Evaluating Whether a Conclusion is Justified

Some LNAT questions do not ask you to strengthen or weaken an argument but rather to evaluate whether the conclusion is justified by the evidence presented. This requires a different skill: assessing the logical relationship between premises and conclusion, considering scope, certainty, and whether the conclusion goes beyond what the evidence supports. This lesson teaches you to make that assessment systematically.

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What Does "Justified" Mean?

A conclusion is justified if, and to the extent that, the evidence and reasoning presented in the argument provide adequate support for it. A conclusion can be:

Status	Description
Fully justified	The evidence strongly and directly supports the conclusion as stated, with no significant logical gaps
Partially justified	The evidence supports a version of the conclusion but the conclusion as stated goes further than the evidence warrants
Not justified	The evidence does not logically support the conclusion, or the logical gap is too wide

Key Principle: Most LNAT conclusions are partially justified — the evidence provides some support, but the conclusion overstates, undergeneralises, or makes a leap that the evidence does not fully warrant. The skill tested is your ability to identify where and how the conclusion exceeds the evidence.

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Three Dimensions of Justification

When evaluating whether a conclusion is justified, consider three dimensions:

1. Scope

Does the conclusion apply to the same scope as the evidence?

Evidence scope	Conclusion scope	Problem
"A study of London schools found..."	"Schools across the UK should..."	Conclusion applies nationwide; evidence is London-specific
"Research on teenagers shows..."	"People of all ages..."	Conclusion applies to all ages; evidence covers only teenagers
"Data from 2019 indicates..."	"This has always been the case"	Conclusion is timeless; evidence is from one year

2. Certainty

Does the conclusion express the same level of certainty as the evidence supports?

Evidence certainty	Conclusion certainty	Problem
"The study suggests a link between..."	"This proves that..."	Evidence suggests; conclusion claims proof
"Preliminary findings indicate..."	"It is now established that..."	Preliminary findings are treated as established fact
"The data is consistent with..."	"The data shows conclusively that..."	Consistency is weaker than conclusive demonstration

3. Logical connection

Does the conclusion follow from the premises, or is there a gap?

Premises	Conclusion	Gap
"Policy X reduces cost A"	"Policy X should be adopted"	Reducing one cost does not mean the policy is beneficial overall — it may increase other costs
"Treatment Y is more effective than Z"	"Treatment Y should be prescribed for all patients"	More effective on average does not mean better for every individual patient
"Country A has policy P and outcome O"	"Country B should adopt policy P to achieve O"	Countries differ in many ways; what works in A may not work in B

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Worked Example 1

"A comprehensive study tracked 10,000 participants over twenty years and found that those who exercised for at least thirty minutes daily had a 40% lower risk of cardiovascular disease compared to sedentary individuals. Exercise therefore prevents cardiovascular disease."

Evaluating the conclusion

Dimension	Assessment
Scope	The study covered 10,000 people over twenty years — a substantial sample and duration. The scope is reasonable.
Certainty	The evidence shows a lower risk, not prevention. "Prevents" implies elimination of risk; "reduces risk by 40%" is what the evidence supports.
Logical connection	The study is observational (tracking participants), not experimental (assigning them to exercise). Active people may differ from sedentary people in other health-relevant ways (diet, genetics, socioeconomic status). The causal claim ("prevents") is stronger than the correlational evidence warrants.

A more justified conclusion would be: "Regular exercise is associated with a substantially lower risk of cardiovascular disease."

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Worked Example 2

"Exam results at Thornfield Academy improved by 12% in the year after the school introduced a new maths curriculum. The new curriculum is clearly more effective than the one it replaced."

Evaluating the conclusion

Dimension	Assessment
Scope	One school, one year. Too narrow to generalise.
Certainty	"Clearly more effective" expresses high certainty. A 12% improvement in one year at one school does not warrant this.
Logical connection	Many factors could explain the improvement: a stronger cohort of students, improved teaching (not just curriculum), increased motivation due to the novelty of a new programme, or simply regression to the mean if the previous year was unusually poor.

A more justified conclusion would be: "The results at Thornfield are encouraging and warrant further investigation across multiple schools and years."

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Common Patterns of Unjustified Conclusions

1. Correlation treated as causation

The evidence shows X and Y occur together; the conclusion claims X causes Y.

2. Part treated as whole

The evidence concerns a specific group, context, or time period; the conclusion generalises beyond it.