Inductive vs. Deductive Reasoning

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.

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.

Deductive Reasoning

Deductive ReasoningFrom vague

To specific

A deductive argument

True Premise

True Premise

True Conclusion

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.

Inductive Reasoning The process of going from

observations to conclusions. This type of conclusion is

sometimes called an inference.

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

Inductive Reasoning

Inductive ReasoningFrom specific

To vague

A inductive argument

True Premise

True Premise

ProbablyTrue

Conclusion

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.

Let’s Practice –

Is the example Inductive Deductive

#1 Premise:

Everything made of copper conducts electricity.

Premise:

This wire is made of copper.

Conclusion: This wire will conduct electricity.

#2

Premise: Socrates was Greek.

Premise: Most Greeks eat fish.

Conclusion: Socrates probably ate fish.

#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.

#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.

#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.”

#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.