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The ultimate question in critical thinking is whether a conclusion is justified by the evidence and reasoning provided. On the LNAT, several question types test this directly: "Does the evidence support the author's conclusion?", "Is the author's conclusion justified?", or "Which of the following conclusions is best supported by the passage?" This lesson provides a framework for making this judgement systematically.
A conclusion is justified when the evidence and reasoning provided give sufficient grounds for accepting it. This does not mean the conclusion must be proven beyond all doubt — very few arguments in real life achieve certainty. It means the evidence makes the conclusion reasonable to accept.
A conclusion is unjustified when:
To evaluate whether a conclusion is justified, systematically examine the gap between what the evidence shows and what the conclusion claims.
| Step | Question | What to look for |
|---|---|---|
| 1 | What does the evidence actually show? | Strip away the author's interpretation and look at the raw evidence |
| 2 | What does the conclusion claim? | Identify the precise scope and strength of the conclusion |
| 3 | Is there a gap? | Does the conclusion go beyond the evidence in scope, certainty, or specificity? |
| 4 | How large is the gap? | A small gap may be acceptable; a large gap means the conclusion is unjustified |
The evidence supports a narrow claim, but the conclusion makes a broad one.
Evidence: "A study found that students in London schools who received additional maths tutoring improved their GCSE grades." Conclusion: "Additional tutoring improves academic performance."
Gap: The evidence is about maths tutoring for London students at GCSE level. The conclusion generalises to all tutoring, all students, and all academic performance.
The evidence suggests something is probable, but the conclusion states it as certain.
Evidence: "Research indicates a correlation between social media use and anxiety in teenagers." Conclusion: "Social media causes anxiety in teenagers."
Gap: A correlation has been inflated to a causal claim, and "indicates" has been upgraded to a definitive statement.
The evidence describes how things are, but the conclusion prescribes what should be done.
Evidence: "Air pollution levels in British cities exceed safe limits." Conclusion: "The government must ban all diesel vehicles from urban areas."
Gap: The evidence establishes a problem. The conclusion jumps to a specific, extreme solution. Many other solutions exist, and the evidence does not indicate that this particular one is the right approach.
The evidence shows what happened in the past, but the conclusion predicts the future.
Evidence: "House prices in the South East have risen by 8% annually for the past five years." Conclusion: "House prices in the South East will continue to rise."
Gap: Past trends do not guarantee future continuation. Economic conditions, interest rates, and other factors could change.
Passage:
"A nationwide survey of 15,000 adults found that 62% of respondents believed the criminal justice system is too lenient on violent offenders. When asked specifically about sentencing, 71% favoured longer prison terms for assault and robbery. The government should clearly respond to this strong public mandate by introducing mandatory minimum sentences for all violent crimes."
Evaluating the conclusion:
| Element | Assessment |
|---|---|
| Evidence quality | Moderately strong — a large, nationwide survey (15,000 respondents) |
| What the evidence shows | A majority of surveyed adults believe the system is too lenient and favour longer sentences for assault and robbery |
| What the conclusion claims | The government should introduce mandatory minimum sentences for ALL violent crimes |
Gaps identified:
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