Strengthen, Weaken and Flaw — CLAT Logical Reasoning
Strengthen, weaken and flaw questions all target the same soft spot: the gap between the premises and the conclusion. A strengthen answer makes the conclusion more likely; a weaken answer makes it less likely; a flaw answer names what is wrong with the jump. Master the handful of recurring reasoning errors and you will see the answer before you read the options.
1. It all comes down to the gap
Every argument has an assumption bridging its premises to its conclusion (the previous chapter). Strengthen and weaken questions work on that bridge:
- To weaken, find the option that makes the leap from premises to conclusion less safe — often by offering an alternative explanation or a counterexample.
- To strengthen, find the option that makes the leap more secure — often by ruling out an alternative or confirming the needed link.
The move that wins most weaken questions: supply another cause for the same evidence. If the argument says "X caused Y", an option showing Y could have been caused by Z weakens it.
2. Weaken — the toolkit
An option weakens an argument if it does any of these:
- Alternative cause — the effect could be due to something else. (Sales rose after the ad — but prices were also cut that week.)
- Counterexample — a case that breaks the generalisation. (All swans are white — here is a black one.)
- Attacks the assumption — shows the unstated link is false. (The survey assumed its sample was typical — it was not.)
- Reverses causation — Y may have caused X, not X caused Y.
- Unrepresentative evidence — the sample is too small, biased, or unusual.
Not a weakener: an option that merely restates the conclusion's opposite as an assertion, or raises an issue the argument never depended on. A weakener must engage the actual reasoning.
3. Strengthen — the toolkit
An option strengthens an argument if it:
- Rules out an alternative cause — the most powerful strengthener for causal arguments.
- Confirms the assumption — states directly that the needed link holds.
- Adds a supporting instance — another case that fits the conclusion.
- Removes a doubt — closes a loophole the argument left open.
Symmetry to remember: the best strengthen and weaken answers usually hit the same assumption from opposite sides. Find the assumption first, then decide the direction the stem asks for.
4. Flaw — naming the error
A flaw question asks you to describe what is wrong with the reasoning. The wrong answers describe errors the argument did not make. Learn the classic flaws by name:
| Flaw | What it is | Tell-tale |
|---|---|---|
| Post hoc (false cause) | Treats "after this" as "because of this" | X happened, then Y, so X caused Y |
| Correlation ≠ causation | Two things vary together, so one causes the other | Ignores a common third cause |
| Hasty generalisation | A big claim from too few cases | "I met two rude waiters, so this city is rude" |
| Ad hominem | Attacks the person, not the argument | "He's biased, so he's wrong" |
| Circular reasoning | The conclusion is assumed in a premise | "It's the best because nothing is better" |
| False dilemma | Only two options presented, when more exist | "Either ban it or accept chaos" |
| Equivocation | A word shifts meaning mid-argument | Uses "free" as no-cost, then as liberty |
| Appeal to authority/popularity | True because an authority/the crowd says so | "Millions buy it, so it works" |
| Straw man | Refutes a distorted version of the opponent's view | Exaggerates then knocks down |
5. The step-by-step method
- Pin the conclusion and the assumption that bridges it.
- Read the stem — strengthen, weaken, or flaw? (A reverser here is the most common careless loss.)
- Prephrase: for weaken, imagine the alternative cause; for strengthen, imagine ruling it out; for flaw, name the error.
- Scan for your prephrase among the options; the closest match is usually right.
- Test the top candidate: does it actually change how likely the conclusion is (strengthen/weaken), or does it accurately name the reasoning error (flaw)?
Degree matters: the question asks which option most strengthens or weakens. Several options may nudge the argument; choose the one with the biggest effect on the conclusion.
6. Common distractors
- Right direction, wrong argument — supports a claim the passage did not make.
- Real-world true, logically irrelevant — a true fact that does not touch the assumption.
- Too weak — nudges the conclusion slightly when a stronger option exists.
- Flaw that wasn't committed — names a textbook error the argument never actually made.
7. Exam protocol
- Locate the conclusion and its assumption before the options.
- Fix the direction from the stem; beware reversers.
- For weaken, hunt an alternative cause / counterexample; for strengthen, hunt a ruled-out alternative.
- For flaw, name the error first, then find the option that matches it.
- Prefer the option with the greatest effect — "most" strengthens/weakens.
- Discard options that are true but irrelevant to the argument's assumption.
