Sufficient Evidence: Study Guide (English Language 2.5)

How much evidence is enough?

Suppose a friend says, “Our school canteen is awful,” and offers one example: yesterday’s pasta was cold. You would probably not be convinced. One cold plate is a fact, but it does not justify the word “awful”. Suppose instead your friend produces a month of complaints, a survey of 200 pupils and a hygiene report. Now the claim has real support.

The course framework puts it like this: an effective argument contains sufficient evidence; evidence is sufficient when its quantity and quality provide apt support for the argument. The word apt means fitting. Evidence is sufficient not when there is a lot of it but when there is enough of the right kind to justify this particular claim.

Two measures: quantity and quality

Measure	Question	Weak	Strong
Quantity	Is there enough of it for this claim?	One example for a sweeping claim.	Several independent examples or a large, well-chosen sample.
Quality	Is each piece relevant, accurate, credible and representative?	A rumour, an outdated figure, a single unrepresentative case.	A verifiable fact, a recent study, a qualified source.

Both matter. Ten weak pieces do not equal one strong one, and one strong piece may not be enough for a broad claim. The two measures also interact: better quality can compensate for lower quantity (a rigorous study of 5,000 people beats ten anecdotes), but only up to a point, because no single source can support a very broad claim by itself.

The scope of the claim sets the standard

The bigger or stronger the claim, the more evidence it needs. Look at the words in the claim:

Claim wording	What it demands
“Some pupils find the timetable stressful.”	A modest amount of evidence: a few clear cases.
“Most pupils find the timetable stressful.”	A representative sample or survey showing a majority.
“All pupils find the timetable stressful.”	Almost impossible: a single contrary case would break it.
“The timetable causes stress.”	Evidence of cause, not only that stress and timetable occur together.
“The timetable is the worst in the country.”	A comparison with others, not just local complaints.

A reliable way to improve an argument is to narrow the claim to what the evidence can support. “Most pupils in Years 10 and 11 report that the timetable leaves too little time to eat” is easier to defend than “The timetable is unbearable.”

Common ways evidence falls short

1. Too little. A single example offered for a general claim. This is sometimes called a hasty generalisation.
2. Unrepresentative. The cases chosen are unusual, or the sample was self-selected. A survey answered only by people who feel strongly may not reflect everyone.
3. Irrelevant. The evidence is true but does not bear on the claim, for example arguing about safety using a statistic about cost.
4. Out of date. A ten-year-old figure used to describe a fast-changing situation.
5. Unreliable source. An unnamed, biased or unqualified source.
6. Only one type. A claim supported only by anecdote, or only by statistics, may leave gaps a sceptic will notice.
7. Evidence without explanation. A good fact left unexplained may not show why it supports the claim (Topic 3.1).

Too much can also be a problem

Sufficiency does not mean piling up. A paragraph that lists nine near-identical examples can bore the audience and bury the strongest one. A writer should choose enough evidence, then spend words on commentary. If three examples show the point, adding six more adds little. The goal is apt support, not exhaustive support.

Sufficiency depends on the audience too

An audience already inclined to agree needs less; a sceptical or hostile audience needs more, and more varied, evidence. A specialist audience expects rigorous sources; a general audience may be satisfied by a clear example and a trusted statistic. Writers who sense resistance often add several types of evidence (a statistic, an example, an authority) so that readers with different standards each find something persuasive.

A public-domain example: “Let Facts be submitted”

The Declaration of Independence (1776) makes a very large claim: that the King of Great Britain has pursued “a long train of abuses and usurpations” showing a design to impose “absolute Despotism” on the colonies. The authors know that such a claim requires heavy support, and they say so: “To prove this, let Facts be submitted to a candid world.”

What follows is a list of grievances, each beginning “He has…”. The list works as evidence by quantity: dozens of specific complaints, each concrete and checkable by the colonists who experienced them. The claim is broad (a design of despotism), so a single complaint would have been insufficient. The accumulation shows a pattern, which is what the claim asserts. The writers also frame the list as facts for a “candid”, that is, fair-minded, world, which signals their awareness of the audience’s need to be convinced.

