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Inductive vs. Deductive Reasoning
23

Inductive v. deductive

Nov 17, 2014

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JasonProff

A very detailed look at inductive vs. deductive reasoning.
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Page 1: Inductive v. deductive

Inductive vs. Deductive Reasoning

Page 2: Inductive v. deductive

Deductive Reasoning Starts with a general rule (a

premise) which we know to be true. Then, from that rule, we make a true conclusion about something specific.

Page 3: Inductive v. deductive

Deductive Reasoning The process of reasoning from known

facts to conclusions. When you reason deductively, you can say “therefore” with certainty. If your facts were firm to begin with, then your conclusions will also be firm.

Page 4: Inductive v. deductive

Deductive Reasoning

Page 5: Inductive v. deductive

Deductive ReasoningFrom vague

To specific

Page 6: Inductive v. deductive

A deductive argument is one in which it is impossible for the premises to

be true but the conclusion false. It is supposed to be a definitive proof of the truth of

the claim (conclusion). Premise All men are mortal. Premise Socrates was a man. Conclusion Socrates was mortal.

If the premises are true (and they are), then it simply isn't possible for the conclusion to be false.

If you have a deductive argument and you accept the truth of the premises, then you must also accept the truth of the conclusion.

Page 7: Inductive v. deductive

A deductive argument

True Premise

True Premise

True Conclusion

Page 8: Inductive v. deductive

Deductive Reasoning Example:

Smith owns only blue pants and brown pants. Smith is wearing a pair of pants today. So, Smith is wearing either blue or brown pants today.

Page 9: Inductive v. deductive

Inductive Reasoning The process of going from

observations to conclusions. This type of conclusion is

sometimes called an inference.

Page 10: Inductive v. deductive

Inductive Reasoning Observing that something is true

many times, then concluding that it will be true in all instances

Using the data to make a prediction

Page 11: Inductive v. deductive

Inductive Reasoning

Page 12: Inductive v. deductive

Inductive ReasoningFrom specific

To vague

Page 13: Inductive v. deductive

An inductive argument is one in which the premises are supposed to support the

conclusion. If the premises are true, it is unlikely that the conclusion

is false. The conclusion probably follows from the premises.

Premise Socrates was Greek. Premise Most Greeks eat fish. Conclusion Socrates ate fish.

Even if both premises are true, it is still possible for the conclusion to be false (maybe Socrates was allergic to fish).

Words which tend to mark an argument as inductive include probably, likely, possibly and reasonably.

Page 14: Inductive v. deductive

A inductive argument

True Premise

True Premise

ProbablyTrue

Conclusion

Page 15: Inductive v. deductive

Inductive Reasoning Example:

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

Page 16: Inductive v. deductive

Which conclusion below shows evidence of deductive reasoning?

A. One time an employee used store computers to download a harmful virus, so employee computer use is a security threat.

B. Many customers complained about employees using computers rather than working, so computer misuse was harming the company’s sales.

C. An employee on a break distracted other employees by using a computer in a public area for private business, so that employee was given a warning.

D. Several employees left customer sales information visible on computer screens, so those employees were instructed to always close windows with personal information.

Page 17: Inductive v. deductive

Let’s Practice –

The word wall is InductiveThe windows are Deductive

Page 18: Inductive v. deductive

#1 Premise:

Everything made of copper conducts electricity.

Premise:

This wire is made of copper.

Conclusion: This wire will conduct electricity.

Page 19: Inductive v. deductive

#2

Premise: Socrates was Greek.

Premise: Most Greeks eat fish.

Conclusion: Socrates probably ate fish.

Page 20: Inductive v. deductive

#3 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 robbed Wachovia Bank yesterday.

Page 21: Inductive v. deductive

#4 Premise: All

turtles have shells.

Premise: The animal I have captured is a turtle.

Conclusion: I conclude that the animal in my bag has a shell.

Page 22: Inductive v. deductive

#5Sherlock Holmes and Watson were on a camping trip. They had gone to bed and were lying there looking up at the sky. Holmes said, “Watson, look up. What do you see?”“I see thousand of stars.”“And what does that mean to you?”“I guess it means we will have another nice day tomorrow. What does it mean to you, Holmes?”“To me, it means someone has stolen our tent.”

Page 23: Inductive v. deductive

#6 Premise: Tonya is

seen walking from her car to her home with a set of golf clubs.

Premise: Tonya’s husband Jeff loves golf and tomorrow is his birthday.

Conclusion: Tonya has bought the set of golf clubs for Jack.