Contents analysis of theme Categories Examples Conclusion Analysis of theme

Formal Versus Informal Logic
1816-Yusupov Muhammadsodiq
CONTENTS
Analysis of theme
Categories
Examples
Conclusion
Analysis of theme
Two basic categories of human reasoning
Deduction: reasoning from general premises, which are known or presumed to be known, to more specific, certain conclusions.
Induction: reasoning from specific cases to more general, but uncertain, conclusions.
Both deductive and inductive arguments occur frequently and naturally…both forms of reasoning can be equally compelling and persuasive, and neither form is preferred over the other (Hollihan & Baske, 1994).
Deduction Vs. Induction
Deduction:

• commonly associated with “formal logic.”
• involves reasoning from known premises, or premises presumed to be true, to a certain conclusion.
• the conclusions reached are certain, inevitable, inescapable.

Induction

• commonly known as “informal logic,” or “everyday argument”
• involves drawing uncertain inferences, based on probabalistic reasoning.
• the conclusions reached are probable, reasonable, plausible, believable.

Deductive Versus Inductive Reasoning
Deduction

• It is the form or structure of a deductive argument that determines its validity
• the fundamental property of a valid, deductive argument is that if the premises are true, then the conclusion necessarily follows.
• The conclusion is said to be “entailed” in, or contained in, the premises.
• example: use of DNA testing to establish paternity

Induction

• By contrast, the form or structure of an inductive argument has little to do with its perceived believability or credibility, apart from making the argument seem more clear or more well-organized.
• The receiver (or a 3rd party) determines the worth of an inductive argument

Sample Deductive and
Inductive Arguments
Example of Deduction

• major premise: All tortoises are vegetarians
• minor premise: Bessie is a tortoise
• conclusion: Therefore, Bessie is a vegetarian

Example of Induction

• Boss to employee: “Biff has a tattoo of an anchor on his arm. He probably served in the Navy.”

Categories
Deduction Versus Induction ---continued

• Deductive reasoning is either “valid” or “invalid.” A deductive argument can’t be “sort of” valid.
• 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

• 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.

Deduction Versus Induction --still more

• Deductive reasoning is commonly found in the natural sciences or “hard” sciences, less so in everyday arguments
• Occasionally, everyday arguments do involve deductive reasoning:

Example: “Two or more persons are required to drive in the diamond lane. You don’t have two or more persons. Therefore you may not drive in the diamond lane”

• 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

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