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 a We 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 Every quiz has been easy. Therefore, the test will be easy. The teacher used PowerPoint in the last few classes. Therefore, the teacher will use PowerPoint tomorrow. Every fall there have been hurricanes in the tropics. Therefore, there will be hurricanes in the tropics this coming fall.

Deductive Reasoning An Example: The catalog states that all entering freshmen must take a mathematics placement test. You are an entering freshman. Conclusion: You will have to take a mathematics placement test.

Inductive or Deductive Reasoning? Geometry example… 60◦ x What is the measure of angle x? Triangle sum property - the sum of the angles of any triangle is always 180 degrees. Therefore, angle x = 30°

Inductive or Deductive Reasoning? Geometry example… What is the next shape in the sequence?

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

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

DEDUCTIVE All oranges are fruits. All fruits grow on trees Therefore, all oranges grow on trees DEDUCTIVE

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

Inductive vs Deductive Reasoning YouTube Video

Determine whether each conclusion is based on inductive or deductive reasoning.   Aundrea noticed that every Saturday, her neighbor mows his lawn. Today is Saturday. Aundrea concludes her neighbor will mow his lawn. Students at Blake’s high school must have a B average in order to participate in sports. Blake has a B average, so he concludes that he can participate in sports at school. At Uriah’s school if you are late five times, you will receive a detention. Uriah has been late to school five times; therefore he will receive a detention.

A dental assistant notices a patient has never been on time for an appointment. She concludes that the patient will be late for her next appointment.   If Cooper decides to go to a concert tonight, he will miss football practice. Tonight, Cooper went to a concert. Cooper missed football. Whenever Nicole has attended a tutoring session she notices that her grades have improved. Nicole attends a tutoring session and she concludes her grades will improve. Every Wednesday Kelsy’s mother calls. Today is Wednesday, so Kelsy concludes her mother will call.

Inductive Reasoning or Deductive Reasoning   1. No mayten tree is deciduous, and all nondeciduous trees are evergreens. It follows that all mayten trees are evergreens. Deductive 2. Mike must belong to the Bartenders and Beverage Union Local 165, since almost every Los Vegas bartender does. Inductive 3. Either Colonel Mustard or Reverend Green killed Professor Plum. But whoever ran off with Mrs. White did not kill the professor. Since Reverend Green ran off with Mrs. White, Colonel Mustard killed Professor Plum. 4. I’ve never met a golden retriever with a nasty disposition. I bet there aren’t any. 5. Since some grapes are purple, and all grapes are fruit, some fruit is purple.

6. Why is Sarah so mean to Janice 6. Why is Sarah so mean to Janice? The only thing I can think of is that she’s jealous. Jealousy is what’s making her mean. Inductive 7. Obama will make a fine president. After all, he made a fine senator. 8. The figure he drew has only three sides, so it isn’t a square. Deductive 9. It was the pizza that made my stomach churn. What else could it be? I was fine until I ate it. 10. It’s wrong to hurt someone’s feelings, and that is exactly what you are doing when you speak to me like that.  Deductive