Course in Logic 101

From Logic

Welcome to Logic 101

Course Introduction

Everyone has an opinion, and in a democratic country everyone also has an equal right to state an opinion, but not everyone's opinion is of equal value. This page exists to spread this truth - some opinions are worth more than others*. And if you want your opinion to be the rational opinion, you must learn how to argue your points using the tenets of Logic.

  • Douglas Adams called this “opinion inequality”

Course Outline

The course in Logic 101 now proceeds to the opening page on Logic. Students ought to begin by reviewing this page.

Here is how the course proceeds. Students may also take note that proceeding in this fashion will also allow them to have a basic grasp of the history of logic.

The Laws of Classical Logic

This section presents the axioms of Classical Logic. Common myths about these axioms are also explored. Students will come to learn that these axioms only apply to certain logics.

The Difference Between Believing and Knowing

The two concepts are explained and differentiated.

Hans Eysenck's Rules of Argument

It's one thing to know how to argue, its quite another to know when to argue, and when to remain silent.

What is an Argument?

This section defines the term argument

Deductive and Inductive Logic

What is deduction? What is Induction? What are their limits?

Validity, Strength, Soundness and Cogency

In this section, the various ways to assess Deductive and Inductive arguments is explored.

Formal and Informal Logic

This section briefly explores the two main ways in which an argument can go wrong - i.e. problems with the form of an argument, and problems with the premises in an argument.

Informal Fallacies

This is both the longest section of the site, and most likely the most interesting. It presents a nearly exhaustive list of the most common informal fallacies.

Categorical Propositions

In order to learn Classical Logic one must first learn about the premises used in Classical arguments: Categorical Propositions.

Traditional Square of Opposition

The traditional Square of Opposition is a diagram specifying logical relations among the four types of categorical propositions described in the preceding section.

Modern Square of Opposition

It was eventually discovered that the Traditional Square of Opposition required a correction. This is it.

Classical Logic

Categorical Syllogisms are explained. One a student makes it to this point, they can claim to grasp the basics of Classical Logic.

Disjunctive and Hypothetical Syllogisms

However, there are other types of syllogisms. These are explored in this section.

Propositional Logic

Students will come to learn about the limits of Classical Logic. Propositional Logic represents one attempt to overcome these obstacles. Propositional Logic deals with using symbols to represent logical arguments.

Truth Tables

Truth tables provide a useful method of assessing the validity or invalidity of the form any argument. Once a student grasps Propositional Logic, they can begin to use Truth Tables.

Formal Fallacies A review of the valid and invalid forms of Propositional Logic.

Predicate Logic

Students will then come to see the limits of Propositional logic! Predicate logic helps overcome the shortcomings of both Propositional Logic and the problems found in the Traditional Square of Opposition.

Inductive Logic

There is more to logic than trading in tautologies. Inductive logic allows us to make statements about the real world. Included is a discussion of a possible basis of inductive logic: Bayesian Theory.


This section explores the nature of emotional appeals, and illustrates how they differ from logical arguments.

Resources for Further Learning

Conclusion and Adieu

For future consideration:

Common argument forms

Reductio ad Absurdum

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