Induction and deduction are opposite forms of reasoning. Deduction is a type of formal logic in which you can arrive at a conclusion based on the truth of generalization. For instance, if all llamas are mammals, and Edgar is a llama, then you may deduce that Edgar is a mammal. Induction takes the opposite approach, arriving at a conclusion by way of a series of specific observations or premises. If Edgar has a long neck and two-toed hooves, has heavy, woolly fur, and comes from the Andes, you may infer, via induction, that he is a llama.

Start with a Question or Guess

In your introduction, pose a question or establish a hypothesis. May Flewellen McMillan, in her book on rhetoric, recommends this approach because it holds readers’ interest. As a researcher, you may begin with a question that you want to solve, but by the time you are writing the essay, you should know the answer. Posing the question is a rhetorical strategy. Having pre-planned your essay, you know that he is a llama, but begin by asking, “What kind of animal is Edgar?” You should already have an idea about Hamlet’s madness, but begin your essay by asking, “Is Hamlet truly mad or just pretending?”

Establish Specific Premises

Address the guiding question by building a series of premises. These are specific data points that address your question. The type of premises will depend on subject area. In sociology, for instance, a researcher might conduct case studies and draw the initial hypothesis from these observations, explains Gordon Marshall in the “Dictionary of Sociology.” A literature essay, on the other hand, presents observations about a character or theme. For instance, you should present your observations of Hamlet’s behavior, some of which (like his rash killing of Polonius) seems insane, and some of which (like his clever circumvention of Rosencrantz and Guildenstern’s plot) seems sane.

Make an Inductive Leap

Because induction draws a conclusion from a series of separate observations, it deals with probability, not certainty, according to David Naugle, philosophy professor at Dallas Baptist University. Deduction proceeds to a firm conclusion that cannot be disputed as long as the premises are sound. With induction, on the other hand, all the premises can still be true individually but not guarantee the result. Edgar can have a long neck, shaggy fur, divided hooves and come from the Andes and still not be a llama. While that is the likeliest conclusion, there is a chance that Edgar is a vicuña. The conclusion about what sort of animal Edgar is requires what rhetoricians call a “leap” in reasoning. It is a matter of probability, not certainty.

Defend the Conclusion

If you believe that your conclusion is supported, as much as possible, by the examples or observations, be explicit about this degree of certainty. Readers will only follow the inductive leap as far as it seems reasonable. You have to provide the reasoning that supports your inductive leap by which you arrived at your conclusion. If you conclude that Hamlet is sane, then spell out why his seemingly insane actions are the product of his craftiness. If you conclude that Hamlet is mad, then spell out how his seemingly sane actions could result from an unstable psyche or how they represent momentary bouts of clarity. You can present outside research to support your conclusions, such as prior studies done on the prevalence of llamas versus vicuñas or psychological analyses of unstable behavior that resembles Hamlet’s.