances for comparison. Disanalogies weaken the analogical arguments.

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Contd….

6. Claim that the conclusion makes: Every argument makes the claim that its premises give reasons to accept its conclusion. It is easy to see that the more one claims, the greater the burden of sustaining that claim, and that is obviously true for every analogical argument. – If a person gets 30 miles to the gallon from his new car, if I get the

same car, it will be modest to claim that I will be able to get atleast 25-28 miles from the gallon.

– In general, the more the modest the claim, the less burden is placed on the premises and the stronger the argument.

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Thank you