A Closer Look at Inductive vs. Deductive Reasoning

Deductive vs. Inductive Reasoning

• The difference:inductive reasoning uses patterns to

arrive at a conclusion (conjecture)

deductive reasoning uses facts, rules, definitions or properties to arrive at a conclusion.

• Inductive reasoning - Think of it like aWe start with specifics and move to

generalities

• Deductive reasoning – think of it like a We start with generalities and move to

specifics.

Examples of Inductive Reasoning

Some examples

1) Every quiz has been easy. Therefore, the test will be easy.

2) The teacher used PowerPoint in the last few classes. Therefore, the teacher will use PowerPoint tomorrow.

3) Every fall there have been hurricanes in the tropics. Therefore, there will be hurricanes in the tropics this coming fall.

Deductive Reasoning

The catalog states that all entering freshmen must take a mathematics placement test.

Conclusion: You will have to take a mathematics placement test.

You are an entering freshman.

An Example:

Inductive or Deductive Reasoning?

Geometry example…

60◦

x

Triangle sum property - the sum of the angles of any triangle is always 180 degrees. Therefore, angle x = 30°

What is the measure of angle x?

Inductive or Deductive Reasoning?

Geometry example…

What is the next shape in the sequence?

90% of humans are right handed. Joe is human, therefore Joe is right handed.

DEDUCTIVE

You are a good student.You get all A’sTherefore your friends must get all A’s too

INDUCTIVE

All oranges are fruits. All fruits grow on treesTherefore, all oranges grow on trees

DEDUCTIVE

Mikhail hails from Russia and Russians are tall, therefore Mikhail is tall

INDUCTIVE