Deductive and Inductive Reasoning

Key Terms…

Deductive- an argument whose conclusion is certain

Inductive- an argument whose conclusion is likely

Premise- a reason offered as support for a claim

Syllogism- a form of deductive reasoning consisting of a major premise, a minor premise, and a conclusion.

Deductive Reasoning

Deductive Reasoning – A type of logic in which one goes from a general statement to a specific instance.

The classic exampleAll men are mortal. (major premise)

Socrates is a man. (minor premise)

Therefore, Socrates is mortal. (conclusion)

Deductive Reasoning

Examples:1. All students eat pizza.

Claire is a student at ASU.Therefore, Claire eats pizza.

2. All athletes work out in the gym. Barry Bonds is an athlete. Therefore, Barry Bonds works out in the

gym.

Let’s try one…

Smith owns only blue and brown pants. Smith is wearing a pair of his pants today. Therefore…

This is a deductive argument because the first two premises prove the last sentence must be true.

The soccer game is either on Thursday or Friday.

I just found out that the game is not on Thursday.

So the game must be on __________

Is this deductive?

Inductive Reasoning

Inductive Reasoning, involves going from a series of specific cases to a general statement. The conclusion in an inductive argument is never guaranteed.

Example

All men are messy.(–premise) Mr. Southworth is a man.(– premise) Therefore Mr. Southworth must be

messy. (--conclusion)

BUT NOT NECESSARILY!!! The argument is valid, but certainly not true. It’s based on a false premise. Be careful with false premises when using logic

January is cold in Siberia. Today is January 14. It will be another cold day in Siberia.

This argument is inductive. It is likely but not guaranteed.

The local branch of Wachovia Bank was robbed yesterday. Jenny needed money to pay off her debts. She just bought a gun two days ago, and I saw her hanging around the local Wachovia bank yesterday morning. Today the people she owed money to stopped looking for her. So Jenny must have robbed that bank.

If you have ever seen an episode of Law & Order you know that they prove issues like this to be wrong so this is _______ reasoning.

Deductive (based on laws, rules, & things known):

All dogs are mammals. All mammalshave kidneys. Therefore, all dogs havekidneys.

Inductive (based on an observation):

All dogs that we have seen are white;therefore the next dog we see will bewhite.

Deductive (based on facts, laws, rules):

All squares are rectangles and allrectangles have four sides. So all squaresmust have four sides.

Inductive (based on observations):

Since Chris is a good athlete, and there are good athletes in his family. His sister

must be a good athlete, too.

Emily’s shirt is red. My’kia is wearing a

red shirt. Malik’s shirt is also red.

Therefore, the next person I see will be

wearing a red shirt.

According to the LMS discipline policy, if a student is disrespectful to a teacher, they receive a dean referral. Anthony was disrespectful to his teacher, so he will receive a dean referral.

Women hate sports. Mrs. Southworth is a woman.

She must hate sports.

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