An Introduction To Reasoning is a set of three text-books, in critical reasoning, (introductory) logic, and scientific reasoning. It ...

• is free

• can be excerpted, e.g. if you want to teach/study truth tables but not truth trees

• can be modified as desired – the book is made available under a CC BY-NC-SA license

• includes a wide range of topics in critical reasoning and logic, including scientific reasoning. For details of coverage, see below.

• includes two sets of exercises after every section or every few sections, with answers to selected exercises of set 1

In brief, this means: you can change it, keep an attribution to Cathal Woods on it, don't sell it

Answers to additional problems and supplementary exercises for use in quizzes and exams are available to instructors by e-mailing cathalwoods at gmail

The book is made available for free under a Creative Commons BY-NC-SA license.

• for instructors: answer book and exercise sets 3 (and 4) — e-mail cathalwoods at gmail dot com for access

Get The Book (at Google Drive): An Introduction To Reasoning

If you have a Google account, (sign in and) add the material to your 'My Drive' for easier future reference – click 'Add to Drive' in the top right (then click 'Open in Drive' to go Drive). Note that it might take a few minutes for all of the files to show up in your Drive. If you see empty folders at first, wait patiently (or hit 'Reload' obsessively).

If you don't have a Google account, you can sign up here. If don't want one, you'll have to 'Open' and then 'Download as' (in the File menu) each file individually.

There is also a folder of other Free Reasoning Books.

Also available to instructors is a folder of supplementary exercises and answers – e-mail cathalwoods at gmail dot com for access.

Looking for predicate logic? Try P. D. Magnus's ForAllX, or Rob Loftis's remix ForAllX-Lorain County Remix

Brief Contents

Everyday Inferences – Sources, Character, Motives

Everyday Inferences – Emotional Reasons For Practical Conclusions

Everyday Inferences – Syntax, Basic Logic

Evaluation Using Warrants

Diagramming​ ​Reasoning​ ​– Basic

Diagramming Reasoning​ ​– Complex Reasoning

Diagramming Reasoning​ ​– Dialogue

Diagramming Reasoning​ ​– Extended Dialogue

Diagramming Reasoning​ ​– Very Long Passages

Real-World Reasoning

(Classifying, Analyzing, And Basic Evaluation)

Classifying & Analyzing

Spotting Reasons & Target

Reasoning vs. Non-​Reasoning

Justifying Belief vs. Explaining

Breaking Up Conjunctions

Rewriting Sentences​ As Propositions​

Putting Reasoning In Standard Form

Reasoning Substitutes

Problems With Meaning


Two Criteria Of Evaluation

Ignoring Confidence Indicators

Venn Diagram Method (Categorical Logic)

Propositional & Categorical Reasoning

(Valid inference)

Validity & Non-validity

Logically Structured Propositions

Necessary & Sufficient Conditions

Big 8 Method

Logical Symbols

Method Of Derivation/Proof

Truth Functions

Truth Table Method

Truth Tree Method


Inductive & Scientific Reasoning

(Inference from experience)

Valid, Strong, & Weak


Explanation-Building (including

INUS Conditions)

Experimental Methods



Inference To A Cause & To An Effect

Inference To The Best Explanation

Detailed Contents (with links to Parts and Chapters)

Preface & Notes


Notes & Bibliography

Real-World Reasoning (RW)


Classifying 1 (flag words; reasoning vs. non-reasoning)

Classifying 2 (justifying belief vs. explaining; inferring vs. arguing)

Analyzing 1 (propositions; conjunctions)

Analyzing 2 (standard form; rewriting sentences; things to omit)

Reasoning Substitutes (various ways not to reason, or to short-circuit reason-giving, by claiming the reasons are obvious, pointing imprecisely at reasons, shifting the burden of proof, appealing to ignorance, abusing flag words, begging the question)

Problems With Meaning – (imprecise language, euphemism, metaphor, vagueness, weasel words, ambiguity)

Two Criteria Of Evaluation – (soundness; valid-strong-weak; ignoring confidence indicators)

Everyday Inferences – Sources, Character, Motives (sources, character, motives: argument from authority; various ad hominems)

Everyday Inferences – Emotional Reasons For Practical Conclusions (Decision-making)

Everyday Inferences – Reasoning With Properties, Parts, & Relations (Identity/difference, part-whole, symmetricality, chain (with relations), transitivity)

Everyday Inferences – Reasoning With Classes & Propositions (chain (with classes), instantiation, affirming the antecedent, chain (with propositions), elimination)

Warrants – (Adding warrants/missing premises, sincerity & charity)

Diagramming - Basic (Standard form and diagramming of single-target reasoning)

Diagramming - Complex (Multiple targets, either from a single set of reasons or in sequence)

Diagramming - Dialogue(Objections, objections to objections, support for objections)

Diagramming - Very Long Passages

Propositional & Categorical Reasoning (P&C)

Validity & Non-Validity (Note: there is a section on valid-strong-weak (and soundness) in RW's Two Criteria)

Logical Structure Of Propositions (Negations, Conjunctions, Disjunctions, Conditionals)

Necessary & Sufficient Conditions

Big 8 Method (Single-step derivation using 8 basic rules)

Method Of Derivation (Multi-step derivation)

Truth Tables & Truth Trees

Categorical Reasoning (Very rudimentary introduction)

Inductive & Scientific Reasoning (I&S)

Valid, Strong, Weak (Note: there's a separate section on valid-not valid in P&C, and a quick section on valid-strong-weak and soundness in RW's Basic Evaluation.)

Causation, Causal Explanation & Causal Inferences (Causation & Causal Explanation, Inference to a Cause, Inference to an Effect)

Analogy & Inference To The Best Explanation (Hypothesis development when at a loss)

Experimental Methods (Controlled, Randomized, Prospective, Retrospective, Natural)

Mill's Methods

Induction (Generalization, Instantiation and Induction to a Particular)

Problems In Induction (Problem of Induction, New Riddle of Induction, Lottery Paradox. Philosophical appendix - No Exercises.)

Association Diagrams & Cross-Tabulations (Association, Cross-Tabulations, Present-Present Fallacy)

Explanation-Building (including INUS Conditions)