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

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.