Unit 1: Introduction to Logic

The Science and Art of Correct Reasoning.

Table of Contents

1. Definition and Nature of Logic

Logic is derived from the Greek word 'Logos', which means both "thought" and "word" (the expression of thought in language).

Formal Definition: Logic is the study of the methods and principles used to distinguish correct from incorrect reasoning.

It is often called the "Science of Sciences" because it provides the rules of reasoning that all other sciences must follow. It is also an Art, as it teaches us how to apply these rules in our daily discourse.

2. Scope: Formal vs. Material Truth

Logic is primarily concerned with Formal Truth. It doesn't care if the facts are true in the real world; it only cares if the conclusion follows logically from the premises.

3. The Structure of an Argument

An argument is not a "disagreement." In logic, an Argument is a group of propositions where one (the conclusion) is claimed to follow from the others (the premises).

4. Deduction and Induction

Deductive Logic Inductive Logic
Moves from General to Particular. Moves from Particular to General.
Claims 100% certainty (Validity). Claims Probability.
If premises are true, conclusion must be true. Conclusion goes beyond what is in the premises.

5. The Fundamental Laws of Thought

Logic rests on three bedrock principles established by Aristotle:

  1. The Law of Identity: A thing is what it is (A = A).
  2. The Law of Non-Contradiction: A thing cannot be both A and not-A at the same time and in the same sense.
  3. The Law of Excluded Middle: A thing is either A or not-A; there is no third middle ground.

Exam Focus

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