Mental Models: Deduction and Induction

The scientific method is based on logical reasoning. When you draw conclusions that support evidence gathered in an investigation, you are following logic. Two methods of reasoning that are involved in logic are inductive and deductive reasoning.

Inductive reasoning involves drawing a conclusion by moving from specific observations to general ones. Deductive reasoning, on the other hand, involves drawing conclusions by applying a generalization to a specific example.

In the Complete Idiot's Guide to Writing Well, Laurie Rozakis says:

“Inductive reasoning draws a logical conclusion from specific facts. It depends on drawing inferences from particular cases to support a generalization or claim. Many of our everyday conclusions are based on inductive reasoning. For example, if three people whose judgment you respect tell you that a particular movie is worth seeing, you'll conclude that the movie is most likely something you'll enjoy.

Therefore, the success of an essay built inductively depends on the strength of your examples….

Deductive reasoning moves in the opposite direction, from a general premise to particular conclusions. Sometimes it depends on a logical structure called a syllogism. Here is an example:

Major premise: All men are mortal.
Minor premise: Herman is a man.
Conclusion: Therefore, Herman is a mortal.

If you accept the major premise that all men will eventually kick the bucket and the minor premise that Herman is a man, then you have to accept the conclusion. Most written arguments collapse because the major premise isn't true.”

An example of an inductive argument:
5+7=12 and twelve is an even number. Therefore, an odd number added to another odd number will result in an even number.

Inductive reasoning can be strong or weak. A strong induction is thus an argument in which the truth of the premises would make the conclusion probable, but not necessarily guarantee it as being factual. In weak induction the logical means of connecting the premise and conclusion are faulty.