All formal reasoning can be divided into inductive and deductive techniques. In the simplest terms, inductive reasoning uses the facts available to propose to a larger conclusion. Deductive reasoning limits conclusions to the facts available and guarantees that the result is 100 percent true.
Inductive reasoning is often called "top-down" reasoning, starting with a larger observation and working "down" to explain specific facts. Deductive reasoning, by comparison, is called "bottom-up." Both inductive and deductive reasoning are vital to ordered thought, and there are advantages and disadvantages to both techniques in speech writing.
In the context of speech writing, inductive reasoning and deductive reasoning both have a place:
That said, if you're putting together a speech, you're almost certainly going to rely on inductive reasoning. This is simply because, if you've arrived at an incontrovertible deductive result, a speech shouldn't be necessary. Simply presenting your results will be enough.
Questions of history, politics, religion and the arts, on the other hand, often have no definitive "right answer." That's where well-ordered inductive reasoning comes in. Here follow several inductive techniques to use in your speech writing:
It is characteristic of inductive reasoning to start with observed facts. Then, you can go on to propose a possible explanation. By contrast, deductive reasoning starts with a theory, then goes through the process of observation to arrive at a conclusion.
Starting with an observation - "School absences seem to go up in the winter. Why?" - engages the audience by presenting them with a question that has no clear answer. In doing so, it gives you the opportunity to present your arguments and arrive at your inductive conclusion.
You still need to employ intellectual rigor when using inductive techniques! Since deductive reasoning has only one right answer while inductive reasoning has several, it can be tempting to see all inductive arguments as equally valid. That is not the case. Good inductive reasoning goes through all possible arguments, identifies all perceptible flaws, and arrives at the best available conclusion. Scientists call it being less wrong.
Take our observation about school absences. Why might absences go up in the winter? Do buses break down more often? The motor pool says no. Are people more inclined to stay home in cold weather? Based on teacher absences, yes, but not enough to explain the spike in student absences.
Walking your audience - briefly, you don't want to bore them! - through each major argument you explored and discarded is crucial in demonstrating the thoroughness of your inductive process.
A deductive conclusion is proven. Questions are, by definition, unnecessary. Inductive conclusions are subject to more analysis, since the object is less to be "right" than it is to be "as right as possible."
To return to our increased school absences, suppose we reach the conclusion that school absences go up in the winter because of increased illness in the student body. We have information to support that conclusion: the school nurse confirms a higher visitation rate and the secretary notes more parents are calling their students in ill.
That's an excellent conclusion, and it's the one we have presented.
Questions may address the premises on which the conclusion is based: "Parents may be calling students in ill for reasons other than actual illness."
They may also question the conclusion itself: "Just because illness is more common in the winter doesn't explain the increase in absences."
In either case, questions are a good thing. In preparing an inductive speech, you should ask yourself those questions and prepare defenses. That way, when the audience raises them, you've already got your answer in hand. Better yet, if you ask yourself a question your conclusion doesn't answer, you may come to an even stronger, better supported conclusion!
Most people explain the inductive technique by pointing out that it is when you begin a speech with a question that you want to answer. Instead of leading off with a thesis statement, a speaker will ask a question, such as, "Is it beneficial to have a flat tax rate in the United States?"
Then, the speaker answers the question in the speech by sharing all the possible positives and negatives that are associated with the question, such as, "It might be more equal if everyone is expected to pay the same amount, but we are sure that most people cannot afford a high tax rate, especially if unemployed."
By the end, the speech would point out all the arguments in favor of one answer and others that are not. The point is to outline all the possible reasons why you would choose yes or no, and then eventually lead to a logical conclusion based upon the information that is shared.
Some questions simply don't have clear, definitive answers. Many such questions are best addressed in the context of speech and debate. Speech and debate are systems of inductive reasoning used to find the best possible answer when determining the absolute truth isn't possible.