Principles of Logic and Common Logical Fallacies

Fundamentals of Logic

Logic is a philosophical discipline that studies the correctness or validity of reasoning to discover the nature of arguments and false arguments.

Key Components of Reasoning

• Premises: A set of expressed data items.
• Conclusion: The final statement that expresses the new information obtained from the premises.

Types of Inference

Deduction: Consists of passing from general premises to a general conclusion. When this type of inference is correct, the conclusion follows necessarily from its premises: it is an impossibility for the premises to be true while the conclusion is false.

Induction: A type of reasoning that reaches a general conclusion from specific reports given in the premises.

Branches of Logic

Formal Logic: Focuses on whether reasoning is well-constructed by looking at the relations that the premises and the conclusion keep.

Informal Logic: It has to do with nothing formal; it determines the validity of reasoning by looking at aspects beyond its structure: whether or not the premises are adequate, if the data items can really justify the conclusion—that is to say, it takes into account non-formal issues.

Understanding Logical Fallacies

Fallacies: These are invalid reasonings; however, they can seem valid.

Categories of Fallacies

• Formal Fallacies: Formal logic studies these because they are the result of the failure to comply with a law of deduction.
• Informal Fallacies: Informal logic studies these because they involve questions related to the content, meaning, and the quantity of information. Reasoning is not always fallacious; it depends on the context.

Common Informal Fallacies

• Fallacy ad verecundiam: Defending the conclusion by appealing to somebody or something considered an authority without giving other reasons that justify it.
• Fallacy ad hominem: Seeking to rebut the reasoning of another or demonstrate the falsity of a conclusion by discrediting the person who defends it.
• Fallacies ad populum: Defending a conclusion without justifying it by appealing to sentiments.
• Fallacy ad ignorantiam: Defending that something is definitely true (or false) because we cannot demonstrate otherwise.
• Ad baculum fallacy: This happens when we threaten or coerce someone.
• Undue Generalization: Reaching a general conclusion from a few cases that are not enough to justify it, meaning it can be easily debunked with a counterexample.
• False cause: Providing an insufficient or incorrect cause.
• Fallacy semantics: Based on an expression that is repeated but changes its meaning in the course of the inference.
• Circular fallacy: The conclusion is supported by a premise that, to be true, depends on the conclusion itself.