IELTS Vocabulary for Cause and Effect: Claim Only What the Evidence Supports

A Writing Task 2 prompt: "In many countries, people are moving from rural areas to cities. What are the causes of this trend, and what effects does it have?"

A common answer starts like this:

"This trend is caused by many reasons. The main reason is jobs. This causes many problems and it is proven that cities become overcrowded."

Every claim in that paragraph is too big or too vague. Many reasons names none. Caused by treats a slow, mixed process as a single switch. Proven claims certainty the writer does not have.

Cause-and-effect questions, in Writing Task 2 and in Speaking Part 3, test whether you can say how strong a link is. Not every cause causes directly. Not every effect is proven. The words in this guide let you match the claim to the evidence. That is what the Lexical Resource descriptors mean by using vocabulary "to convey precise meaning."

The lexical decision: how strong is the link?

Every cause-and-effect sentence makes three choices:

1. Is the cause direct, or does it create the conditions for something to grow?
2. Does the evidence confirm the effect, or only point toward it?
3. Did the solution actually work, and is that the same as working cheaply?

Each choice has a precise word and a set of near-words that get confused with it.

1. Foster vs. cause: direct effect or conditions for growth?

Foster means to create the conditions for something to develop over time. It does not mean to make something happen directly or right away.

"Cheap urban housing in the 1990s fostered a culture of internal migration that outlasted the housing itself."

Compare:

"The factory closure caused 2,000 job losses in a single month."

Caused is right for the closure: one event, one direct result. Fostered is right for the housing: a condition that let something develop gradually.

Two things about foster that IELTS candidates often get wrong:

• It is not always positive. Foster names the mechanism, not the direction. Subsidies fostered dependency and unplanned growth fostered informal settlements are both natural. Using foster only for good outcomes gives up one of its most useful moves: naming an unintended negative effect precisely.
• It needs a specific object. Fostered economic growth through low-interest loans reads as a real claim. Fostered development and progress reads as filler.

The near-words:

• Drive claims force and direct control: demand drove prices up. Use it when the cause pushes hard and fast.
• Encourage describes a moment, usually a person or policy acting on someone: the government encouraged families to move.
• Contribute to claims a partial role: one cause among several. It is the safest verb when you are not sure a cause was the main one.
• Facilitate removes friction from a process that was already happening: new rail links facilitated commuting.

Overclaiming with cause and drive is one of the most common precision errors in cause-and-effect essays. If the effect took years and had several sources, foster or contribute to is the accurate word.

2. Boil down to: naming the root cause

Once you have listed causes, examiners reward the writer who can say which one matters most. The spoken expression for that is boil down to: after the detail is stripped away, this is what is left.

"There are several factors, but it boils down to wages: people move to where the work pays."

Grammar to get right: boil down to X, where X is a noun or -ing form. Not boils to, not boils down into, and not boils down to that wages are higher.

Two register notes:

• Boil down to is neutral-to-casual. It is natural in Speaking Part 3 and acceptable in Task 2, but in a formal paragraph ultimately comes down to or is ultimately a matter of reads slightly more written.
• Boil down to names the essential cause. It does not mean reduce in the sense of cutting a quantity. "The government boiled down the budget" is not English.

The near-words: come down to is close to identical and slightly more formal. Hinge on and depend on describe a condition that decides an outcome, not the cause that explains it: whether the trend continues hinges on housing policy.

3. Bear out vs. suggest: how much does the evidence confirm?

The single most costly precision error in cause-and-effect writing is claiming proof. The word for evidence that confirms a claim is bear out.

"Census data bears out the link between wage gaps and migration."

Use it when the evidence does the confirming work. When it does not, use a weaker verb and keep the claim honest:

• Suggest — the evidence points toward the claim: survey results suggest a link.
• Support — the evidence is consistent with the claim without settling it.
• Bear out — the evidence confirms a claim that was previously uncertain.
• Prove — reserve this for cases where nothing is left in doubt. In an IELTS essay that is almost never.

Bear out takes a claim-like object: a hypothesis, a prediction, a concern, an assumption. The data bears out the government is wrong; the data bears out the government's forecast is right.

Candidates often forget the negative form. It is the polite way to disagree with a premise in the question:

"The assumption that migrants leave for lifestyle reasons is not borne out by the data; wages explain most of the movement."

Spelling: the passive is borne out, not born out.

4. Shed light on: explaining without claiming proof

Sometimes the evidence explains a cause without confirming it. That is what shed light on does: it contributes understanding to something that was unclear.

"Interviews with recent migrants shed light on why families leave even when city wages are only slightly higher."

The near-words test different claims:

• Explain claims the matter is settled. Shed light on claims progress, not closure.
• Highlight points at something already known. Shed light on needs a genuine puzzle.
• Expose or uncover imply concealment or wrongdoing. Shed light on is neutral.

Grammar: shed does not change form (shed, not shedded). The preposition is on. Light has no article: shed light on, or softened, shed some light on. Shed a light on is a common error. And shed jobs or shed costs is a different verb entirely, meaning to get rid of.

5. Efficacy vs. efficiency: did the solution work?

Problem-and-solution prompts ask you to judge a fix. The precise noun for did it produce the intended effect is efficacy.

"The efficacy of rural investment programs is mixed: they slow migration in the short term but rarely reverse it."

