When you find the commonplaces of your audience and start your argument with something the audience already believes, you are using deductive logic.
Deductive logic in rhetoric starts with a general premise and moves on to the specific. It applies a fact (new appliances use less electricity) or a commonplace (energy-efficient appliances will save the environment) to a particular situation (buy a new appliance).
The general premise in deductive logic is the proof. The choice you want the audience to make is the conclusion. Rhetorical deduction uses facts or the commonplace beliefs of your audience for the proof and follows it with the choice you want them to make as the conclusion.
You’ll hear this rhetorical logic often when someone is trying to persuade you. Typically it takes the form of “We should (choice) because (commonplace).
“We should buy this software because it will make us more productive.”
“We should hire Joe instead of Bob because Joe went to our fraternity.”
What if you don’t have facts on your side and you can’t find a commonplace of the audience that works for you? Then you can use deductive logic’s opposite, inductive logic.
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