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# It’s Logical - PowerPoint PPT Presentation

It’s Logical. Deductive and Inductive Reasoning. What is Logic?. Logic – The science of correct reasoning. Reasoning – The drawing of inferences or conclusions from known or assumed facts . There are two main types of reasoning: Deductive Inductive. Deductive Reasoning.

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### It’s Logical

Deductive and Inductive Reasoning

• Logic – The science of correct reasoning.

• Reasoning– The drawing of inferences or conclusions from known or assumed facts.

• There are two main types of reasoning:

• Deductive

• Inductive

• Deductive reasoning is a method of drawing conclusions from premises based upon fact.

• The conclusions reached are mostlycertain, inevitable, inescapable as long as it is within logical bounds.

• Goes from a general statement to a specific instance.

• The structure of a deductive argument is very important to prove its validity. This is called a syllogism.

• Standard Structure: Ifthe premises are true, thenthe conclusion is necessarily true.

• Deductive reasoning does not grant new knowledge, but clarifies concepts that we already know about.

• It aims to produce true, valid conclusions but is dependent on experience with and prior knowledge of the premises.

• Examples:

• All men are mortal. (general) FACTSocrates is a man. (specific) FACTTherefore, Socrates is mortal. (conclusion)

• All high school students are teenagers. Claire is a high school student.Therefore, Claire is a teenager.

• Are there any other conclusions you could possibly come to given this information?

• Some dogs are ill-behaved.Dogs are animals.Therefore, animals are ill-behaved.

• Athletes work out.Michael Jordan is an athlete.Therefore, _______________________________.

• Musicians are crazy.Madonna is a musician.Therefore, _______________________________.

• You create one!

• You create one!

• Inductive reasoning is a method of drawing conclusions based upon limited information.

• The conclusions reached are probable, reasonable, plausible, believable.

• Analogies and statistics are the basic forms of this type of argument.

• Goes from a series of specific cases to a general statement.

• Is a sophisticated replacement for the word “guessing”!

• Inductive reasoning is useful for gaining knowledge by understanding statistical patterns and identifying causes and effects.

• The terms valid and invalid cannot be accurately applied to inductive reasoning—only likely and unlikely.

• Inductive arguments cannot guarantee true conclusions even if the premises are true.

Inductive REasoning

• Examples:

• Some horses are big.All horses have tails.Therefore everything that has a tail is big.

• What number comes next in this sequence? 2, 4, 6, 8, 10

• John just bought a car. His favorite color is blue. What color is John’s car?

• Do you KNOW the answers or do you ASSUME the answers?

• Tell whether the following arguments use inductive or deductive reasoning:

• All turtles eat vegetables. Betsy is a turtle. Betsy eats vegetables.

• Biff has a tattoo of an anchor on his arm. It is known that Sailors often get nautical tattoos.He probably served in the Navy.

• January has always been cold here in Siberia. Today is January 14, so it is going to be another cold day here.

• I knew the soccer game was on either Thursday or Friday. I just found out that it was not on Thursday, so the game must have been on Friday.

• All 15 of Ty’s cats like to play with yarn. He just adopted a new kitten and he is sure that she will definitely enjoy playing with yarn.

A sample of fifty drivers who were stopped by at a sobriety checkpoint on a Saturday at midnight revealed that one in four drivers were either uninsured, intoxicated, or both. Thus, if you get involved in an accident on the freeway there is a 25% chance the other motorist will be drunk or uninsured.

The local branch of Wachovia Bank was robbed yesterday. Jenny needed money to pay off her gambling debts. She just bought a gun two days ago, and I saw her hanging around the local Wachovia Bank yesterday morning. Today the bookie’s goons stopped looking for Jenny. So Jenny definitely robbed Wachovia Bank yesterday.

• http://factchecked.org/2007/lesson-plans/house-and-holmes-a-guide-to-deductive-and-inductive-reasoninghttp://factchecked.org/2007/lesson-plans/house-and-holmes-a-guide-to-deductive-and-inductive-reasoning/

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