Critical thinking – Systematic evaluation or formulation of beliefs/statements by rational
• It’s systematic because it involves distinct procedures and technical methods
(not just gut feelings).
• It’s used to evaluate existing beliefs and to formulate new ones.
• It evaluates beliefs in terms of how well they are supported by reasons
Statement (claim) – An assertion that something is or is not the case.
Premise A premise is a statement offered in support of a conclusion.
Conclusion – A conclusion is a statement that is held to be supported by a premise or
Argument – An argument is a set of statements one of which (the conclusion) is taken to be
supported by the remaining statements (the premises). AKA: The resulting
combination of premises and a conclusion
Inference – An inference is process of reasoning from a premise or premises to a conclusion,
based on those premises.
Two Crucial Points about Indicators:
(1) They may not actually be present in arguments.
(2) In arguments, premises do not always come before conclusions; conclusions do
not always come after premises
“Textual priority versus logical priority.”
Evaluating the truth-value of premises and conclusions is distinct from evaluating the logical strength of
arguments. TRUE/FALSE VALID/INVALID
Deductive Arguments –A deductive argument intends to provide logically conclusive support for the
Deductive Validity – An argument is deductively valid if and only if it is not possible for the premises
to be true and the conclusion false.
Valid argument Conclusion is logical based on given premise(s), REGARDLESS of trueness of premises.
Soundness – An argument is sound if and only if it is (a) deductively valid and (b) all its
premises are, in fact, true.
Inductive Strength – An argument is inductively strong if and only if the conclusion is probably true,
and Weakness given the premises. An argument is inductively weak if and only if it is not
Cogency – An inductive argument is cogent if and only if it is (a) inductively strong and (b)
all its premises are, in fact, true. Impediments to critical thinking:
Category 1 impediments (stem from how we think):
Self-interested – Accepting a claim solely on the grounds that it advances, or coincides with,
thinking our interests.
Group thinking – Peer pressure – Fallacy: an argument form that is both common and defective.
• Fallacy of appeal to popularity
• Fallacy of appeal to common practice
• Fallacy of appeal to tradition
• Genetic fallacy
Stereotyping: drawing conclusions about people or groups without sufficient
Three key ingredients in propositional knowledge:
• Justification Realism – there are objective truths in that subject area and what these truths are does not
depend upon anyone’s beliefs about them.
Category 2 impediments (stem from what we think):
Nihilism – There just are no truths whatsoever in that subject area.
Moral nihilism: The view that moral assertions have no truth-value (are neither true nor
Relativism – Subjective: what the truths are depends upon individuals
Social: what the truths are depends upon what a (majority) society or culture believes.
Skepticism – Statements have truth-values, but we don’t know what most or all of them are.
Pulling it All Together
(1) Each of the Category 2 impediments to critical thinking denies
something about truth or knowledge (or both):
(b) Relativism – subjective or social
(2) All three views appear to be self-defeating if taken to be about everything.
(3) In this course, we will take for granted that:
– assertions/statements in many subject areas have truth-values,
– these are objective, not relative to individuals or societies
– in principle, these can be known.
In other words, we’ll assume that realism about truth is, at the very least, the best default position in
A conditional statement is a statement of the form
If p, then q.
• If it rains, then the picnic will be cancelled.
• If Jones didn’t commit the murder, the butler did.
Conditionals are compound statements composed of two parts:
The antecedent – what follows the word “if”
The consequent – what follows the word “then”
A disjunctive statement is a statement of the form
Either p or q.
• Either the picnic was cancelled or it rained.
• Either Jones committed the murder or the butler did.
Disjunctions are compound statements composed of two parts called the disjuncts. Some valid conditional argument patterns:
1. Affirming the 2. Denying the consequent 3. Hypothetical Syllogism:
antecedent (Modus (Modus Tollens): If p, then q.
Ponens): If p, then q. If q, then r.
If p, then q. Not q. Therefore, if p, then r.
p. Therefore, not p.
Some invalid conditional argument patterns:
1. Denying the Antecedent: 2. Affirming the Consequent:
If p, then q. If p, then q.
Not p. q.
Therefore, not q. Therefore, p.
A valid disjunctive argument pattern:
(i) Either p or q. (ii) Either p or q.
Not p. Not q.
Therefore, q. Therefore, p.
Justification - In general, to be justified, beliefs (or statements, or premises) have to be based on
enough of the right kind of evidence. What kind is appropriate, and how much is
enough, depends on the context.
- a good rule of thumb: the higher the stakes, the more evidence is required for a belief
to be justified.
- in general, the more evidence we have for a claim, the more firmly we should believe
it: “We should proportion our belief to the evidence.”(p.127).
Some Ways a Claim Can be Justified:
1. It is true by definition. e.g. “All bachelors are unmarried adult males”
2. It is