Critical Reasoning

Critical Reasoning

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

Critical reasoning is the controlled evaluation of an argument — separating the conclusion (the claim being defended) from the premises (the reasons offered), and judging whether the evidence actually warrants the claim.

Three core moves carry almost every MDCAT item:

1. Locate the main conclusion. It is usually the most general, defensible statement — not the loudest or most emotional line.
2. Stress-test the link. Ask: if the premises are granted, must the conclusion follow? (deductive validity), or is the conclusion merely probable? (inductive strength).
3. Surface hidden assumptions. Find the unstated belief that bridges premises to conclusion; weaken or negate it to attack the argument.

A sound argument is a valid argument with true premises. A strong inductive argument has true, relevant premises that make the conclusion likely. Counterexamples, missing assumptions, and classic fallacies (ad hominem, straw man, false cause, hasty generalization) are the usual ways MDCAT breaks an argument.

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🟡 Standard — Regular Study (2d–2mo)

Standard content for students with a few days to months.

Anatomy of an Argument

Every argument has two structural pieces: premises (reasons/evidence) and a conclusion (what the reasons support). MDCAT often disguises the conclusion inside a long passage. Locate it by asking, Which sentence is the author trying to get me to accept? The conclusion is typically broader, more general, or appears in the final sentence of a paragraph.

Validity vs. Soundness vs. Strength

• Deductive validity: the conclusion must follow from the premises by form alone. Example form: All A are B. x is A. ∴ x is B. — valid regardless of subject matter.
• Soundness: a valid argument whose premises are actually true. Sound ⇒ conclusion is certainly true.
• Inductive strength: premises make the conclusion probable but not certain. Most real-world reasoning (scientific, statistical, analogical) is inductive.

A strong inductive argument can still be defeated by a single credible counterexample or a plausible alternative explanation.

Necessary vs. Sufficient Conditions

• A sufficient condition (S) guarantees the result: If S, then R.
• A necessary condition (N) must be present for the result, but on its own doesn’t produce it: If R, then N.

Confusing these (treating a necessary condition as sufficient) is a classic MDCAT trap.

Common Reasoning Patterns to Recognise

Pattern	What it does	Weakness to look for
Analogy	Argues two similar cases share a further property	Dissimilarity between the cases
Causal claim	Asserts A causes B	Confusing correlation with causation; missing mechanism
Generalisation	From a sample to a whole population	Biased or too-small sample
Appeal to authority	Relies on an expert’s word	Authority outside their domain, or no consensus
Conditional	Uses if–then logic	Denying the antecedent; affirming the consequent

Standard MDCAT Question Types

• Which of the following, if true, would most strengthen/weaken the argument?
• Which of the following is an assumption the argument requires?
• Which of the following is the main conclusion?
• Which statement must be false / could be true / is most analogous?

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🔴 Extended — Deep Study (3mo+)

Comprehensive coverage for students on a longer study timeline.

Fallacies You Must Name on Sight

• Ad hominem: attacks the person, not the claim.
• Straw man: distorts the opponent’s view into an easier-to-refute caricature.
• False cause (post hoc): assumes that because B follows A, A caused B — ignores coincidence, reverse causation, common cause.
• Hasty generalisation: leap from a small or atypical sample to a universal rule.
• Slippery slope: claims one step inevitably triggers a chain of extremes, without justifying each link.
• Circular reasoning: the conclusion is smuggled into the premises.
• Equivocation: a key word shifts meaning mid-argument.
• Red herring: introduces an irrelevant, emotionally charged topic to divert attention.
• Appeal to ignorance: treating absence of evidence for a claim as evidence against it (or vice versa).

Edge Cases That Trip Students

1. Strength ≠ truth. A strong inductive argument may still have a false conclusion; a weak one may coincidentally hit truth. Judge the link, not the answer’s factuality.
2. Persuasion is not validity. A fluent, credentialed author can still rely on a fallacy — never equate rhetorical force with logical force.
3. Negating the antecedent (If P then Q. Not P. ∴ Not Q.) and affirming the consequent (If P then Q. Q. ∴ P.) are both formally invalid but look natural in prose.
4. Necessary vs. sufficient trap: statements of the form “to pass, one must study” describe a necessary condition — studying is required but not enough.

Worked Mini-Example

Passage: “Students who use spaced repetition score higher on MDCAT than those who re-read notes. Therefore, spaced repetition is the cause of higher scores.”

• Conclusion: spaced repetition causes higher scores.
• Hidden assumption: the only systematic difference between the groups is the study method (no prior GPA, motivation, or coaching differences).
• Weaken by: showing the spaced-repetition group also had higher biology GPA.
• Fallacy risk: false cause — correlation presented as causation without controlling for confounders.

Practice Prompts

1. A news article argues that because city X installed new CCTV cameras and crime fell, the cameras caused the drop. Identify two hidden assumptions and one specific piece of evidence that would weaken the argument.
2. “If a vaccine is safe, no one will get side effects. Some people got side effects, so the vaccine is unsafe.” Name the logical form being misused, rewrite the argument so the structure is valid, and state what would actually be required to conclude the vaccine is unsafe.

MDCAT Weightage Tip

Logical Reasoning carries about 4% of the MDCAT paper — typically 2–3 critical-reasoning items. Each gives 60–90 seconds; spend them (i) finding the conclusion, (ii) stating the gap, (iii) choosing the option that attacks or supports that exact gap.

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