(This section briefly discusses the main principles of logical reasoning.  Please consult a standard introductory logic text for many more details and qualifications. Introduction to Logic by Irving Copi and Carl Cohen and A Concise Introduction to Logic by Patrick Hurley are among the best. Both texts have been thoroughly consulted and used in the preparation of what appears here and in the sections that follow below. The American Heritage Dictionary has been consulted for basic definitions.)

Critical thinking helps us distinguish between knowledge and mere belief (or opinion or fantasy). Knowledge claims must be supported by evidence, and the evidence must exist in the proper relationship to the knowledge claim. This relationship is called an inference, and the study of these inferences is called logic. Logic generally speaking is the science of correct thinking or, more specifically, the study of what makes inferences correct or incorrect. Logic deals with the movement or inference from one or more statements to other statements according to rules, and it is these rules determine how certain statements support those that follow from them, as we shall see below.

Knowledge is belief supported by evidence and it is connected to this evidence by rules of inference.

Philosophers generally recognize two forms of human knowledge, perceptual and conceptual. Each has an immediate and mediated relationship between its knowledge claim and its evidence.

The major components of principles of logical reasoning are:

Perceptual Knowledge and Inference

Reliability of Inductive Generalizations

Argument by Analogy

Reliability of Analogical Arguments

Some Misuses of Inductive Generalizations

General Objections to Perceptual Knowledge

Objections Answered

Scientific Theory

Inductive Statistical Argument

Criteria for Evaluating Theories

Conceptual Knowledge and Inference

Immediate Inference

Square of Opposition

Mediated Inference

Categorical Syllogism

Disjunctive Syllogism

Hypothetical or Conditional Syllogism

Mixed Conditional

The Logic of Causality

Causal Connections

Causal Connections and Generality

Probability

General Definition

Classical Theory

Relative Frequency

Statistical Reasoning

The Statistical Mean