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A substantial proportion of LNAT Section A questions ask you to identify what would strengthen or weaken an argument presented in a passage. These questions test a precise skill: the ability to evaluate how additional information affects the logical relationship between premises and conclusion. This lesson establishes the foundational concepts you need before tackling the specific techniques covered in the rest of this course.
Every argument consists of premises (reasons/evidence) offered in support of a conclusion. The logical connection between them is rarely airtight — most arguments in LNAT passages are inductive, meaning the premises make the conclusion probable rather than certain.
This gap between premises and conclusion is where strengthening and weakening operate:
| Action | What it does | Effect on the argument |
|---|---|---|
| Strengthening | Provides additional evidence or reasoning that makes the conclusion more likely to be true given the premises | The gap between premises and conclusion becomes smaller |
| Weakening | Provides additional evidence or reasoning that makes the conclusion less likely to be true given the premises | The gap between premises and conclusion becomes larger |
Key Principle: Strengthening and weakening are about probability, not proof. A strengthener does not prove the conclusion true, and a weakener does not prove it false. They shift the balance of evidence.
Think of an argument as a bridge between premises and conclusion. The premises are the supports, and the conclusion is the destination.
Most LNAT questions ask which option most strengthens or weakens — a matter of degree, not absolute proof.
Several common misconceptions about strengthening lead to incorrect answers:
| Misconception | Why it is wrong |
|---|---|
| "Repeating the conclusion in different words strengthens it" | Restating a claim adds no new evidence — it is circular |
| "Providing any evidence related to the topic strengthens the argument" | The evidence must specifically support the conclusion, not just be relevant to the topic |
| "Showing that the conclusion is popular strengthens it" | Popularity does not determine truth (appeal to popularity) |
| "Proving one premise true strengthens the argument" | If the argument has other flaws (e.g., a logical gap between premises and conclusion), confirming one premise may not help |
Similarly, common misconceptions about weakening include:
| Misconception | Why it is wrong |
|---|---|
| "Disagreeing with the conclusion weakens the argument" | Disagreement is not evidence — it is just an opposing assertion |
| "Showing that the author has a bias weakens the argument" | Bias is relevant to credibility but does not address the logic of the argument (this is an ad hominem concern) |
| "Providing a different argument for a different conclusion weakens the original" | A separate argument does not engage with the original's premises or logic |
| "Showing the conclusion is false weakens the argument" | LNAT questions ask about the reasoning, not about whether the conclusion happens to be true or false in the real world |
Consider the following argument:
"Countries that invest heavily in early childhood education see better outcomes in secondary school performance, lower crime rates, and higher lifetime earnings. The UK currently spends less on early childhood education than most comparable OECD countries. Increasing investment in early childhood education would therefore improve educational outcomes, reduce crime, and boost earnings in the UK."
| Component | Content |
|---|---|
| Premise 1 | Countries investing heavily in early childhood education see better outcomes |
| Premise 2 | The UK spends less than comparable OECD countries |
| Conclusion | Increasing UK investment would improve outcomes |
The argument assumes that what works in other countries would also work in the UK, and that the correlation between spending and outcomes is causal.
"A pilot programme in which three UK local authorities significantly increased early years spending over five years showed measurable improvements in primary school readiness and a reduction in youth offending rates."
This strengthens the argument because it provides UK-specific evidence that increased spending leads to the predicted outcomes, directly addressing the gap between international data and a UK-specific conclusion.
"An analysis of OECD data found that the countries with the best educational outcomes achieve them through teacher quality and curriculum design rather than overall spending levels, and that increases in spending alone do not predict improved results."
This weakens the argument because it suggests that spending levels are not the key variable — other factors drive the outcomes. If spending alone does not predict results, the argument's recommendation to increase spending is undermined.
When evaluating answer options, think of strengthening and weakening as a spectrum:
| Impact level | Description |
|---|---|
| Strongly strengthens | Directly provides evidence for the key assumption or fills the main logical gap |
| Somewhat strengthens | Provides supporting evidence that is partially relevant |
| Neutral | Has no bearing on the argument's logic |
| Somewhat weakens | Raises a concern that is partially relevant |
| Strongly weakens | Directly undermines the key assumption or shows a critical flaw |
LNAT Tip: "Most strengthens" and "most weakens" questions ask you to compare options and choose the one with the greatest logical impact. An option might be somewhat relevant but still be a weaker choice than one that strikes at the heart of the argument.
The most effective way to find strengtheners and weakeners is to identify what the argument needs to be true — its key assumptions and logical gaps.
"Student satisfaction surveys show that students at universities with smaller class sizes report higher levels of engagement. Universities should therefore reduce class sizes to improve the quality of education."
Conclusion: Universities should reduce class sizes. Key gap: The argument assumes that self-reported engagement equates to educational quality, and that reducing class sizes would cause (not merely correlate with) improved engagement.
Strengthener: Evidence that smaller class sizes lead to measurably better learning outcomes (e.g., higher grades, deeper understanding) — not just self-reported satisfaction.
Weakener: Evidence that universities with smaller class sizes also tend to be more selective, better funded, and more prestigious — suggesting that the smaller classes are a symptom of institutional quality rather than its cause.
Strengthening an argument means providing evidence that makes the conclusion more likely given the premises. Weakening means providing evidence that makes it less likely. Both operate on the logical connection between premises and conclusion, not on the truth of the conclusion itself. The most effective strengtheners and weakeners target the argument's key assumptions and logical gaps. LNAT questions typically ask which option most strengthens or weakens, requiring you to compare the logical impact of different pieces of evidence.