Building Your Argument for Persuasion:
Using Logic to Evaluate and Create Valid Arguments
Drawing Conclusions: Deduction vs. Induction | |
Logic: a science that deals with the principles and criteria of validity of inference and demonstration : the science of the formal principles of reasoning | |
Deduction and Induction are both common methods of using logic to make inferences & generalizations and draw conclusions based on the facts. Both occur naturally in the course of human interaction and can often be found to be interchangeable. Be open-minded but vigilant. | |
Deduction | -reasoning from general premises, which are known or
presumed to be known, to more specific, certain conclusions; uses
conditional (if, then) statements -used to draw conclusions -often called Formal Logic -EX. Everything that goes up must come down. And so, if you kick a ball up, it must come down. -Extremely powerful logic because, if the premise is true (usually by definition/scientific fact), then the conclusion is inescapable. Danger: Virtually none! Practice: Create an if, then statement from the example. Then, create five deductive arguments you might find in everyday life; express them as if, then statements. |
Induction | -reasoning from specific cases to more general, but
uncertain, conclusions -often used to draw inferences, generalizations -often called Informal Logic or Everyday Argument -EX. I've noticed previously that every time I kick a ball up, it comes back down, so I guess this next time when I kick it up, it will come back down, too. -As you can see from the example, induction often matches up with deduction. -Powerful in persuasion since it is often common sense. Danger: Because this type of reasoning relies on the probability of the next case and is based on a limited set of cases, it can break down. In debate, this can be attacked. -EX. All the boys I have dated have been insensitive and cold; therefore, all boys are insensitive and cold. Practice: List five common inductive arguments from everyday life and trade with a partner. Partners then analyze the arguments for validity. If valid, indicate so; if not, explain why not. |
Logical Relationships |
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Cause & Effect | -Very much related to a conditional statement (if A, then
B), this form of logical relationship is powerful. Essentially, it
shows how one action causes another. -Useful in persuading an audience of the good or bad consequences of a given act. Key Words: because, therefore, so, since Danger: The Cause & Effect Fallacy |
Comparison and Contrast | -Shows how two or more concepts are alike (comparison) or
different (contrast) -Useful in persuasion by granting similarities between positions and by illustrating differences between positions; also useful for helping you evaluate the relative strengths and weaknesses of your position. Good for prewriting. -Helpful Hint: Venn Diagrams are invaluable for these. Key Words (comparison): also, both, similarly Key Words (contrast): but, however, unlike Danger: Incomplete Analysis, Poor Analogies, Bias |
Analogy | -Shows a parallel relationship between something you are
trying to prove and a familiar, similar situation that supports your
position. -EX. Blaming America for the recent terrorist attacks against it is like blaming a rape victim for inviting her rape. -This example needs analysis - do you agree? Do the facts support this analogy? Are the concepts really similar? Are they of equal importance? Is the analogy just being used to hide a weak argument? -Useful in persuasion by relating your topic to those that may be more familiar and appealing to your audience. Key Words: like or as Danger: Inconsistencies in the comparison Practice: Do 1-5 bottom of p. 494 of Language Network. |