Logic Handouts: Basic Concepts and Reasoning

Fundamentals of Logic and ArgumentsPage 1

Logic is defined as the study of correct reasoning patterns. Central to logic are arguments, which consist of premises (supporting evidence) and a conclusion (the supported claim). Understanding logic is considered practical for living a better life, as it helps align our beliefs with the truth, which in turn leads to more effective actions.

Inductive vs. Deductive ArgumentsPage 1

Arguments are split into two types. Inductive arguments aim to show that a conclusion is probably true; they are evaluated based on strength and cogency (an argument is cogent if it is strong and has true premises). Deductive arguments aim to show that a conclusion must be true based on logical necessity; they are evaluated based on validity (if premises were true, the conclusion must be true) and soundness (a valid argument with true premises).

Evaluating Arguments and Common PitfallsPage 2

A valid deductive argument does not guarantee the truth of a conclusion unless it is also sound. Common logical mistakes include confusing validity with truth, failing to account for false premises, and confusing inductive strength with deductive certainty. A validity test asks: 'If the premises were true, would they guarantee the conclusion?'

Valid and Invalid Argument FormsPage 4

Common valid argument forms include Modus Ponens, Modus Tollens, Hypothetical Syllogism, Disjunctive Syllogism, and Constructive/Destructive Dilemmas. These have 'invalid look-alikes' such as Affirming the Consequent, Denying the Antecedent, and Affirming a Disjunct, which are frequent errors in reasoning.

Justification and Basic Sources of BeliefPage 6

Rational belief is not only supported by arguments but also by five basic sources: perception, memory, introspection, rational insight, and testimony. These provide prima facie justification. Beliefs can be extended by chain-linking these foundational sources through sound or cogent inferences.