Claim, Evidence, Reasoning
Also known as CER
A three-part structure for an argument paragraph or answer: state a claim, give evidence that supports it, then explain how the evidence proves the claim.
- Claim only
- The plant grew because of the sun.
- CER
- Light made it grow: it gained 6 cm in a week to the dark plant's 1 cm, and plants use light to make food.
In practice
Claim, evidence, reasoning, or CER, is a simple structure for an argument: make a claim that answers a question, give evidence that supports it, and explain the reasoning that connects the evidence to the claim. It began in science classrooms, where it helps students write explanations of what an experiment showed, and is now used for writing in every subject.
The claim is a one-sentence answer to the question. The evidence is specific data, observations or quotations, not general knowledge. The reasoning explains why that evidence supports the claim, often by naming a rule, principle or scientific idea. Most weak CER answers fail at the third step: they list evidence and assume the connection is obvious.
CER is close kin to other paragraph frameworks. A body paragraph in an essay often follows the same order as a topic sentence, evidence and analysis, and the Toulmin model of argument calls the reasoning step the warrant. Some teachers add a rebuttal step, making CERR, to bring in the counterargument.
Teachers like CER because it makes thinking visible. A student who writes only a claim may have guessed; a student who adds evidence shows what they noticed; a student who explains the reasoning shows they understand why it matters. The same habit helps any writer. A lab report, a book review, a business case and a court brief all ask a reader to accept a conclusion, and each one works better when the link between the facts and the conclusion is written down instead of assumed. Getting into the habit early also makes longer essays easier, because each body paragraph becomes a small CER of its own.
CER in a scene
INT. POLICE STATION - INTERVIEW ROOM - NIGHT
A muddy boot in an evidence bag on the table. DETECTIVE OKAFOR (40s) sets a soil report beside it. Her partner LUIS (30s) reads over her shoulder.
OKAFOR
He was at the quarry. That's the claim.
She taps the report.
OKAFOR
The clay on this boot has limestone dust, and the only limestone within fifty miles is at the quarry. So that's where he walked.
Opens as a new Plot project once you sign in or create a free account. Inkwell keeps this copy for 24 hours.
Okafor says the claim, points to the evidence and then supplies the reasoning, the fact that makes the evidence mean something. Without her last line, the mud is just mud. That last step is the one CER exists to teach.
Claim, evidence, reasoning examples
Science: Question: what does salt do to the freezing point of water? Claim: salt lowers it. Evidence: plain water froze at 0°C; salt water was still liquid at -5°C. Reasoning: dissolved salt gets in the way of water molecules forming ice, so the water must get colder before it freezes.
English: Question: is Lady Macbeth more ambitious than her husband at the start of the play? Claim: yes. Evidence: she calls on spirits to "unsex me here" and calls Macbeth "too full o' th' milk of human kindness." Reasoning: she asks to lose the feelings that might stop her, while she sees Macbeth's kindness as the weakness that could stop him.
History: Question: why did the Dust Bowl drive families west? Claim: farms failed when the topsoil blew away. Evidence: dust storms in the 1930s stripped millions of acres. Reasoning: without topsoil, crops could not grow, so farm families lost both food and income.
How to write a CER
Claim: answer the question in one complete sentence. Do not start with "I think"; state it directly, and make it something the evidence can actually test, not a vague feeling.
Evidence: give two or three pieces of specific support: numbers, observations, quotations or examples. Name where each comes from.
Reasoning: explain why the evidence proves the claim. Use "because" or "this shows" and bring in the principle, rule or idea that links them. This is usually the longest part.
Reread it as a skeptic. If someone could accept your evidence and still reject your claim, the reasoning is missing a step. Add it.
What makes good reasoning
Good reasoning names the bridge between evidence and claim. In science, the bridge is often a principle ("plants use light to make food"); in English, it is an interpretation of the quoted words; in history, it is a cause and its effect.
Reasoning should also explain why the evidence is enough. One data point is weaker than a pattern; a quotation is stronger when you explain the specific word that matters. Restating the evidence in different words is not reasoning.
Using a CER graphic organizer
Many teachers hand out CER as a three-column or three-row chart: the question at the top, then boxes for the claim, the evidence and the reasoning. Filling in the boxes before writing the paragraph separates thinking from wording, which is useful when the science or the text is hard.
Use the chart as a check, not a script. Once each box is filled, turn it into sentences that flow: the claim as a topic sentence, the evidence with its source, and the reasoning joined by "because" or "this shows that". A paragraph that reads like three boxes stitched together usually needs transitions.
For longer answers, repeat the evidence and reasoning boxes. Two pieces of evidence, each with its own explanation, make a stronger case than three pieces of evidence followed by one sentence of reasoning that tries to cover them all.
Common questions
What is claim, evidence, reasoning?
A three-part structure for an argument: a claim that answers a question, evidence that supports it and reasoning that explains how the evidence proves the claim.
What does CER stand for?
Claim, evidence, reasoning. Some teachers add a second R for rebuttal, making CERR.
What is an example of claim, evidence, reasoning?
Claim: salt lowers water's freezing point. Evidence: salt water stayed liquid at -5°C. Reasoning: salt interferes with ice forming, so the water must get colder to freeze.
What is the difference between evidence and reasoning?
Evidence is the data, quotation or observation. Reasoning is the explanation of why that evidence supports the claim.
Is CER only for science?
No. It started in science classrooms, but teachers use it for literary analysis, history and any short argument answer.
How long should a CER be?
Usually one paragraph: a one-sentence claim, two or three pieces of evidence and several sentences of reasoning.
How do you write good reasoning in a CER?
Explain why the evidence supports the claim, using a principle, rule or interpretation that links them. Start with "this shows that" or "because", and avoid simply repeating the evidence in new words.