Deductive Versus Inductive Appeals to Reason Ms. O’ Shea Riverside High School English IV

DEDUCTION Formal Logic It orders ideas from the general assertion to specific reasons and support that culminate in a certain, inevitable conclusion. GENERAL TO SPECIFIC Deductive reasoning employs the syllogism which moves from a major statement/premise, through a minor premise, to a conclusion. The premises are presumed to be true. In a valid, deductive argument, if the premises are true, then the conclusion necessarily follows.

ARISTOTLE’S FAMOUS SYLLOGISM MAJOR PREMISE:All men are mortal. MINOR PREMISE:Socrates is a man. CONCLUSION: Therefore Socrates is mortal. The conclusion is said to be “entailed” in, or contained in, the premises. The Law of the Sea treaty states that any vessel beyond a 12 mile limit is in international waters. The treaty also states that any vessel in international waters cannot be legally stopped or boarded. Therefore, when the U.S. Coast Guard intercepts boats coming from Cuba or Haiti more than 12 miles from the U.S. coast, it is violating the Law of the Sea.

Bessie tortoisesvegetarian animals sample “Venn diagram” of a deductive argument All tortoises fall in the circle of animals that are vegetarians Bessie falls into the circle of animals that are tortoises Thus, Bessie must be a vegetarian

DEDUCTION Deductive reasoning is either valid or invalid, that is completely correct or completely incorrect, nothing in between. This type of reasoning does not yield new knowledge; it clarifies concepts we know something about, and it is based on the truth of its premises. If the reasoning employed in an argument is valid and the argument’s premises are true, then the argument is said to be sound. valid reasoning + true premises = sound argument

More Deductive Arguments Suppose the following statements are all true: –Person L is shorter than person X –Person Y is shorter than person L –Person M is shorter than person Y What additional piece of information would be required to conclude that “Person Y is shorter than Person J”? A.Person L is taller than J B.Person X is taller than J C.Person J is taller than L D.Person J is taller than M E.Person M is taller than Y Solution: Answer C M < Y < L < X So, if J is taller than L, Y must be shorter than J

More Deductive Arguments Suppose every place in the world that people live is represented by the blue space inside the rectangle. Suppose the long pink oval represents all the wooden houses in the world. And, suppose the green circle represents Canada. The most logical conclusion one can draw from the figure is: A.all wooden houses are found in Canada B.Everyone lives in a wooden house C.Some Canadians live in wooden houses D.No one lives in Canada

The Sophism If one of the premises in a syllogism is unsound, the conclusion will be invalid. This creates a SOPHISM. Example: All women are wise. Kate is a woman. Therefore, Kate is wise.

SOPHISM If faulty reasoning and not an invalid premise creates the sophism, then the result will be one of the fallacies you’ve studied. Which do you recognize here?

Enthymeme The enthymeme is a syllogism in which one of the premises is implied, rather than being directly stated. “Wasps are insects. Therefore wasps have six legs.” What premise is unstated?

INDUCTION commonly known as “informal logic,” or “everyday argument”. It is embodied in the scientific method. Induction moves from the SPECIFIC (examples) to the GENERAL (conclusions), thereby reversing the process of deduction. involves drawing inferences from experimentation,examples,observations, and experiences. the conclusions reached are probable, reasonable, plausible, and believable.

INDUCTION EXAMPLES  A sample of fifty motorists who were stopped by the CHP at a sobriety checkpoint on a Saturday at midnight revealed that one in four drivers were either uninsured, intoxicated, or both. Thus, if you get involved in an accident on the freeway there is a 25% chance the other motorist will be drunk or uninsured.  Boss to employee: “Biff has a tattoo of an anchor on his arm. He probably served in the Navy.”  Observation: Tonya is seen walking from her car to her home with a set of golf clubs. Observation: Tonya’s husband Jeff loves golf and tomorrow is his birthday. Conclusion (inference): Tonya has bought the set of golf clubs for Jeff.

INDUCTION Arguments based on experience, experiment or observation are best expressed inductively, while arguments based on laws, rules, or other widely accepted principles are best expressed deductively. Inductive reasoning helps us to infer probable and likely conclusions and to gain new knowledge by examining statistical patterns. It also helps us to identify cause and effect. The analogy is an example of this type of reasooning.

INDUCTIVE REASONING Inductive reasoning enjoys a wide range of probability; it can be plausible, possible, reasonable, credible, etc. the inferences drawn may be placed on a continuum ranging from cogent at one end to fallacious at the other. Cogent (believable)_____________Fallacious (false)

Deduction Versus Induction Deductive reasoning is commonly found in the natural sciences or “hard” sciences, less so in everyday arguments. Inductive reasoning is found in the courtroom, the boardroom, the classroom, and throughout the media Most, but not all everyday arguments are based on induction Examples: The “reasonable person” standard in civil law, and the “beyond a reasonable doubt” standard in criminal law

SOURCES Adapted from commfaculty.fullerton.edu/rgass/.../Ded uction%20Vs.%20Induction.ppt