The word an advanced candidate must keep separate is efficiency, which is about how cheaply or quickly something works, not whether it works at all. The most useful sentence shape in this cluster puts the two side by side:

"Housing vouchers are efficient to administer but have shown little efficacy in reducing overcrowding."

A cheap, fast policy with no effect has high efficiency and zero efficacy. Candidates who only know effective cannot make that point.

Two more boundaries: efficacy is uncountable in ordinary use (not efficacies), and it describes interventions, not people. A person can be effective; a program has efficacy.

6. Pan out vs. play out: how the effect unfolded

Speaking Part 3 often asks how a change turned out. Two phrasal verbs cover this, and they make different claims.

• Play out describes how a situation unfolded, with no judgment about success: "We saw how the policy played out over a decade."
• Pan out judges the result against the hope attached to it: "The relocation scheme didn't pan out."

Pan out never takes an object. Pan out the plan is not English; the plan pans out or it doesn't. It is also business-casual: natural in Speaking, and better replaced in a formal essay by did not materialize or failed to deliver the expected results.

Turn out is the third neighbor, used for a surprising fact rather than an outcome: it turned out that most migrants were under 25.

Lower-scoring and higher-scoring: the same causes, different precision

Prompt: "Why are fewer young people learning practical trades, and what are the effects?"

Lower-scoring version:

"This is caused by universities. Everyone wants a degree and this causes a big lack of workers. It is proven that this is bad for the economy."

Higher-scoring version:

"The shift ultimately boils down to status: decades of policy fostered the idea that a degree is the only respectable route, even where trade wages are higher. Employment data bears out the effect on supply, with unfilled vacancies in construction and electrical work in most developed economies. What the data does not yet show is the long-term cost; recent studies shed some light on it, but the full picture depends on how automation plays out in these trades."

The second version is stronger for reasons that have nothing to do with rare words:

• Cause strength matches reality. Fostered the idea is right for a slow cultural shift; caused by universities is not.
• The root cause is named. Boils down to status does the filtering the reader needs.
• Evidence claims are calibrated. Bears out where the data confirms, shed some light on where it only helps, does not yet show where it is missing.
• No proven. The writer never claims more than the evidence gives.

A Part 3 exchange

Examiner: Why do you think so many people move to cities?

Candidate: Several things, but it boils down to work. Higher wages drive most of it directly. Then there's a slower effect: once a few families move, that fosters networks that make it easier for the next ones to follow.

Examiner: Have government attempts to slow this worked?

Candidate: Their efficacy is limited. Rural subsidies are quite efficient to run, but the data doesn't really bear out any long-term effect on where people choose to live.

Common mistakes

• Using cause or drive for gradual, mixed effects. Reach for foster or contribute to when the effect developed over time from several sources.
• Treating foster as always positive. Foster complacency and foster dependency are correct and useful.
• Prove and proven in essays. Almost always an overclaim. Use bear out if the evidence confirms, suggest if it only points.
• Born out for borne out.
• Shed a light on, shedded light on, shed light to. The form is fixed: shed light on.
• Confusing efficacy with efficiency. One asks did it work; the other asks how cheaply.
• Pan out the plan. Pan out takes no object.

Quick check

1. Which sentence matches the strength of the cause to the effect?

A. "Tax breaks caused a culture of entrepreneurship within a month." B. "Tax breaks fostered a culture of entrepreneurship over the following decade." C. "Tax breaks proved a culture of entrepreneurship."

2. A candidate writes: "The evidence bears out that cities might be more attractive." What is the problem?

A. Bear out needs the object the government. B. Bear out claims confirmation, but might be signals the writer is not sure; the claim and the verb contradict each other. C. Bear out can only be used in the negative.

3. A policy is cheap to run but has not reduced pollution. Which sentence is accurate?

A. "The policy has high efficacy but low efficiency." B. "The policy is efficient but has shown little efficacy." C. "The policy is efficient, so it must be effective."

Answers: 1-B, 2-B, 3-B. In question 1, a culture develops gradually from conditions, which is foster's job; caused is too direct and proved takes the wrong kind of object. In question 2, bears out confirms. The object should be a claim the writer stands behind, such as the link between wages and migration. Hedging inside the object undoes the verb. In question 3, efficient covers cost and efficacy covers results; option C confuses the two.

Practice prompt

Writing Task 2 style: "What are the causes of food waste in wealthy countries, and what can be done about it?"

Write one paragraph of four to five sentences. Include one cause described with foster or contribute to, not cause. Add one evidence claim using bear out or suggest at the honest strength. Finish with one judgment of a solution using efficacy. Do not use prove.

If you want to practice choosing between bear out, suggest, and prove in real sentences, not just recognizing the difference, try Lyra Practice.

Sources

• IELTS Writing Band Descriptors (Task 1 & Task 2) — IELTS
• IELTS Speaking Band Descriptors — IELTS

Related

• Why Memorizing Band 9 Vocabulary Isn't Enough for IELTS
• IELTS Vocabulary for Opinions and Arguments
• Foster vs Encourage: What's the Difference?
• Bear Out vs Confirm: What's the Difference?
• Shed Light On vs Explain vs Reveal: What's the Difference?
• Efficacy vs Efficiency: What's the Difference?
• IELTS Vocabulary Practice