Types of Reasoning, Validity, Fallacies & Biases in Critical Thinking

Deductive Reasoning

Starts with a general rule and applies it to a specific case.

Goal of Deductive Reasoning

To guarantee the conclusion — if the premises are true, the conclusion must be true.

Inductive Reasoning

Uses specific examples to form a general rule.

Goal of Inductive Reasoning

The conclusion is probable, not guaranteed.

Validity in Deductive Reasoning

Valid & sound (premises guarantee conclusion).

Invalidity in Deductive Reasoning

Invalid or false premises.

Strength in Inductive Reasoning

Strong (evidence makes conclusion very likely).

Weakness in Inductive Reasoning

Weak (evidence too small, biased, or random).

Subjective

Based on personal opinion or feelings.

Objective

Based on facts, measurable or observable.

Resisting Contradicting Evidence

Ignoring or denying evidence that goes against your belief.

Looking for Confirming Evidence (Confirmation Bias)

Only paying attention to information that supports what you already believe.

Preferring Available Evidence (Availability Bias)

Relying on what comes easily to mind instead of actual statistics.

Motivated Reasoning

Letting your desires or emotions shape what you believe is true.

Illusion of Truth Effect

Repeating something makes it seem true — even if it isn't.

False Consensus Effect

Assuming most people agree with you when they don't. "Everyone loves pineapple on pizza!" (Actually, many don't.)

Dunning-Kruger Effect

People with low ability think they're more skilled than they are. Someone who's never studied medicine gives confident health advice online.

Strawman Fallacy

Misrepresenting someone's argument to make it easier to attack. A: "We should have stricter gun laws." B: "Oh, so you want to ban all guns?" (That's not what A said.)

Nut-Picking

Picking the most extreme example from the opposing side to make them look bad. Showing the craziest protester to "prove" everyone at the protest is unreasonable.

Whataboutism

Responding to criticism by pointing at someone else's wrongdoing. "You littered." "Well, what about you? You littered last week!"

Motivism

Saying someone's belief is wrong because of their motive, instead of their argument. "You only say that because you're jealous."

Pacifying (or Patronizing) the Opposition

Pretending to agree or "be nice" to avoid addressing real criticism. "I understand your feelings," but ignoring their actual points.

Ad Hoc Hypothesis

Making up excuses to protect your belief when it's disproven. "My psychic reading was wrong because the energy was off today."

Appeal to Common Practice

Saying something's okay because "everyone does it." "It's fine to cheat a little — everyone does it."

Appeal to Peer Pressure

Believing or doing something just to fit in. "Come on, everyone's skipping class; don't be lame."

Appeal to Tradition

Arguing something is right because it's "always been done that way." "We can't change this — it's how our family's done it for generations."

Face-Saving

Refusing to admit you're wrong to protect your ego or reputation. "I didn't mess up — the teacher just graded unfairly."

Subjectivist Fallacy

Claiming something is true "for me" but not for others, when it's an objective matter. "Gravity works for you, but I don't believe in it."

Confirmation Fallacy

Using only evidence that supports your claim while ignoring disconfirming evidence. "All my friends say my horoscope is accurate, so astrology is real."

Deductive

Definite (if premises true → conclusion must be true)

Inductive

In-progress (evidence suggests but doesn't guarantee)

Valid

Logic works

Sound

Logic works + premises true

Strong

Good inductive reasoning

Fallacy

Something that sounds logical but isn't