Chapter 2. Critical Thinking and Logic

Critical thinking means analysing information carefully, questioning assumptions, evaluating evidence and reasoning to a justified conclusion [2][17].

Arguments. An argument consists of premises (reasons) that support a conclusion. A valid argument has a conclusion that follows from the premises; a sound argument is valid and has true premises [2].

Deductive and inductive reasoning. Deduction moves from general rules to specific cases, guaranteeing the conclusion if the premises are true. Induction moves from observations to general conclusions that are probable, not certain.

Common fallacies

Fallacy	Description	Example
Ad hominem	Attacking the person, not the argument	“You can’t trust her view; she’s young.”
Straw man	Misrepresenting a view to attack it	Exaggerating an opponent’s position
False dilemma	Presenting only two options	“Either we ban it or society collapses.”
Slippery slope	Claiming one step will inevitably lead to extremes	“If we allow X, soon everything goes.”
Appeal to authority	Treating an authority’s claim as proof	“A celebrity said it, so it’s true.”
Circular reasoning	Assuming what is to be proved	“It’s true because it says so.”
Hasty generalization	Drawing broad conclusions from few cases	“I met two rude tourists; all are rude.”

Cognitive biases. People use mental shortcuts that can mislead, such as confirmation bias (favouring information that agrees with existing beliefs), the availability heuristic (judging likelihood by how easily examples come to mind) and anchoring. Awareness helps us check our own thinking [17].

Evaluating claims. Ask: What is the evidence? Who is the source and what are their interests? Is there a plausible alternative explanation? Do other sources agree?

Review: Identify the fallacy: “Everyone I know likes this film, so it must be the best.” (Answer: hasty generalization, and an appeal to popularity.)