Deductive logic interprets the circumstances through an existing audience belief. It uses this commonplace belief to reach a conclusion, a decision or an action that you want your audience to make.

Give your children the best education possible by sending them to the finest high school in the city, Green Meadows Prep.

The audience of parents who might send their children to private school holds the commonplace belief that giving their children the best education is important. Green Meadows school leads them to conclude that Green Meadow is the way to provide their children an excellent education.

But what if Green Meadows wants to recruit promising children from neighborhoods that have not had the economic means or the cultural history of sending their children to private school? The school can remove the economic obstacle with a financial aid program. But Green Meadow still has to convince families of the benefit of their school when these families don’t already possess commonplace beliefs about the value of a private school education.

These families may not see the value of preparing children for college if they expect children to work in the family business. Or they may be concerned about the moral environment of a school they aren’t familiar with. Or perhaps they are concerned that their children would drift away and their families would break apart.

They’re all valid concerns. Green Meadow must address them if they want to recruit these families.

When your audience doesn’t have commonplaces that lead to the conclusion you want them to make, then it’s time to switch from deductive logic to inductive logic.

Inductive logic is argument by example. Your examples form your proof. Instead of going from the general to the specific, you are going from specific examples to a general conclusion. Since your audience doesn’t already possess an existing belief, you use the circumstances to help them form a belief.

Examples can include facts, comparisons, or story. Facts and comparisons are useful on many occasions, but story is by far the most powerful example. Why? Because your story lets the audience simulate the experience of the action you want them to take. It’s almost as good as if they actually had the experience.

How would this work for Green Meadow School? They could use examples to help the audience form the same belief that their existing parents have, “give your children the best education possible.”�

Facts and Comparisons: Green Meadow could make claims like these: “Children who get a private school education make more money and have a lower incidence of drug use and teen pregnancy.”

Story: Here the school can tell a few stories of families like those of the audience who sent their children to Green Meadow, students who encountered some obstacles but were able to overcome them. Their story can include the ways that the school supported those students, both inside and outside the classroom. The story can span the students’ successful transition to college and their continued strong relationships with their families.

By this time some families may be coming around to the belief in an excellent education and have reached the conclusion that Green Meadow can make it happen. The school has successfully used a few examples to show how an excellent education is advantageous to their audience of skeptical parents.

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.

Your logical argument begins with something the audience already believes or wants. To shift their opinion you have to start with where they are today. Find out what they are thinking by looking for the common place, the viewpoints that your audience holds in common.

A commonplace is simply a shorthand expression of common sense or opinion. Commonplaces in business include “serving the customer,”� “investing resources wisely,”� “hiring the best people,”� and “managed earnings.”�

In technical industries you hear commonplaces like:

• Burn the boats (taking a risk, putting yourself in a position where you have no choice but to succeed)
• Eat their young (creative destruction, an economic theory of innovation and progress)
• The innovator’s dilemma (product lines cannot simultaneously serve (1) high-profit customers who will pay a premium for product enhancements and (2) low-profit customers who will settle for a product that is just “good enough”� if they can get it for a low price)

And if you talk to people at a company or look at their website, it’s not hard to find the commonly held views in that organization. Here are phrases on the websites of a few companies near where I live:

• An engineering company that does failure analysis: 90 scientific and engineering disciplines, unparalleled technical expertise, multidisciplinary, rapid-response
• A law firm: full-service international powerhouse, ethic of hard work, innovative approach to law firm management, high-profile and groundbreaking deals, collaborative process
• Maker of wetsuits: it’s always summer on the inside (of a wetsuit), surfer territories expanded, put all six kids to work, thriving international company, dominating the world’s wetsuit market

These commonplaces represent beliefs, not facts. They are rules of thumb that make communication easier between people who share common experiences. They also foster group identity because people outside the group may not understand the commonplaces. If you and I are in the same group, we can speak in shorthand and strengthen the link between us while simultaneously keeping others outside.

If you want to persuade an audience, learn its commonplaces. Then show how the decision you want your audience to make is not only advantageous to them, but is also a small leap from what they already believe.

Now that you have the attention of the audience (they see that you have similar values to them, that you have practical wisdom in this subject, and that you have their interest in mind), it’s time to get down to the core of your persuasion and show them the logic of your argument.

Since the subject is business, you are persuading your audience to enter into an economic relationship with you. You are asking them to change their mind and to change their willingness to act. Your logic needs to show how the choice you want them to make is advantageous to them, how it delivers the biggest return on their investment of resources and requires the least amount of change in how they work.

We are not talking about formal logic here, the logic of philosophy and science where the participants are pursuing Truth. Why don’t we use formal logic? One reason is that in most cases we don’t have the evidence to prove our case in the way that a philosopher or scientist does. And partly because even if we could, the audience would not necessarily find that persuasive.

The logic of rhetoric is an informal logic. You make an assertion and follow it with a conclusion. You begin with a premise that the audience can agree with and link it to the choice you want them to make.

Women find men attractive who drive sporty automobiles. Buy this sports car and you’ll get the attention you want.

Companies that deploy internet-based order entry applications experience significant ROI. Get the cost savings and productivity improvements with our new application.

But where do you start your logical argument? What is the premise? It always starts with the audience and where they are: their attitudes, beliefs, and opinions. Then you can move the audience from where they are now to the conclusion you want them to draw, to the action you want them to take.

When your argument asks the audience to make a choice or to take an action, you must convince the audience that the choice is advantageous to them. The decision to act belongs to the audience, but the burden of proof is on you. To make your proof persuasive, start with something your audience believes or wants.