Worked example 1: diagnosing insufficient evidence

Task. Evaluate the sufficiency of this paragraph, written by Marlbridge with invented details, and suggest two improvements.

Mobile phones should be banned in all schools. My cousin’s school banned them and her grades improved. Phones are distracting. A teacher told me she had to confiscate a phone last week.

Step 1: Identify the claim. “Mobile phones should be banned in all schools.” This is a broad claim of policy: all schools.

Step 2: Judge quantity and quality.

• Quantity: two examples (a cousin and one confiscation).
• Quality: both are anecdotes, secondhand, unmeasured and unrepresentative. “Grades improved” may have had other causes. A single confiscation shows phones are used, not that they harm learning.

Step 3: Compare to the scope. The claim says all schools, but the evidence concerns one school and one incident. The gap is wide.

Step 4: Improve.

1. Narrow the claim to what can be defended: “Schools should ban mobile phones during lessons, because phones reduce attention.”
2. Add stronger evidence: a study measuring attention or results in schools with and without bans, a survey of teachers on interruptions, and, to meet objections, a note that phones may be used at break or in emergencies.

Result.

Schools should ban mobile phones during lessons. In a study of 12 schools, pupils in the six that introduced a lesson-time ban gained on average four marks more on a standard test than pupils in the six that did not (invented figures). In a survey of 90 teachers, 71 said phones were the most frequent cause of interruption. A ban would not need to apply at break time or in emergencies, so pupils could still contact their families.

Check. The new version has a narrower, defensible claim, two types of evidence (study, survey), representative numbers and a concession. It is sufficient for the claim it now makes.

Worked example 2: why the Declaration needs so many facts

Task. Explain why the Declaration of Independence uses a long list of grievances to support its central claim, and what the sentence “To prove this, let Facts be submitted to a candid world” contributes.

Step 1: Identify the claim. The King’s repeated acts show “a design to reduce them under absolute Despotism”. The claim is about intent and pattern, which is strong and hard to prove.

Step 2: Link scope to quantity. A pattern cannot be shown by one event. Only a series of related acts, each pointing in the same direction, can establish a pattern. The long list supplies the quantity the claim demands.

Step 3: Link to quality. The grievances are specific (dissolving legislatures, obstructing justice, quartering troops) so each could be checked by those who lived through them. Specific, checkable items give quality as well as quantity.

Step 4: Explain the framing sentence. “To prove this, let Facts be submitted to a candid world” announces that the writers know the claim needs proof, and that they appeal to a fair-minded audience. It builds credibility by presenting what follows as facts and not as rhetoric, and it points to the audience (the world), not only to the King.

Check. The answer connects the scope of the claim to the amount of evidence, comments on quality, and explains the sentence’s effect. Writing only “they list many reasons” would not explain why.

How the exam asks about sufficiency

• Reading: whether the evidence in a passage adequately supports the claim; what additional kind of evidence would strengthen it.
• Writing: which sentence added to a paragraph would best provide sufficient support; which revision narrows a claim to match the evidence.
• Essays: in the argument essay, sustain a claim with enough relevant evidence; in the synthesis essay, draw on enough sources to support your position without letting them replace your own thinking.

Common misconceptions

• “More evidence is always better.” Quality, relevance and variety matter. Too many similar examples can bury the best one.
• “One strong example is enough for any claim.” It may be enough for a narrow claim, but never for a sweeping one.
• “A statistic from an authority settles the matter.” Check that it is relevant, current and representative.
• “If I cannot find enough evidence, I should exaggerate.” The better move is to narrow the claim.
• “Sufficiency is only about numbers.” It also concerns the kind of evidence and whether it fits the claim.
• “Evidence is sufficient if I believe it.” Sufficiency is judged by what a reasonable audience would accept.

Where this leads

Topic 2.6, Identifying the thesis of an argument, moves to the overarching claim that all this evidence ultimately supports. Practise with the practice questions and the checklist.