Claims and Evidence
A persuasive speech stands or falls on the relationship between its claim and its evidence. A claim without evidence is an assertion; evidence without a claim is a pile of facts. This page shows how to build the bridge between them.
What makes a claim persuasive
| Quality | Question | Example |
|---|---|---|
| Clear | Can the audience state it back? | “The school should ban single-use plastic bottles at the canteen.” |
| Contestable | Could a reasonable person disagree? | Not “Water is important”, but “The school should provide free water stations.” |
| Specific | Does it name the action and the scope? | “At the canteen” rather than “everywhere”. |
| Relevant | Does it matter to this audience? | Connected to a current decision or shared concern. |
| Defensible | Can it be supported with available evidence? | The speaker can name sources and answer objections. |
Types of evidence
| Type | Strength | Limitation | Best used for |
|---|---|---|---|
| Statistics | Shows scale and pattern. | Can be misread or decontextualised. | Establishing the size of a problem. |
| Research findings | Systematic and peer-reviewed. | May not generalise to this setting. | Showing what is likely to work. |
| Expert opinion | Brings specialised knowledge. | Experts disagree; credentials vary. | Interpreting complex evidence. |
| Case example | Concrete and memorable. | One case may not be typical. | Illustrating a mechanism or impact. |
| Personal experience | Vivid and credible for the speaker. | Not representative; privacy issues. | Grounding a claim in lived experience. |
| Analogy | Makes an unfamiliar idea clear. | Does not prove anything. | Explaining, not establishing. |
| Precedent | Shows that something has been done before. | Context may differ. | Arguing that a proposal is feasible. |
Use more than one type where possible. A statistic establishes scale, a case example shows what it looks like, and an expert interpretation explains why it matters.
The warrant
The warrant is the reasoning that connects evidence to claim. It is often left unsaid, which is where arguments become weak. Say it aloud: “This evidence supports my claim because ...”
| Claim | Evidence | Warrant |
|---|---|---|
| The canteen should stop selling bottled water. | Students throw away 400 bottles a week. | Most of those bottles are not recycled, so the waste ends up in landfill. |
| The school should start later. | Teenage sleep cycles shift later during adolescence. | A later start aligns the school day with when students can actually sleep. |
| The council should plant more trees. | Trees reduce surface temperature in summer. | Lower surface temperature makes public spaces safer and more usable during heatwaves. |
If the warrant is contested, support it too. “Most bottles are not recycled” is itself a claim that needs evidence.
Sufficiency
How much evidence is enough? It depends on the claim and the audience. A small change to a school routine may need one or two strong reasons. A claim about a whole population needs representative data. A claim about what caused an event needs a plausible mechanism and evidence against alternatives.
| Claim scale | Evidence needed |
|---|---|
| “This bench is damaged.” | Direct observation or a photograph. |
| “The canteen wastes food.” | Records or a small audit over time. |
| “Most students want a later start.” | A representative survey, not a show of hands in one class. |
| “Later starts improve learning.” | Research across multiple schools, with attention to context. |
Testing evidence
- Is it relevant to the claim?
- Is the source credible and current?
- Is it representative of the group being discussed?
- Is the comparison fair?
- Does it measure what it claims to measure?
- Is there a counterexample that needs addressing?
- Could the audience check it if they wanted to?
Evidence in speech
Listeners cannot inspect a table. Present evidence in small, digestible pieces and explain what it means. One well-explained statistic is stronger than five numbers read aloud.
| Written style | Spoken style |
|---|---|
| “Data from the 2024 audit indicates a 32 per cent reduction.” | “The 2024 audit found about a third less waste than the year before.” |
| “The correlation was statistically significant.” | “The pattern was strong enough that it was unlikely to be chance.” |
| “A majority of respondents ...” | “Most of the people surveyed ...” |
Activity: claim-evidence-warrant
- Write a claim you actually believe about school or community life.
- Find two pieces of evidence that support it.
- Write the warrant for each piece of evidence.
- Find one counterexample or limitation.
- Explain the claim aloud in sixty seconds using both pieces of evidence.
- Ask a listener what they would need to be convinced.
Evidence does not speak for itself. The audience needs to hear why it matters. If you cannot explain the link, the evidence is not yet doing any work.
Common errors
- Claim stacking. Three claims in one sentence cannot each be supported.
- Evidence dump. A list of facts without a through-line.
- Missing warrant. The audience cannot see why the evidence supports the claim.
- Unrepresentative examples. One case treated as the norm.
- Appealing to a vague authority. “Experts say” without naming them.
- Ignoring counterevidence. It weakens credibility when the audience knows it exists.
Next, study persuasive structure to arrange claims and evidence for a listener. The rhetorical devices page adds emphasis and memory.