2. What Is Critical Thinking?
Think it twice: Don’t take things for granted so easily.
Always ask the why-question: Try to find out the reason
(the premises) why certain claim (the conclusion) can be
supported.
Examine and evaluate the relationship between the
reasons and the claim.
3. Paradoxes
Self-defeating paradox: The concept of “all powerful” God
Zeno’s paradox: An apparently unacceptable conclusion
derived by apparently acceptable reasoning from
apparently acceptable premises
Semantic paradox: The liar’s paradox
The lawyer’s paradox
Prisoner’s dilemma
Russell’s paradox (Barber’s paradox)
The lottery paradox
4. What is logic?
Logic is not an empirical science
Formal or informal science
Logic v.s.Psychology:
1. The Laws of Thinking
2. The Science of Reasoning
3. The Science of Argument
The study of the methods and principles used to
distinguish good (correct) from bad (incorrect) reasoning
or argument.
The way to the good reasoning (making good argument) and
critical thinking
5. What Is an Argument?
An argument is the fundamental structure of the
reasoning.
An argument consists of premises and conclusion.
An argument is used to provide reasons for
supporting some claim or proposal.
Logic aims to the study of the various forms of
argument.
The ultimate goal of logic is to evaluate arguments.
6. The Standard Form of Argument
P = premise, C = conclusion
There must be some kind of supporting relationship between
premises and conclusion.
P1
P2
、
、
Pn (n≧1)
C
7. Two Kinds of Argument
The traditional but mistaken distinction between deduction
and induction:
Deduction Induction
Some general principles Some particular cases
↓ ↓
A particular case A general principle
10. Evaluating An Argument
There are two ways of evaluating an argument.
Formal logic is to use the deductive criterion for
evaluating arguments.
Informal logic is to use the inductive criterion
for evaluating argument.
11. The Criterion for Evaluating a
Deductive Argument
Deductive Argument
Valid Arg. Invalid Arg.
Sound Arg. Unsound Arg. Unsound Arg.
Good Arg. Bad Arg Bad Arg.
12. The Criterion for Evaluating an
Inductive Argument
Inductive Argument
Strong Arg. Weak Arg.
Cogent Arg. Uncogent Arg. Uncogent Arg.
Good Arg. Bad Arg. Bad Arg.
13. What Is a Good Argument
Deductive
Valid Invalid
Sound Unsound Unsound
Good Bad Bad
Inductive
Strong Weak
Cogent Uncogent Uncogent
Good Bad Bad
14. The Deductive Systems
The truth table methods for evaluating deductive
arguments
The formal system of natural deduction:
1. Propositional logic
2. Predicate logic
The Aristotelian logic (Categorical Syllogism)
The axiomatic system
15. The Inductive Systems
The methods of analogy and the probable inference
Legal reasoning
Mill’s method and causality
Statistical reasoning and probability
Hypothetical reasoning
16. Informal Fallacies
A fallacy is an error in reasoning.
Fallacies of relevance: When an argument relies upon
premises that are not relevant to its conclusion, and
therefore cannot possibly establish its truth
Fallacies of weak induction: When the connection between
premises and conclusion is not strong enough to support
the reasoning
Fallacies of presumption, ambiguity, and grammatical
analogy
17. The Uses of Logic
Evaluate someone else’s argument by exposing its
structure
Set up your own argument
Solve problems and puzzles by answering the why-
questions (giving the reasons)
Inference to the best through using the present evidences
Thinking effectively and making decision wisely
18. Logic and Critical Thinking
Why should we become a critical thinker?
Be the master of your own life
To ask “why?” is to ask for the reasons for some beliefs
and opinions (that is, to find out the premises for a certain
conclusion)
To evaluate how the reasons successfully support the
claim (that is, to evaluate how the premises support the
conclusion )
A critical thinker is a truth-pursuer, and logic is truth-
preserving.
