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

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
An Introduction To Reasoning is a critical reasoning and (introductory) logic text book which ...

• 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 2 sets of exercises after every section or every few sections, with answers to the even-numbered problems of exercise set 1

• for instructors: additional answers and supplementary exercises — 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

Real-World Reasoning

(Classifying, Analyzing, And Basic Evaluation)

Classifying & Analyzing

Spotting Reasons & Target

Reasoning vs. Non-
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

Everyday Inferences – Sources, Character, Motives

Everyday Inferences – Emotional Reasons

Everyday Inferences – Practical Reasoning

Everyday Inferences – Syntax, Basic Logic

Evaluation Using Warrants

​ ​
​ ​
– Basic
Diagramming Reasoning
​ ​
– Complex Reasoning
Diagramming Reasoning
​ ​
– Dialogue
Diagramming Reasoning
​ ​
– Extended Dialogue
Diagramming Reasoning
​ ​
– Very Long Passages

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

Venn Diagram Method (Categorical Logic)

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)

Notes & Bibliography

Real-World Reasoning (RW)
Classifying & Analyzing Reasoning (propositions; justifying belief and explaining; inferring and arguing; flag words; 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 – 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 – Practical Reasoning (Single section on decision-making)
Everyday Inferences – Basic Logic (Identity/difference, part-whole, symmetricality, transitivity, category instantiation, affirming the antecedent, chain, elimination)
Evaluation Using 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)

Propositional & Categorical Reasoning (P&C)
Validity & Non-Validity (Note: there is a section on valid-strong-weak in P&C, and a section on these three and soundness in RW's Basic Evaluation)
Logical Structure Of Propositions (Negations, Conjunctions, Disjunctions, Conditionals)
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) 
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)